<PAGE>
                                                                     EXHIBIT 4.9
                                                                  EXECUTION COPY

                     FIRST AMENDMENT TO THE CREDIT AGREEMENT


         FIRST AMENDMENT, dated as of May 2, 2003 (the "Amendment"), to the
Credit Agreement, dated as of September 17, 2002 (as amended, supplemented or
otherwise modified from time to time, the "Credit Agreement"), among TFM, S.A.
DE C.V., a limited liability company with variable capital (sociedad anonima de
capital variable) organized under the laws of the United Mexican States (the
"Borrower"), the several Banks parties thereto, Bank of America, N.A., Comerica
Bank and Landesbank Schleswig-Holstein Girozentrale, Kiel, as Arrangers,
Standard Chartered Bank, as Arranger and Documentation Agent, and JPMorgan Chase
Bank, as Administrative Agent.

                               W I T N E S S E T H:


         WHEREAS, the Borrower, the Banks and the Administrative Agent are
parties to the Credit Agreement;

         WHEREAS, the Borrower has requested that the Banks amend the Credit
Agreement, as more fully described herein; and

         WHEREAS, the Banks are willing to agree to such amendment, but only
upon the terms and subject to the conditions set forth herein;

         NOW THEREFORE, in consideration of the premises and the mutual
covenants hereinafter set forth, the parties hereto hereby agree as follows:

         SECTION 1. Defined Terms. Unless otherwise defined herein, capitalized
terms which are defined in the Credit Agreement are used herein as therein
defined.

         SECTION 2. Amendments to Credit Agreement.

         (a) Amendments to Section 1.1. (i) The defined term "Adjusted
Consolidated Net Income" set forth in Section 1.1 of the Credit Agreement is
hereby amended by deleting the "and" immediately before clause (vi) thereof and
adding the following new clause (vii) immediately after clause (vi) thereof:

                  "and (vii) any amounts received by the Borrower in respect of
                  the VAT Refund."

                  (ii) The defined term "Consolidated Net Income" set forth in
         Section 1.1 of the Credit Agreement is hereby amended by adding
         immediately after "Consolidated Subsidiaries" the following:

                  ", excluding any amounts included in the consolidated net
                  after tax income of the Borrower and its Consolidated
                  Subsidiaries in respect of the VAT Refund,"
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                                                                               2


         (b) Amendments to Section 6.1. Section 6.1 of the Credit Agreement is
hereby amended as follows:


                  (i) by deleting the portion of the table appearing at the end
         of subsection 6.1(a) of the Credit Agreement relating to the periods
         set forth below and substituting in lieu thereof the following:

<TABLE>
<CAPTION>
                                  Period                   Ratio

<S>                                                        <C>
                            01/01/03 - 06/30/03            2.00x

                            07/01/03 - 12/31/03            2.25x

                            01/01/04 - 06/30/04            2.50x

                            07/01/04 - 12/31/04            2.75x
</TABLE>


                  (ii) by deleting the portion of the table appearing at the end
         of subsection 6.1(c) of the Credit Agreement relating to the periods
         set forth below and substituting in lieu thereof the following:


<TABLE>
<CAPTION>
                                  Period                   Ratio

<S>                                                        <C>
                            01/01/03 - 06/30/03            4.75x

                            07/01/03 - 09/30/03            4.50x

                            10/01/03 - 12/31/03            4.25x

                            01/01/04 - 03/31/04            4.00x

                            04/01/04 - 06/30/04            3.75x

                            07/01/04 - 09/30/04            3.50x

                            10/01/04 - 12/31/04            3.25x
</TABLE>


         "(c) Amendment to Section 6.3(b). Section 6.3(b) of the Credit
Agreement is hereby amended by adding the following new clause (x) immediately
after clause (ix) thereof:

                  "(x) the declaration and payment of dividends or other
distributions by the Borrower to Grupo TFM of 50% of the difference between (x)
the net cash proceeds received by the Borrower in respect of the VAT Refund and
(y) the amount paid by the Borrower in connection with that certain agreement
dated as of June 9, 1997 celebrated by The Federal Government of the United
States of Mexico, Grupo TFM, Grupo TMM and KCSI to repurchase the Capital Stock
of the Borrower pursuant to Section 6.3(b)(vii) or Section 6.3(d) hereof."

         (d) Amendment to Section 6.13. Section 6.13 of the Credit Agreement is
hereby amended by adding immediately at the end thereof the following new
Section 6.14:

                   "SECTION 6.14. Restricted Indebtedness. (a) Increase the
aggregate amount of Consolidated Indebtedness at any time from the Effective
Date through and including October

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                                                                               3



31, 2003 to an amount greater than the aggregate amount of Consolidated
Indebtedness outstanding as of March 31, 2003 or (b) create, incur, assume or
suffer to exist any Indebtedness unless the ratio of Consolidated Indebtedness
on the last day of the most recently ended fiscal quarter, after giving pro
forma effect to the incurrence of such Indebtedness as if it had been incurred
as of such date to Consolidated EBITDA on the last day of the most recently
ended fiscal quarter, is less than (i) 4.0:1.0 for any incurrence of
Indebtedness between November 1, 2003 and December 31, 2003, or (ii)
Consolidated Leverage Ratio set forth in the table in Section 6.1(c) for the
fiscal quarter during which such Indebtedness is incurred for any Indebtedness
incurred at any time after December 31, 2003.

         SECTION 3. Amendment Fee. In consideration of the agreement of the
Majority Banks to the amendments contained herein, the Borrower agrees to pay to
each Bank which executes and delivers this Amendment to the Administrative Agent
or its counsel by 12:00 noon, New York City time, on May 2, 2003, an amendment
fee in an amount equal to 0.40% of the aggregate amount of such Bank's Term
Loans outstanding on the Effective Date (as defined below). The amendment fee
shall be payable by the Borrower on the Effective Date in immediately available
funds to the Administrative Agent on behalf of the applicable Bank.

         SECTION 4. Conditions to Effectiveness of this Amendment. This
Amendment shall become effective upon the date (the "Effective Date") when the
following conditions are satisfied:

         (a) Amendment to Credit Agreement. The Administrative Agent shall have
received counterparts of this Amendment, duly executed and delivered by the
Borrower and the Majority Banks;

         (b) No Default. No Default or Event of Default shall have occurred and
be continuing on such date after giving effect to the amendments contained
herein; and

         (c) Representations and Warranties. Each of the representations and
warranties made by the Borrower in or pursuant to the Credit Agreement shall be
true and correct in all material respects on and as of the date hereof, after
giving effect to this Amendment, as if made on and as of the date hereof, except
to the extent such representations and warranties expressly relate to a specific
earlier date, in which case such representations and warranties were true and
correct as of such earlier date.

provided, that upon satisfaction or waiver of each of the foregoing conditions,
the amendments set forth in Section 2 of this Amendment shall be deemed
effective as of March 31, 2003.

         SECTION 5. Continuing Effect of the Credit Agreement. This Amendment
shall not constitute an amendment or waiver of any provision of the Credit
Agreement not expressly referred to herein and shall not be construed as an
amendment, waiver or consent to any further or future action on the part of the
Borrower that would require an amendment, waiver or consent of the Banks or
Administrative Agent. Except as expressly amended hereby, the provisions of the
Credit Agreement are and shall remain in full force and effect.
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                                                                               4



         SECTION 6. Counterparts. This Amendment may be executed by one or more
of the parties hereto on any number of separate counterparts (including by
facsimile), and all of said counterparts taken together shall be deemed to
constitute one and the same instrument.

         SECTION 7. Severability. Any provision of this Amendment which is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

         SECTION 8. Integration. This Amendment and the Credit Agreement
represent the agreement of the Borrower, the Administrative Agent and the Banks
with respect to the subject matter hereof, and there are no promises,
undertakings, representations or warranties by the Administrative Agent or any
Bank relative to the subject matter hereof not expressly set forth or referred
to herein or in the Credit Agreement.

         SECTION 9. GOVERNING LAW. THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS
OF THE PARTIES UNDER THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED AND
INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK. THE PROVISIONS
OF SECTIONS 10.13, 10.14 AND 10.16 OF THE CREDIT AGREEMENT SHALL APPLY MUTATIS
MUTANDIS TO THIS AMENDMENT AS IF SET FORTH IN FULL HEREIN.




            [THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]
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         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered by their proper and duly authorized officers as of
the day and year first above written.

                                TFM, S.A. DE C.V.


                                By:  /s/ Mario Mohar
                                     Name:  Mario Mohar
                                     Title: CEO


                                By:  /s/ Leon Ortiz
                                     Name:  Leon Ortiz
                                     Title: Finance Director



                                JP MORGAN CHASE BANK, as
                                Administrative Agent


                                By:  /s/ Linda M. Meyer
                                     Name:  Linda M. Meyer
                                     Title: Vice President
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                                BANK OF AMERICA, N.A.


                                By:  /s/ Carmen [Illegible]
                                     Name:  Carmen [Illegible]
                                     Title: Managing Director
<PAGE>
                                BBVA BANCOMER S.A.



                                By:  /s/ Manuel Arriounaga Gomez del Campo
                                     Name:  Manuel Arriounaga Gomez del Campo
                                     Title: Director Banca Corporativa


                                By:  /s/ Carlos David Velazquez Thierry
                                     Name:  Carlos David Velazquez Thierry
                                     Title: Director Banca Corporativa
<PAGE>
                                CITIBANK, N.A.



                                By:  /s/ Jose Maria Urquiza
                                     Name:  Jose Maria Urquiza
                                     Title: Vice President
<PAGE>
                                COMERICA BANK


                                By:  /s/ Myrna E. Fernandez-Lynch
                                     Name:  Myrna E. Fernandez-Lynch
                                     Title: International Lending Officer
<PAGE>
                                EXPORT DEVELOPMENT CANADA



                                By:  /s/ Bruce Millar
                                     Name:  Bruce Millar
                                     Title: Risk Management Officer


                                By:  /s/ Peter Johnston
                                     Name:  Peter Johnston
                                     Title: Financial Services Manager
<PAGE>
                                JPMORGAN CHASE BANK

                                By:  /s/ Linda M. Meyer
                                     Name:  Linda M. Meyer
                                     Title: Vice President
<PAGE>
                                LANDESBANK SCHLESWIG-HOLSTEIN
                                GIROZENTRALE, KIEL

                                By:  /s/ Michiel Munting
                                     Name:  Michiel Munting
                                     Title: Senior Vice President



                                By:  /s/ Ursula Kollex
                                     Name:  Ursula Kollex
                                     Title: Vice President
<PAGE>
                                STANDARD CHARTERED BANK


                                By:  /s/ Steve Aloupis
                                     Name:  Steve Aloupis
                                     Title: Senior Vice President


                                By:  /s/ Lawrence Fitzgerald
                                     Name:  Lawrence Fitzgerald
                                     Title: Vice President
<PAGE>
                                  WESTLB AG, NEW YORK BRANCH


                                  By:  /s/ Salvatore Battinelli
                                       Name:  Salvatore Battinelli
                                       Title: Managing Director


                                  By:  /s/ Daniel Hitchcock
                                       Name:  Daniel Hitchcock
                                       Title: Associate Director