<PAGE>
 
                                                                   EXHIBIT 4.3.2
 
                                FIRST AMENDMENT
                                      TO
                               CREDIT AGREEMENT


This FIRST AMENDMENT (the "FIRST AMENDMENT") by and among XTRA, INC., a Maine
corporation (the "COMPANY"), BANK OF AMERICA ILLINOIS, an Illinois banking
corporation ("BAI") and each of the other Banks and the Agents (each as defined
in the Credit Agreement described below), is entered into as of the 28th day of
June, 1996.

                               R E C I T A L S

     A.   The Company, BAI and each of the other Banks and the Agents have
previously entered into that certain Credit Agreement dated as of June 30, 1995
(the "CREDIT AGREEMENT").

     B.   Each of the Company, the Ultimate Parent and the Parent has requested
that the Banks and the Agents amend certain provisions of the Credit Agreement.

     C.   The Term Loan has been repaid in full and the Company is not entitled
to request any further Loans with respect to the Term Loan.

     D.   The Bank and the Agents are willing to amend the Credit Agreement
subject to the terms and conditions set forth herein.

     NOW, THEREFORE, in consideration of the terms and conditions set forth
herein, any extension of credit or other financial accommodation heretofore, now
or hereafter made by any of the Banks or of the Agents to the Company and for
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto agree as follows:

     1.   RECITALS. The foregoing recitals are accurate and are incorporated
herein and made a part hereof.

     2.   DEFINITIONS. Each initially capitalized term used herein without
definition shall have the meaning set forth for such term in the Credit
Agreement.

     3.   AMENDMENTS.

     A.   The definition of "Indebtedness" set forth in Section 1.1 of the
Credit Agreement is hereby amended by deleting such definition in its entirety
and substituting in lieu thereof the following:
<PAGE>
 
          ""INDEBTEDNESS" means, with respect to any Person, (A) the principal
          amount of all indebtedness of such Person (I) for borrowed money, (II)
          for the deferred purchase price of property, unless the price thereof
          was payable in full within twelve months from the date on which the
          obligation was created, or (III) evidenced by notes, bonds or other
          instruments; (B) all Lease Obligations of such Person; and (C) all
          guaranties and other contingent obligations of such Person in respect
          of all indebtedness referred to in the foregoing CLAUSES (A) and (B)
          of any other Person."

     B.   The definition of "Interest Charges" set forth in Section 1.1 of the
Credit Agreement is hereby amended by deleting such definition in its entirety
and substituting in lieu thereof the following:

          ""INTEREST CHARGES" means, for any period, all expenses (net of any
          interest income earned during such period) accrued for interest
          (including imputed interest, accrued original issue discount and
          interest payable in kind) on all Indebtedness for such period
          (including Indebtedness consisting of Lease Obligations in respect of
          Capitalized Leases, but excluding Indebtedness consisting of Lease
          Obligations other than Capitalized Leases), all as determined in
          accordance with GAAP."

     C.   The definition of "Liabilities" set forth in Section 1.1 of the Credit
Agreement is hereby amended by deleting such definition in its entirety and
substituting in lieu thereof the following:

          " "LIABILITIES" means, with respect to any Person at any date as of
          which the amount thereof shall be determined, an amount equal (without
          duplication) to (A) all liabilities of such Person determined in
          accordance with GAAP PLUS (B) all Indebtedness of such Person PLUS (C)
          the aggregate amount of such Person's reimbursement obligations in
          respect of letters of credit MINUS (D) the aggregate deferred income
          tax liability of such Person."

     D.   The definition of "Net Worth" set forth in Section 1.1 of the Credit
Agreement is hereby amended by deleting the first sentence of such definition in
its entirety and substituting in lieu thereof the following first sentence:

          " "NET WORTH" means, at any date as of which the amount thereof shall
          be determined with respect to any Person, the sum of the following
          amounts which would be set forth on a balance sheet of such Person on
          such date, in each
<PAGE>
 
          case as determined in accordance with GAAP: (A) the par value (or
          values stated on the books of such Person) of the capital stock of all
          classes of such Person, other than capital stock held in the treasury
          of such Person, PLUS (B) the amount of the surplus, whether capital or
          earned, of such Person, MINUS (C) the amount which would be carried in
          the asset side of such balance sheet of such Person in respect of
          goodwill, trade names, trademarks, patents, unamortized debt issuance
          expense and other intangibles, MINUS (D) any increase in the net book
          value of fixed assets arising from a revaluation thereof after
          September 30, 1995."

     E.   The definition of "Subordinated Indebtedness" set forth in Section 1.1
of the Credit Agreement is hereby deleted in its entirety.

     F.   The definition of "Term Out Date" set forth in Section 1.1 of the
Credit Agreement is hereby amended by deleting the date "June 30, 1997" from
such definition and substituting in lieu thereof the date "June 30, 1998".

     G.   Section 7.1(f) of the Credit Agreement is hereby amended by deleting
therefrom the following phrase: "(excluding Subordinated Indebtedness)."

     H.   Section 7.2 of the Credit Agreement is hereby deleted in its entirety
and the following substituted in lieu thereof:

          " 7.2 LEVERAGE RATIO OF COMPANY. The Company shall not permit the
          ratio of Liabilities of the Company to Net Worth of the Company to
          exceed 4.50 to 1.00 as of the end of any fiscal quarter."

     I.   Section 7.5 of the Credit Agreement is hereby deleted in its entirety
and the following substituted in lieu thereof:

          "7.5  CONSOLIDATED LEVERAGE RATIO. The Ultimate Parent shall not
          permit the ratio of Consolidated Liabilities of the Ultimate Parent
          and its Subsidiaries to Consolidated Net Worth of the Ultimate Parent
          and its Subsidiaries to exceed (A) 4.50 to 1.00 at any time prior to
          the Term Out Date and (B) 4.00 to 1.00 at any time on or after the
          Term Out Date."

     J.   Section 8 (f) of the Credit Agreement is hereby deleted in its
entirety and the following substituted in lieu thereof:

          "(F)  the Ultimate Parent, the Parent, the Company or any of their
          respective Subsidiaries shall default (as principal or guarantor or
          other surety) in the payment of any principal or premium, if any, of,
          or interest or fees
<PAGE>
 
          on, any other Indebtedness to any Bank, or any other Indebtedness in
          respect of borrowed money in an aggregate principal amount of
          $10,000,000 or more (which default is in payment thereof at its stated
          maturity or shall result in such Indebtedness becoming or being
          declared due prior to the scheduled maturity thereof) or if the
          Ultimate Parent, the Parent, the Company or any of their respective
          Subsidiaries shall fail to comply (and such failure to comply has not
          been cured or waived) with any of the terms of any document evidencing
          any such Indebtedness, or any mortgage, pledge, assignment, indenture
          or other document relating thereto, and as a consequence of any of the
          foregoing, the holder of such Indebtedness shall have the right to
          declare all amounts payable with respect thereto to be due and payable
          by reason of such default prior to the scheduled maturity thereof or
          demand payment of all amounts payable in respect of any Indebtedness
          payable on demand; or

     K.   Schedules 1.1(A) and 1.1 (B) of the Credit Amendment are hereby
amended by deleting them in their entirety and substituting in lieu thereof
Schedules 1.1(A) and 1.1(B), respectively, annexed hereto.

     L.   Schedule 1.1(C) of the Credit Agreement is hereby deleted in its
entirety.

     M.  Sections 7.2 through 7.5 of the Compliance Certificate set forth in
Exhibit E to the Credit Agreement are hereby deleted and the provisions of
Exhibit A hereto are hereby substituted in lieu thereof.

     4.   CONDITIONS TO EFFECTIVENESS. Provided that no Default or Event of
Default shall then exist, this First Amendment shall be deemed to be effective
as of the date ("EFFECTIVE DATE") which is the later to occur of (a) June 28,
1996, and (b) the date on which the Administrative Agent shall have received
each of the following for the benefit of the Banks and the Agents, in form and
substance satisfactory to the Administrative Agent and the Banks:

          a.  This First Amendment to Credit Agreement duly executed and
     delivered by the Company and each of the Agents and the Banks;

          b.  The duly executed Ratification and Confirmation to Guaranty duly
     executed and delivered by the Ultimate Parent in favor of the Banks (a form
     of such Ratification and Confirmation is annexed as Exhibit B hereto) (the
     "ULTIMATE PARENT RATIFICATION");

          c.  The duly executed Ratification and Confirmation to Guaranty duly
     executed and delivered by the Parent in favor of
<PAGE>
 
     the Banks (a form of such Ratification and Confirmation is annexed as
     Exhibit C hereto) (the "PARENT RATIFICATION");

          d.  The duly executed replacement Notes, as appropriate, to evidence
     the change in each Bank's respective Commitment amount with respect to the
     Loans (forms of such replacement Notes are annexed as Exhibits D-1 through
     D-12 hereto) (collectively, the "REVISED NOTES");

          e.  True, complete and accurate copies, duly certified by an officer
     of the Company, of all documents evidencing any necessary corporate action,
     resolutions, consents and governmental approvals, if any, required for the
     execution, delivery and performance of this First Amendment, the Revised
     Notes, and any other document, instrument or agreement executed or
     delivered in connection therewith by the Company;

          f.  True, complete and accurate copies, duly certified by an officer
     of the Ultimate Parent, of all documents evidencing any necessary corporate
     action, resolutions, consents and governmental approvals, if any, required
     for the execution, delivery and performance of the Ultimate Parent
     Confirmation and any other document, instrument or agreement executed or
     delivered in connection therewith by the Ultimate Parent;

          g.  True, complete and accurate copies, duly certified by an officer
     of the Parent, of all documents evidencing any necessary corporate action,
     resolutions, consents and governmental approvals, if any, required for the
     execution, delivery and performance of the Parent Confirmation and any
     other document, instrument or agreement executed or delivered in connection
     therewith by the Parent;

          h.  An opinion of counsel to the Company, the Ultimate Parent and the
     Parent addressed to the Agents and the Banks dated as of the Effective Date
     in form and substance satisfactory to the Agents; and,

          i.  Such other documents, instruments or agreements as the Agents and
     the Banks may reasonably request.

     5.   SURRENDER OF NOTES. Each Bank receiving a Revised Note executed by the
Company, shall thereupon simultaneously surrender to the Administrative Agent
for delivery to the Company its prior Note, in each case marked "surrendered,".

     6.   REPRESENTATIONS AND WARRANTIES. In order to induce the Agents and the
Banks to enter into this First Amendment, the Company hereby represents,
warrants and certifies to each of the Agents and the Banks that as of the date
of this First Amendment and as of the Effective Date:
<PAGE>
 
          a.  no Default or Event of Default exists before and after giving
     effect to the amendment contained herein;

          b.  each and every representation and warranty contained in the Loan
     Documents is true, correct, complete and accurate with the same effect as
     if then made, except to the extent that such representations and warranties
     relate solely to an earlier date (in which case such representations and
     warranties shall have been true, correct, complete and accurate on and as
     of such earlier date); and

          c.  the Company is in compliance with all of the covenants contained
     in the Loan Documents.

     7.   FULL FORCE AND EFFECT. Except as specifically modified or amended by
the terms of this First Amendment or the Revised Notes, the other Loan Documents
and all provisions contained therein are and shall continue in full force and
effect and are hereby ratified and confirmed.

     8.   COUNTERPARTS. This First Amendment may be executed in any number of
separate counterparts, each of which shall be deemed to be an original and all
of which together shall be deemed to be one and the same instrument.

     9.   MISCELLANEOUS. This First Amendment shall be binding upon the Company
and its successors and assigns, and shall inure to the benefit of, and be
enforceable by, the Agents and the Banks and their respective successors and
assigns and shall be governed by, and construed and enforced in accordance with,
the internal laws in effect in the State of Illinois without giving effect to
principles of choice of law.

                      [INDIVIDUAL SIGNATURE PAGES FOLLOW]
<PAGE>
 
     IN WITNESS WHEREOF, this First Amendment has been duly executed and
delivered by the duly authorized officers of the parties hereto as of the date
first written above.


                                  XTRA, INC.

                                            
                           By:     /s/ Christopher P. Joyce
                                   ---------------------------------
                           Name:   Christopher P. Joyce
                           Title:  Treasurer




                           BANK OF AMERICA NATIONAL TRUST AND
                           SAVINGS ASSOCIATION, as Administrative
                           Agent

                                        
                           By:     /s/ Craig Munro                   
                                   ---------------------------------
                           Name:   Craig Munro  
                           Title:  Managing Direcor 




                           THE FIRST NATIONAL BANK OF BOSTON, as
                           Documentation Agent


                           By:     /s/ Alicia Szendiuch             
                                   ---------------------------------
                           Name:   Alicia Szendiuch 
                           Title:  Director 



                           ABN AMRO NORTH AMERICA, INC.,
                           as Agent for ABN AMRO BANK N.V.


                           By:     /s/ James E. Davis 
                                   ---------------------------------
                           Name:   James E. Davis 
                           Title:  Vice President 


                           By:     /s/ R.E. James Hunter 
                                   ---------------------------------
                           Name:   R. E. James Hunter 
                           Title:  Group Vice President 



                           BANK OF AMERICA ILLINOIS


                           By:     /s/ Craig Munro 
                                   ---------------------------------
                           Name:   Craig Munro 
                           Title:  Managing Director
<PAGE>
 
                           CORESTATES BANK, N.A.


                           By:     /s/ Verna R. Prentice
                                   ---------------------------------
                           Name:   Verna R. Prentice
                           Title:  Vice President



                           CREDIT LYONNAIS NEW YORK BRANCH


                           By:     /s/ Robert Ivosevich
                                   ---------------------------------
                           Name:   Robert Ivosevich
                           Title:  Senior Vice President



                           LTCB TRUST COMPANY


                           By:     /s/ Noboru Kubota
                                   ---------------------------------
                           Name:   Noboru Kubota
                           Title:  Senior Vice President



                           MELLON BANK, N.A.


                           By:     /s/ Inba Ponnusamy
                                   ---------------------------------
                           Name:   Inba Ponnusamy
                           Title:  Vice President



                           PNC BANK, N.A.


                           By:     /s/ Tom Colwell
                                   ---------------------------------
                           Name:   Tom Colwell
                           Title:  Vice President
<PAGE>
 
                           ROYAL BANK OF CANADA


                           By:     /s/ D.G. Calancie
                                   ---------------------------------
                           Name:   D.G. Calancie
                           Title:  Senior Manager



                           FLEET BANK, N.A.


                           By:     /s/ Robert F. Young
                                   ---------------------------------
                           Name:   Robert F. Young
                           Title:  Vice President



                           UNION BANK OF CALIFORNIA, N.A.


                           By:     /s/ Alison A. Mason
                                   ---------------------------------
                           Name:   Alison A. Mason
                           Title:  Vice President



                           THE FIRST NATIONAL BANK OF BOSTON


                           By:     /s/ Alicia Szendiuch
                                   ---------------------------------
                           Name:   Alicia Szendiuch
                           Title:  Director



                           THE FUJI BANK, LIMITED, NEW YORK BRANCH


                           By:     /s/ Gina M. Kearns
                                   ---------------------------------
                           Name:   Gina M. Kearns
                           Title:  Vice President & Manager