<PAGE>   1

                                                                    EXHIBIT 4.4


                 TRANSPORTATION MANUFACTURING OPERATIONS, INC.

                                AMENDMENT NO. 3
                                       to
                                CREDIT AGREEMENT

                         Dated as of September 25, 1997

        This Amendment No. 3 to Credit Agreement (this "Amendment") is dated as
of September 25, 1997 and entered into by and among TRANSPORTATION
MANUFACTURING OPERATIONS, INC., a Delaware corporation (the "Borrower"), the
banks set forth on the signature pages hereof (collectively, the "Lenders" and
individually, a "Lender"), and THE FIRST NATIONAL BANK OF CHICAGO, as
Administrative Agent for the Lenders.

                                R E C I T A L S:

        A.  The Borrower, certain Subsidiaries of the Borrower, as guarantors
(the "Guarantors"), the Lenders (other than Allied Irish Bank, p.l.c., Cayman
Islands Branch ("Allied Irish Bank")) and the Administrative Agent are parties
to that certain Credit Agreement dated as of September 30, 1996, as amended by
Amendment No. 1 thereto dated as of December 17, 1996 and Amendment No. 2
thereto dated as of May 23, 1997 (the "Credit Agreement").  Capitalized terms
used herein and not otherwise defined herein shall have the meanings attributed
to such terms in the Credit Agreement.

        B.  The Borrower has requested that the aggregate Commitments under the
Credit Agreement be increased to $170,000,000, and the parties intend that
Allied Irish Bank become a party to the Credit Agreement as a Lender.

        C.  The Borrower has entered into Stage I of the transaction (the
"Transaction") described in Exhibit A attached to the Waiver and Release dated
August 15, 1997, among the Borrower, the Majority Lenders and the Agent (the
"Waiver").  As part of Stage I of the Transaction, in addition to the
capitalization described in paragraph 2 of Exhibit A to the Waiver, the
Borrower caused a letter of credit to be issued for the Borrower's account and
for the benefit of General Electric Capital Corporation, as a condition of its
credit agreement with MCII Funding Inc. ("MFI"), in the amount of $5,000,000 to
cover credit losses on loans, leases and other receivables purchased by MFI and
to support MFI's obligations under such credit agreement.  The Borrower still
contemplates the subsequent investment in equity capital of MCII Financial
Services Inc. in Stage II and/or one or more subsequent stages of the
Transaction, as described in Exhibit A to the Waiver.

        ACCORDINGLY, in consideration of the premises and the agreements and
provisions contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

        Section 1.  AMENDMENTS TO CREDIT AGREEMENT.



<PAGE>   2


        Effective as of the Amendment Effective Date (as defined below) and
subject to the satisfaction of the conditions precedent set forth in Section 3
below, the Credit Agreement is hereby amended as follows:

        (a)  The definition of "Lenders" set forth in Section 1.01 of the
Credit Agreement is amended in its entirety to read as follows:

             "Lenders" means (a) each of the lenders listed on the signature
        pages hereof and each Eligible Assignee that shall become a party
        hereto pursuant to Section 8.07 or pursuant to an amendment to this
        Agreement and (b) the Swing Line Bank.

        (b)  The first sentence of Section 2.01 of the Credit Agreement is
amended in its entirety to read as follows:

             Subject to the terms and conditions of this Agreement and in
        reliance upon the representations and warranties of the Borrower herein
        set forth, each Lender severally agrees to lend to the Borrower from
        time to time during the period on and after the Effective Date to but
        excluding the Termination Date, Advances in an aggregate outstanding
        principal amount not at any time exceeding the amount set opposite such
        Lender's name on SCHEDULE 2.01 hereto as of the effective date of
        Amendment No. 3 to this Agreement, or, if such Lender has entered into
        any Assignment and Acceptance after such date, set forth for such
        Lender in the Register maintained by the Administrative Agent pursuant
        to Section 8.07(c), as such amount may be reduced pursuant to Section
        2.06 (such Lender's "Commitment").

        (c)  Section 2.04(a) of the Credit Agreement is amended by adding at
the end thereof the following:

             From and after the effective date of Amendment No. 3 to this
        Agreement, the letter of credit issued by The First National Bank of
        Chicago ("First Chicago") and described on SCHEDULE 2.04(a) hereto (the
        "Existing Letter of Credit") shall be deemed to constitute a Letter of
        Credit issued by First Chicago as the Issuing Lender, and the Lenders
        shall be deemed irrevocably to have purchased a ratable participation
        therein, all pursuant to this Section 2.04, except that the third
        sentence of this Section 2.04(a) shall not apply to the Existing Letter
        of Credit.  A letter of credit fee shall accrue with respect to the
        Existing Letter of Credit as provided in Section 2.04(e)(ii) from and
        after the effective date of Amendment No. 3 to this Agreement.

        (d)  Section 5.02(c)(iv) of the Credit Agreement is amended by deleting
the second proviso thereto in its entirety and substituting therefor the
following:

             provided, further, that such aggregate outstanding amount may
        include up to $25,000,000 of Investments by the Borrower in MCII
        Financial Services Inc. 


                                     -2-

<PAGE>   3


        ("MFS"), an entity formed for purposes of operating as a finance        
        company, through its Subsidiary, MCII Funding Inc. ("MFI"), and in
        which members of the Gomez Flores family and Dina or any of its
        Subsidiaries may also be investors, which Investments may consist of
        (x) up to $20,000,000 of debt or equity interests (or any combination
        thereof) issued by MFS, the consideration for which may be cash or
        other property valued at fair market value, and (y) a letter of credit
        in an amount up to $5,000,000 issued for the account of the Borrower
        and for the benefit of MFI or its lender to cover credit losses on
        loans, leases and other receivables purchased by MFI and to support
        MFI's obligations to such lender;

        (e)  Section 5.02(e)(iv) of the Credit Agreement is amended by deleting
the word "Newco" therefrom and substituting therefor "MCII Funding Inc."

        (f)  The Credit Agreement is amended by deleting SCHEDULE 1.01 thereto
in its entirety and substituting therefor AMENDED SCHEDULE 1.01 in the form
attached hereto and by adding thereto a new SCHEDULE 2.01 and a new SCHEDULE
2.04(a) in the respective forms attached hereto.

        Section 2.  ALLIED IRISH BANK AS A LENDER; SANWA BANK AS AN EXITING
LENDER.

        (a)  As of the Amendment Effective Date, Allied Irish Bank shall be
bound by the terms of the Credit Agreement, as amended hereby, and shall have
all of the rights and obligations of a Lender under the Loan Documents.  Allied
Irish Bank hereby: (i) agrees that it will perform in accordance with their
terms all of the obligations which by the terms of the Loan Documents are
required to be performed by it as a Lender and (ii) confirms that it has
delivered to the Borrower and the Administrative Agent forms prescribed by the
Internal Revenue Service certifying that it is entitled to receive payments
under the Loan Documents without deduction or withholding of any United States
federal income taxes.

        (b)  As of the Amendment Effective Date, new Advances made by the
Lenders (other than The Sanwa Bank, Limited, Chicago Branch ("Sanwa Bank")) on
such date shall be used, in whole or in part, to repay existing Advances
outstanding on such date, and from and after the Amendment Effective Date and
payment to Sanwa Bank of all amounts due and payable to it under the Credit
Agreement, Sanwa Bank shall not be a Lender under the Credit Agreement, as
amended hereby, and shall be released from all obligations thereunder whether
heretofore or hereafter arising.

        Section 3.  CONDITIONS TO EFFECTIVENESS.

        This Amendment shall become effective as of the date (the"Amendment
Effective Date") of receipt by First Chicago, as the new Administrative Agent,
of the following items:

        (i)   Counterparts of this Amendment duly executed by the Borrower and
     the Lenders and of the Consent attached hereto duly executed by the
     Guarantors.


                                     -3-


<PAGE>   4


        (ii)  Promissory Notes payable to the order of the respective Lenders
     in the amounts of their respective Commitments under the Credit Agreement,
     as amended hereby, and executed and delivered by the Borrower (the "New
     Notes").

        (iii) Resolutions of the Board of Directors of the Borrower approving
     and authorizing the execution, delivery and performance of this Amendment
     and the New Notes, certified as of the date hereof by its Secretary or an
     Assistant Secretary as being in full force and effect without modification
     or amendment.

        (iv)  Such other documents as the Administrative Agent or any Lender
     may reasonably request.

As a further condition to effectiveness, as of the Amendment Effective Date the
Administrative Agent shall have received for the account of the Lenders all
accrued interest on outstanding Advances, together with amounts owing in
respect of indemnification obligations pursuant to Section 8.04(D) of the
Credit Agreement, all accrued letter of credit fees pursuant to Section 2.04(e)
of the Credit Agreement, and all accrued facility fees pursuant to Section
2.05(a) of the Credit Agreement, in each case accrued to, but not including,
the Amendment Effective Date.

        Section 4.  REPRESENTATIONS AND WARRANTIES OF BORROWER.

        To induce the Lenders to enter into this Amendment and to amend the
Credit Agreement as provided herein, the Borrower hereby represents and
warrants that:

        (a)  The Borrower has full power, authority and legal right to execute,
deliver and perform this Amendment, the Credit Agreement as amended hereby and
the New Notes, and has duly executed and delivered this Amendment and the New
Notes.

        (b)  This Amendment, the Credit Agreement as amended hereby and the New
Notes are the legal, valid and binding obligations of the Borrower enforceable
against the Borrower in accordance with their respective terms, in each case as
enforceability may be subject to the effect of applicable bankruptcy,
insolvency, arrangement, moratorium and other similar laws affecting creditors'
rights generally and to the application of general principles of equity.

        (c)  The execution, delivery and performance of this Amendment and the
New Notes by the Borrower do not require any governmental registrations or
filings or approvals and do not and will not violate or contravene any law or
any order of any court or governmental agency or any indenture, agreement or
other instrument, including, without limitation, with respect to the Senior
Notes, to which the Borrower or any of the Guarantors is party or by which any
of them or any of their respective properties may be bound.

        (d)  No event has occurred and is continuing or will result from the
execution and delivery of this Amendment that constitutes an Event of Default
or Potential Event of Default.


                                     -4-


<PAGE>   5

        Section 5.  REFERENCE TO AND EFFECT ON THE CREDIT AGREEMENT AND OTHER
LOAN DOCUMENTS.

        (a)  From and after the Amendment Effective Date, each reference in any
Loan Document to the Credit Agreement shall mean and be a reference to the
Credit Agreement as amended hereby.

        (b)  The Credit Agreement, as amended hereby, and all other Loan
Documents shall remain in full force and effect, and are hereby ratified and
confirmed.

        (c)  Except as expressly provided herein, the execution, delivery and
effectiveness of this Amendment shall not operate as a waiver of any right,
power or remedy of the Administrative Agent, the Lenders, the Swing Line Bank
or any Issuing Lender, nor constitute a waiver of any provision of the Credit
Agreement or any other Loan Document.

        Section 6.  GOVERNING LAW.  This Amendment shall be governed by and
construed in accordance with the internal laws (as opposed to the conflict of
law provisions) of the State of Illinois.

        Section 7.  HEADINGS.  Section headings in this Amendment are included
herein for convenience of reference only and shall not constitute a part of
this Amendment for any other purpose.

        Section 8.  COUNTERPARTS.  This Amendment may be executed by one or
more of the parties to the Amendment on any number of separate counterparts and
all of said counterparts taken together shall be deemed to constitute one and
the same instrument.  Signature pages may be detached from multiple separate
counterparts and attached to a single counterpart so that all signature pages
are physically attached to the same document.

        IN WITNESS WHEREOF, this Amendment has been duly executed and delivered
on the date first above written.

                                  TRANSPORTATION MANUFACTURING             
                                   OPERATIONS, INC.                        
                                                                           
                                  By: /s/ Guillermo Kareh Aarun
                                  Print Name:  Guillermo Kareh Aarun       
                                  Title: Chief Executive Corporate Officer 
                                                                           
                                  THE FIRST NATIONAL BANK OF CHICAGO,      
                                  as a Lender and as Administrative Agent  
                                                                           
                                  By: /s/ H. Antonio Mesones
                                  Name:  H. Antonio Mesones
                                  Title: International Banking Officer

                              

                                     -5-


<PAGE>   6


                                  THE BANK OF NEW YORK, as a Co-Agent and   
                                       as a Lender                          
                                                                            
                                  By:  /s/ John R. Ciulla
                                       Name:  John R. Ciulla
                                       Title: Assistant Vice President
                                                                            
                                                                            
                                  KEYBANK NATIONAL ASSOCIATION,             
                                       as a Co-Agent and as a Lender        
                                                                            
                                  By:  /s/ Lawrence A. Mack
                                       Name:  Lawrence A. Mack
                                       Title: Vice President
                                                                            
                                                                            
                                  COMERICA BANK, as a Lender                
                                                                            
                                  By:  /s/ Richard C. Northrup III
                                       Name:  Richard C. Northrup III
                                       Title: Assistant Vice President
                                                                            
                                                                            
                                  HUNTINGTON NATIONAL BANK,                 
                                       as a Lender                          
                                                                            
                                  By:  /s/ Thomas Myers
                                       Name:  Thomas Myers
                                       Title: Vice President
                                                                            
                                                                            
                                  BANK OF HAWAII, as a Lender               
                                                                            
                                  By:  /s/ Donna R. Parker
                                       Name:  Donna R. Parker
                                       Title: Vice President
                                                                            
                                                                            
                                  NATIONSBANK, N.A., as a Lender            
                                                                            
                                  By:  /s/ Valerie C. Mills
                                       Name:  Valerie C. Mills
                                       Title: Sr. Vice President




                                     -6-


<PAGE>   7


                                  THE SUMITOMO BANK, LIMITED,               
                                       as a Lender                          
                                                                            
                                  By:  /s/ Brian J. Cushing
                                       Name:  Brian J. Cushing
                                       Title: Vice President
                                                                            
                                  By:  /s/ Thomas A. Garza
                                       Name:  Thomas A. Garza
                                       Title: Vice President
                                                                            
                                                                            
                                  ALLIED IRISH BANK, P.L.C., CAYMAN ISLANDS 
                                       BRANCH, as a Lender                  
                                                                            
                                  By:  /s/ W.J. Strickland
                                       Name:  W.J. Strickland
                                       Title: Senior Vice President
                                                                            
                                  By:  /s/ Tracey Duffy
                                       Name:  Tracey Duffy
                                       Title: Assistant Vice President
                                                                            
                                                                            
                                  THE SANWA BANK, LIMITED, CHICAGO          
                                       BRANCH, as an exiting Lender         
                                                                            
                                  By:  /s/ Gordon R. Holtley
                                       Name:  Gordon R. Holtley
                                       Title: Vice President and Manager









                                     -7-


<PAGE>   8


                             AMENDED SCHEDULE 1.01

                APPLICABLE LENDING OFFICES AND NOTICE ADDRESSES

<TABLE>
<CAPTION>

INSTITUTION                 DOMESTIC LENDING OFFICE             EURODOLLAR LENDING OFFICE
<S>                         <C>                                 <C>
The First National Bank     The First National Bank of Chicago  The First National Bank of Chicago
 of Chicago                 One First National Plaza            One First National Plaza
                            Chicago, IL  60670                  Chicago, IL  60670
                            Telephone: 312-732-1301             Telephone: 312-732-1301
                            Telecopy:   312-732-1775            Telecopy:   312-732-1775
                            Attn:  Antonio Mesones              Attn:  Antonio Mesones
                            Reference: Transportation           Reference: Transportation
                             Manufacturing Operations, Inc.      Manufacturing Operations, Inc.


Allied Irish Bank, p.l.c.,  Allied Irish Bank, p.l.c.,          Allied Irish Bank, p.l.c.,
 Cayman Islands Branch       Cayman Islands Branch               Cayman Islands Branch
                            405 Park Avenue                     405 Park Avenue
                            New York, NY 10022                  New York, NY 10022
                            Telephone: 212-339-8018             Telephone: 212-339-8018
                            Telecopy:   212-339-8007            Telecopy:   212-339-8007
                            Attn:  Marcia Meeker                Attn:  Marcia Meeker
                            Reference: Transportation           Reference: Transportation
                             Manufacturing Operations, Inc.      Manufacturing Operations, Inc.
</TABLE>









                                     -8-



<PAGE>   9


                                 SCHEDULE 2.01

                                  COMMITMENTS



<TABLE>
<CAPTION>

LENDER                                              COMMITMENT
<S>                                               <C>
The First National Bank of Chicago                $ 27,600,000
                                                              
KeyBank National Association                        25,900,000
                                                              
The Bank of New York                                23,100,000
                                                              
Comerica Bank                                       20,000,000
                                                              
Huntington National Bank                            19,800,000
                                                              
Bank of Hawaii                                      15,000,000
                                                              
The Sumitomo Bank, Limited                          15,000,000
                                                              
NationsBank, N.A.                                   13,600,000
                                                              
Allied Irish Bank, p.l.c., Cayman Islands Branch    10,000,000
                                                              
                                                  ------------            
                                           Total  $170,000,000
</TABLE>







                                     -9-



<PAGE>   10


                                SCHEDULE 2.04(a)

                           EXISTING LETTER OF CREDIT



<TABLE>
<CAPTION>
                    LETTER OF                EXPIRATION
ISSUER              CREDIT NO.  FACE AMOUNT     DATE       BENEFICIARY
<S>                 <C>         <C>          <C>           <C>
The First National  365099      $5,000,000   9/11/98       General Electric
 Bank of Chicago                             (with annual   Capital Corporation,
                                             extensions)    as Agent
</TABLE>


















                                     -10-



<PAGE>   11

                                    CONSENT



        Each of the undersigned, as a Guarantor under the Subsidiary Guaranty
dated as of October 1, 1996  (the "Guaranty") in favor of the Agent for the
benefit of the Lenders parties to the Credit Agreement referred to in the
foregoing Amendment, hereby consents to said Amendment and hereby confirms and
agrees that notwithstanding the effectiveness of said Amendment, the Guaranty
is, and shall continue to be, in full force and effect and is hereby confirmed
and ratified in all respects.


Dated: September 25, 1997        BUSLEASE, INC.
                                 HAUSMAN BUS SALES, INC.
                                 MOTOR COACH INDUSTRIES, INC.
                                 MOTOR COACH INDUSTRIES-CHINA, INC.
                                 TRANSIT BUS INTERNATIONAL, INC.
                                 CUSTOM ASSETS CORP.
                                 TRANSPORT TECHNOLOGY CORPORATION
                                 UNIVERSAL COACH PARTS, INC.


                                 By:      /s/ Guillermo Kareh Aarun
                                    -------------------------------------
                                 Print Name:  Guillermo Kareh Aarun
                                 Title: Chief Executive Corporate Officer















                                     -11-