
<PAGE>

                                                                 EXHIBIT 10.1a



     Amendment No. 1 to MARK CENTERS LIMITED PARTNERSHIP AGREEMENT,  dated as of
the 3rd day of June 6, 1996  ("Agreement")  by and among Mark Centers  Trust and
Marvin L. Slomowitz.

     WHEREAS,  pursuant  to Section  3.2C of the  Agreement  and a  Subscription
Agreement,  dated July 14, 1995,  L&J Realty  Company has subscribed for 2000 OP
Units;

     WHEREAS,  pursuant to Section  12C of the  Agreement  the  General  Partner
desires to amend the Agreement to admit L&J Realty Company as a Limited Partner.

     NOW,  THEREFORE,  the Agreement is amended as follows:  

     1. Any capitalized terms herein which are not otherwise defined herein
shall have the same meaning as set forth in the Agreement.

     2. L & J Realty Company is hereby admitted as a Limited Partner of the
Partnership.

     3.  Effective  as of  July  14,  1995  the  total  number  of all  OP units
outstanding is 9,553,000 and each Partner is deemed to hold OP Units as follows:

                                OP UNITS                 PERCENTAGE  INTEREST
                                --------                 --------------------
     Company                    7,751,000                       81.14% 
     Limited Partner 
     Marvin L. Slomowitz        1,800,000                       18.84%
     Limited Partner 
     L & J Realty Company           2,000                         .02%

     4. Schedule A to the Partnership Agreement shall be deleted in its entirety
and shall be  replaced  with a new  Schedule A which is annexed  hereto. 

     5. The effective date of this Amendment No. 1 shall be July 14, 1995.

     6. Except as amended by this Amendment No. 1, the Agreement shall remain in
full force and  effect. 

     IN WITNESS WHEREOF, the Company has executed this Amendment No. 1 as of the
14th day of July, 1995.

GENERAL PARTNER:
MARK CENTERS TRUST, a Maryland Real Estate Investment Trust

By: /s/ David S. Zook
    ------------------------------
Name:   David S. Zook
Title:  Executive Vice President


                                   SCHEDULE A
                               PERCENTAGE INTEREST

              General Partner                           81.14%

              Marvin L. Slomowitz                       18.84%

              L&J Realty                                  .02%
<PAGE>

                                                                       EXHIBIT J


                SECOND AMENDMENT TO LIMITED PARTNERSHIP AGREEMENT

                  THIS SECOND AMENDMENT, dated as of August 12, 1998, to
that Limited Partnership Agreement, dated as of June 3, 1994, and as amended by
the First Amendment to the Partnership Agreement dated as of June 6, 1996 (the
"Partnership Agreement"), of MARK CENTERS LIMITED PARTNERSHIP, a Delaware
limited partnership (the "Partnership"). Capitalized terms used herein but not
defined herein shall have the meanings given such terms in the Partnership
Agreement.

                                   BACKGROUND

                  The Partnership is a party to a certain Contribution and Share
Purchase Agreement dated as of April 15, 1998 (the "Contribution Agreement")
pursuant to which, among other things, the Partnership has agreed to acquire
partnership interests in certain unaffiliated partnerships and real and personal
property owned by such partnerships and affiliates of such partnerships in
consideration for, among other things, Partnership Interests in the Partnership.
Pursuant to Section 3.2(B) of the Partnership Agreement, the General Partner of
the Partnership has the power and authority to issue additional Partnership
Interests to Persons in exchange for additional Capital Contributions. The
General Partner, pursuant to the exercise of such authority and in accordance
with Section 12(C) of the Partnership Agreement, has determined to execute this
Second Amendment to the Partnership Agreement to evidence: (i) the issuance of
additional Partnership Interests and the admission of the other signatories
hereto as Limited Partners of the Partnership and (ii) certain other amendments
to the Partnership Agreement.

                  NOW,  THEREFORE,  the parties hereto,  for good and sufficient
consideration  and intending to be legally bound,  hereby amend the  Partnership
Agreement as follows:

                  1. The Partnership Agreement is hereby amended to reflect the
admission as Limited Partners on the date hereof of those Persons whose names
are set forth on Annex "A" attached hereto and made a part hereof and whose
authorized signatures appear on the signature page hereto, each of whom shall
have such number of Partnership Interests as shall be set forth opposite such
signatory's name on Annex "A".

                  2. The Partnership Interests issued hereby shall have the same
rights, preferences, privileges and designations as the Limited Partner
Partnership Interests which have heretofore been issued by the Partnership,
including, but not limited to, the right to convert such Partnership Interests
into Common Shares of Beneficial Interest, par value, $.01 per share, of the
General Partner pursuant to Section 3.2(C) of the Partnership Agreement, as
amended hereby.


<PAGE>




                                                                               
                  3. The second  sentence of Section  3.2(B) of the  Partnership
Agreement  is hereby  amended by adding the  following  underscored  language as
follows:

                           "The  number of OP Units  issued to the  Contributing
                           Party under clause (i) of this  Section  3.2(B) shall
                           be equal to either (a) such amount as may be fixed by
                           agreement between the General Partner, in the General
                           Partner's sole discretion, and the Contributing Party
                           or (b) the  quotient  (rounded to the  nearest  whole
                           number arrived at by dividing..."

                  4. Section 3.2(C) of the Partnership Agreement is hereby
amended by adding to the end thereof the following sentence:

                           "If the Company is unable to issue Common Shares in
                           accordance with this Section 3.2(C) it shall redeem
                           the requested OP Units for cash for an amount equal
                           to the Market Price (as defined in Section 3.2(B))
                           calculated as if one OP Unit equaled one Common Share
                           (subject to the anti-dilution protections set forth
                           in this Section 3.2(C)."

                  5.       Section 5 of the Partnership Agreement is hereby 
amended by adding the following new paragraphs (D) through (G) at the end 
thereof:

                           "D. The General Partner may not, without the consent
                           of all of the Limited Partners affected thereby,
                           change its policy of holding its assets and
                           conducting its business solely through the
                           Partnership, nor may any transactions described in
                           Section 5(E) or 5(F), without the consent of all the
                           Limited Partners affected thereby, be structured in a
                           manner which will change the General Partner's policy
                           of holding its assets and conducting its business
                           through the Partnership (or the Surviving Partnership
                           (defined below), if applicable)), if the result of
                           such transaction is the recognition of gain for
                           federal income tax purposes by such Limited Partners.


                                       2

<PAGE>



                           E. Whether or not Section 5(D) hereof is applicable,
                           the General Partner shall not, unless Section 5(F) is
                           applicable, engage in any merger, consolidation or
                           other combination with or into another person, sale
                           of all or substantially all of its assets or any
                           reclassification, recapitalization or similar
                           transaction (each a "Termination Transaction"),
                           unless such Termination Transaction is one in
                           connection with which each Limited Partner either
                           will receive, or will have the right to elect to
                           receive, for each OP Unit held by such Limited
                           Partner, an amount of cash, securities, or other
                           property equal to the product of the number of Common
                           Shares into which such OP Unit is convertible and the
                           greatest amount of cash, securities or other property
                           paid to a holder of one Common Share in consideration
                           of one Common Share pursuant to the terms of the
                           Termination Transaction; provided that; if, in
                           connection with the Termination Transaction, a
                           purchase, tender or exchange offer shall have been
                           made to and accepted by the holders of the
                           outstanding Common Shares, each holder of OP Units
                           shall receive, or shall have the right to elect to
                           receive, the greatest amount of cash, securities, or
                           other property which such holder would have received
                           had it exercised its exchange right (as set forth in
                           Section 3.2(C)) and received Common Shares in
                           exchange for its OP Units immediately prior to the
                           expiration of such purchase, tender or exchange offer
                           and had thereupon accepted such purchase, tender or
                           exchange offer and then such Termination Transaction
                           shall have been consummated.

                                      
                                        3



<PAGE>



                           F. Whether or not Section 5(D) hereof is applicable,
                           the General Partner may merge, or otherwise combine
                           its assets, with another entity without satisfying
                           the requirements of Section 5(E) hereof if: (i)
                           immediately after such merger or other combination,
                           substantially all of the assets directly or
                           indirectly owned by the surviving entity, other than
                           OP Units held by such General Partner, are owned
                           directly or indirectly by the Partnership or another
                           limited partnership or limited liability company
                           which is the survivor of a merger, consolidation or
                           combination of assets with the Partnership (in each
                           case, the "Surviving Partnership"); (ii) the Limited
                           Partners own a percentage interest of the Surviving
                           Partnership based on the relative fair market value
                           of the net assets of the Partnership (as determined
                           pursuant to Section 5(G)) and the relative fair
                           market value of the other net assets of the Surviving
                           Partnership (as determined pursuant to Section 5(G))
                           immediately prior to the consummation of such
                           transaction; (iii) the rights, preferences and
                           privileges of the Limited Partners in the Surviving
                           Partnership are at least as favorable as those in
                           effect immediately prior to the consummation of such
                           transaction and as those applicable to any other
                           limited partners or non-managing members of the
                           Surviving Partnership; and (iv) such rights of the
                           Limited Partners include the right to exchange their
                           interests in the Surviving Partnership for at least
                           one of: (A) the consideration available to such
                           Limited Partners pursuant to Section 5(E), or (B) if
                           the ultimate controlling person of the Surviving
                           Partnership has publicly traded common equal
                           securities, such common equity securities, with an
                           exchange ratio based on the relative fair market
                           value of such securities (as determined pursuant to
                           Section 5(G)) and the Common Shares.

                           G. In connection with any transaction permitted by
                           Section 5(E) or 5(F), the relative fair market values
                           shall be reasonably determined by the General Partner
                           in good faith as of the time of such transaction and,
                           to the extent applicable, shall be no less favorable
                           to the Limited Partners than the relative values
                           reflected in the terms of such transactions."

                  6.       Section 7.6(A) of the Partnership Agreement is hereby
 amended to change the reference to "Prop. Reg. ? 1.704-3(b)(1)" to "Regulations
 Section


                  7.       The first sentence of Section 12(B)(i) of the 
Partnership Agreement is hereby amended and restated as follows:


                                       4



<PAGE>



                           "(i) No Limited Partner or substituted Limited
                           Partner shall, without the prior written consent of
                           the General Partner (which consent may be given or
                           withheld in the sole discretion of the General
                           Partner), sell, assign, distribute or otherwise
                           transfer (a "Transfer") all or any part of his
                           interest in the Partnership except by operation of
                           law, gift (outright or in trust) or by sale, in each
                           case to or for the benefit of a Permitted Transferee
                           (as defined below), except for (a) pledges or other
                           collateral transfers effected by a Limited Partner to
                           secure the repayment of a loan and (b) the exchange
                           of OP Units for shares of Common Stock of the
                           Company, pursuant to Section 3.2(C) above. For
                           purposes of this Section 12(B)(i), the term
                           "Permitted Transferee" means (i) any partner or other
                           equity owner of a Limited Partner; (ii) an equity
                           owner of any partner or other equity owner of a
                           Limited Partner; (iii) members of the Immediate
                           Family (as defined below) of any equity owner of a
                           Limited Partner (or any equity owner thereof) and
                           trusts for the benefit of one or more members of the
                           Immediate Family of the Limited Partner (or any
                           equity owner thereof) created for a state and/or gift
                           tax purposes and/or (iv) any public charity, public
                           foundation or charitable institution as defined in
                           Section 501(C)(3) of the Code. For purposes of this
                           Section 12(B)(i), the term "Immediate Family" means,
                           with respect to any natural person, such natural
                           person's spouse, parents, parents-in-law,
                           descendants, nephews, nieces, brothers, sisters,
                           brothers-in-law, sisters-in-law and children-in-law."

                  8. Section 16(A)(ii) of the Partnership Agreement is hereby
amended and restated as follows:

                           "(ii) except (x) as otherwise provided for in this
                           Agreement, (y) as required by law or (z) in the case
                           of technical modifications which do not have a
                           material adverse impact on any Partner, to modify the
                           allocation of Profits and Losses or distributions
                           among the Partners as provided for in Sections 7 and
                           8 above, respectively; or"


                                       5

<PAGE>



                  9.  Section 16(A)(iii) of the Partnership Agreement is 
hereby amended to include reference to Sections 5(D) through (G).

                  10. By execution of this Second Amendment to the Partnership
Agreement, each of the signatories hereto agrees to be bound by each and every
term of the Partnership Agreement as amended hereby from and after the date
hereof.

                  11. Except as expressly set forth in this Second Amendment,
the Partnership Agreement is hereby ratified and confirmed in each and every
respect.

                  IN WITNESS WHEREOF, this Second Amendment to the Limited
Partnership Agreement is executed and delivered as of the date first written
above.

                                                    MARK CENTERS TRUST,
                                                     General Partner


                                                    By: /s/ Joshua Kane
                                                        -----------------------
                                                            Joshua Kane

                                                    Title: Senior Vice President
                                                           ---------------------

                                                    Limited Partners:

                                                    __________________________

                                                    __________________________

                                                    __________________________

                                                    __________________________


                                       
                                       6
<PAGE>

                THIRD AMENDMENT TO LIMITED PARTNERSHIP AGREEMENT


                  THIS THIRD AMENDMENT, dated as of December 17, 1998, to that
Limited Partnership Agreement, dated as of June 3, 1994, and as amended by the
First Amendment to the Partnership Agreement dated as of June 6, 1996 and as
amended by the Second Amendment to the Partnership Agreement dated as of August
12, 1998 (the "Partnership Agreement"), of ACADIA REALTY LIMITED PARTNERSHIP, a
Delaware limited partnership (the "Partnership"). Capitalized terms used herein
but not defined herein shall have the meanings given such terms in the
Partnership Agreement.

                                   BACKGROUND

                  The General Partner, pursuant to the exercise of such
authority and in accordance with Section 12(C) of the Partnership Agreement, has
determined to execute this Third Amendment to the Partnership Agreement to
evidence the assignment of certain Partnership Interests and the admission of
the other signatories hereto as Limited Partners of the Partnership.

                  NOW, THEREFORE, the parties hereto, for good and sufficient
consideration and intending to be legally bound, hereby amend the Partnership
Agreement as follows:

                  1. The Partnership Agreement is hereby amended to reflect (i)
the withdrawal of RD G.O. Properties, L.P. as a limited partner and (ii) the
admission as Limited Partners of those Persons whose names are set forth on
Annex "A" attached hereto and made a part hereof and whose authorized signatures
appear on the signature page hereto, each of whom shall have such number of
Partnership Interests as shall be set forth opposite such signatory's name on
Annex "A".

                  2. The Partnership Interests issued hereby shall have the same
rights, preferences, privileges and designations as the Limited Partner
Partnership Interests which have heretofore been issued by the Partnership,
including, but not limited to, the right to convert such Partnership Interests
into Common Shares of Beneficial Interest, par value, $.01 per share, of the
General Partner pursuant to Section 3.2(C) of the Partnership Agreement, as
amended hereby.

                  3. By execution of this Third Amendment to the Partnership
Agreement, each of the signatories hereto agrees to be bound by each and every
term of the Partnership Agreement as amended hereby from and after the date
hereof.

                  4. Except as expressly set forth in this Third Amendment, the
Partnership Agreement is hereby ratified and confirmed in each and every
respect.

                  5. This Third Amendment may be executed in any number of
counterparts, each of which shall be deemed to be an original as against any
party whose signature appears thereon, and all of which shall together
constitute one and the same instrument. This Third Amendment shall become
binding when one or more counterparts hereof, individually taken together, shall
bear the signatures of all of the parties reflected hereon as the signatories.


                                       
<PAGE>



                  IN WITNESS WHEREOF, this Third Amendment to the Limited
Partnership Agreement is executed and delivered as of the date first written
above.

                                           ACADIA REALTY TRUST,
                                            General Partner


                                           By: /s/ Kenneth F. Bernstein
                                              ---------------------------------
                                                   Kenneth F. Bernstein

                                          Title: President
                                                 ------------------------------

Substituted Limited Partners:

EVAN FRAZIER REALTY LLC


By: /s/ Kenneth F. Bernstein
   ---------------------------------
   Name:  Kenneth F. Bernstein
   Title: Member

RD GREENBELT, INC.


By: /s/ Kenneth F. Bernstein
   ---------------------------------
   Name:  Kenneth F. Bernstein
   Title: President

KAL PARTNERS L.P.


By: /s/ Gregory Manocherian
   ---------------------------------
   Name:  Gregory Manocherian
   Title: General Partner



/s/ Michael A. Young
------------------------------------
MICHAEL A. YOUNG



/s/ Mindy White
------------------------------------
MINDY WHITE


                                       2
<PAGE>



S & J ROTH REVOCABLE TRUST


By: /s/ Stephen Roth
   ------------------------------------
   Name:  Stephen Roth
   Title: Trustee

RABINOWITZ FAMILY 1991 TRUST


By: /s/ Martin J. Rabinowitz
   ------------------------------------
   Name:  Martin J. Rabinowitz
   Title:    Trustee

RABINOWITZ FAMILY 1986 TRUST


By: /s/ Steven M. Rabinowitz
   ------------------------------------
   Name:  Steven M. Rabinowitz, Esq.
   Title: Trustee

Withdrawing Limited Partner:

RD G.O. PROPERTIES, L.P.

By: RD Greenbelt, Inc., its general
    partner


    By: /s/ Kenneth F. Bernstein
        ------------------------------
       Name:  Kenneth F. Bernstein
       Title: President


                                       3
<PAGE>



                                    ANNEX "A"


Name of Limited Partner                 Number of Partnership Interests
-----------------------                 -------------------------------
Evan Frazier Realty LLC                              294,434
20 Soundview Marketplace
Port Washington, NY  11050
Taxpayer ID#: 11-3363230

RD Greenbelt, Inc.                                    55,011
20 Soundview Marketplace
Port Washington, NY 11050

KAL Partners L.P.                                    102,068
3 New York Plaza
18th Floor
New York, NY  10004
Taxpayer ID: 13-3928884

Michael A. Young                                      34,005
304 East 65th Street
Apt. 36B
New York, NY  10021
Soc. Sec. #: ###-##-####

Mindy White                                           17,029
44 Garden Road
Scarsdale, NY  10583
Soc. Sec. #: ###-##-####

S & J Roth Revocable Trust                            25,517
c/o Stephen Roth, Trustee
301 Weyyakin Drive
P.O. Box 6120
Ketchum, ID  83340
Taxpayer ID #: ###-##-####


                                       4

<PAGE>

Name of Limited Partner                 Number of Partnership Interests
-----------------------                 -------------------------------
Rabinowitz Family 1991 Trust                          21,247
c/o Martin J. Rabinowitz, Trustee
1500 Broadway
Suite 1020
New York, NY 10036
Taxpayer ID#: ###-##-####

Rabinowitz Family 1986 Trust                          21,247
c/o Martin J. Rabinowitz, 
1500 Broadway
Suite 1020
New York, NY 10036
Taxpayer ID#: 13-6950556



                                       5

