Document:

THE INTERPUBLIC GROUP OF COMPANIES, INC.
               WORLDWIDE ADVERTISING AND MARKETING COMMUNICATIONS

       STEVEN BERNS
Vice President & Treasurer
    Tel. 212-621-5770
    Fax: 212-621-5748
  sberns@interpublic.com

                                                September 30, 2002

Citibank, N.A., as Agent for the
Lenders party to the Credit
Agreement referred to below
Two Penns Way
New Castle, Delaware 19720
Attention:  Bank Loan Syndications
Department

Ladies and Gentlemen:

         We refer to the two letter agreements (collectively, the "Letter
Agreements" and individually a "Letter Agreement"), each dated as of August 6,
2002, among the Company and the Required Lenders named therein relating to each
of the two Credit Agreements, as amended, among The Interpublic Group of
Companies, Inc., the initial lenders named therein, and Citibank, N.A. as
Administrative Agent, one for a term of 364 days the other for a term of 5
years, respectively (collectively, the "Credit Agreements" and individually a
"Credit Agreement"). Capitalized terms used but not defined herein are used with
the meanings given to those terms in the Credit Agreement.

         The Company requests that the Lenders agree to extend the termination
date of the waiver contained in each Letter Agreement to the earlier of (x)
November 14, 2002 and (y) the filing by the Company with the Securities and
Exchange Commission of restated financial statements in respect of the Event (as
defined in the Letter Agreements).

         This letter agreement, including the foregoing extension, constitutes
the entire agreement of the parties relating to the extension of the termination
date of the waivers contained in the Letter Agreements and supersedes any
previous understanding or agreement by the parties with respect thereto.

         Please indicate your agreement, as well as the agreement of each of the
Lenders named below, with the foregoing extension by having the enclosed
duplicate copy of this letter agreement executed in the space provided below by
a duly authorized representative of each of the Lenders named below and return
the same to Susan Hobart at Sherman & Sterling via facsimile at (212) 848-7179
prior to 11:00AM on October 15, 2002 and mail the original to her office at 599
Lexington Avenue, New York, NY 10022.

                                           THE INTERPUBLIC GROUP OF
                                           COMPANIES, INC.

                                           By: /s/ Steven Berns
                                               -------------------------------
                                               Name: STEVEN BERNS
                                               Title: VICE PRESIDENT & TREASURER

Confirmed and Agreed:

CITIBANK, N.A.

By: /s/ Carolyn A. Kee
    ------------------------------
Name: CAROLYN A. KEE
Title: VICE PRESIDENT

BANCA POPOLARE DI BERGAMO-CV

By: /s/ Riccardo Sora
    ------------------------------
Name: RICCARDO SORA
Title: DEPUTY GENERAL MANAGER

BANK OF AMERICA, N.A.

By: /s/ William K. Burton
    ------------------------------
Name: WILLIAM K. BURTON
Title: MANAGING DIRECTOR

BANK OF TOKYO-MITSUBISHI TRUST COMPANY

By: /s/ Spencer Hughes
    ------------------------------
Name: SPENCER HUGHES
Title: VICE PRESIDENT

BANK ONE, NA (MAIN OFFICE CHICAGO)

By: /s/ Jeffrey Lubatkin
    ------------------------------
Name: JEFFREY LUBATKIN
Title: DIRECTOR

BARCLAYS BANK PLC

By: /s/ Nicholas Bell
    ------------------------------
Name: NICHOLAS BELL
Title: DIRECTOR

BNP PARIBAS

By: /s/ Simone G. Vinocour McKeever
    -------------------------------
Name: SIMONE G. VINOCOUR McKEEVER
Title: VICE PRESIDENT

By: /s/ Arnaud Collin du Bocage
    ------------------------------
Name: ARNAUD COLLIN du BOCAGE
Title: MANAGING DIRECTOR

FLEET NATIONAL BANK

By: /s/ Thomas J. Levy
    ------------------------------
Name: THOMAS J. LEVY
Title: SENIOR VICE PRESIDENT

HSBC BANK USA

By: /s/ Johan Sorensson
    ------------------------------
Name: JOHAN SORENSSON
Title: HSBC BANK USA

ING CAPITAL LLC

By: /s/ William James
    ------------------------------
Name: WILLIAM JAMES
Title: DIRECTOR

JPMORGAN CHASE BANK

By: /s/ Thomas J. Cox
    ------------------------------
Name: THOMAS J. COX
Title: VICE PRESIDENT

KEYBANK NATIONAL ASSOCIATION

By: /s/ Lawrence A. Mack
    ------------------------------
Name: LAWRENCE A. MACK
Title: SENIOR VICE PRESIDENT

LLOYDS TSB BANK PLC

By: /s/ Richard M. Heath
    ------------------------------
Name: RICHARD M. HEATH
Title: VICE PRESIDENT

By: /s/ Lisa Maguire
    ------------------------------
Name: LISA MAGUIRE
Title: ASSISTANT VICE PRESIDENT

MIZUHO CORPORATE BANK, LTD.

By: /s/ Raymond Ventura
    ------------------------------
Name: RAYMOND VENTURA
Title: SENIOR VICE PRESIDENT

ROYAL BANK OF CANADA

By: /s/ Suzanne Kaicher
    ------------------------------
Name: SUZANNE KAICHER
Title: MANAGER

SUNTRUST BANK

By: /s/ Jennifer DeAtley
    ------------------------------
Name: JENNIFER DeATLEY
Title: ASSISTANT VICE PRESIDENT

THE NORTHERN TRUST COMPANY

By: /s/ Russ Rockenbach
    ------------------------------
Name: RUSS ROCKENBACH
Title: VICE PRESIDENT

WACHOVIA

By: /s/ Anne L. Sayles
    ------------------------------
Name: ANNE L. SAYLES
Title: DIRECTOR

WESTPAC BANKING CORPORATION

By: /s/ Lisa Porter
    ------------------------------
Name: LISA PORTER
Title: VICE PRESIDENT<Page>
                                                                     Exhibit 4.1

       COMMON STOCK            STEWART & STEVENSON                SHARES
          Number                  SERVICES, INC.            CUSIP 860342 10 4
         NYC 9995
                                                        SEE REVERSE FOR CERTAIN
                                                            DEFINITIONS AND
  INCORPORATED UNDER THE                                  NOTICE OF DENIAL OF
LAWS OF THE STATE OF TEXAS                                 PREEMPTIVE RIGHTS

THIS CERTIFIES that

is the owner of

fully paid and non-assessable shares of the Common Stock, without par value, of
                       STEWART & STEVENSON SERVICES, INC.

transferable on the books of the Corporation by the holder hereof in person or
by duly authorized attorney upon surrender of this Certificate properly
endorsed. This Certificate and the shares represented hereby are issued and
shall be subject to all of the provisions of the Restated Articles of
Incorporation, as from time to time amended, and the By-Laws of the Corporation,
as from time to time amended, copies of which are on file at the principal
office of the Corporation, to all of which the owner by acceptance hereof,
assents. This Certificate is not valid until countersigned and registered by the
Transfer Agent and Registrar.

IN WITNESS WHEREOF, the Corporation has caused the facsimile signatures of its
duly authorized officers and its facsimile seal to be affixed hereto.

      Dated

---------------------------------         ----------------------------------
SECRETARY                                 CHAIRMAN OF THE BOARD

Countersigned and Registered:

      THE BANK OF NEW YORK

By:                      Transfer Agent and Registrar
    -------------------

Authorized Signature
                     --------------------------------

                                      -1-
<Page>

                       STEWART & STEVENSON SERVICES, INC.
                      NOTICE OF DENIAL OF PREEMPTIVE RIGHTS

      The Corporation's Restated Articles of Incorporation, on file in the
Office of the Secretary of State of the State of Texas, contain a statement
denying the preemptive right of shareholders to acquire unissued or treasury
shares of the corporation. The corporation will furnish a copy of such statement
to the record holder of this certificate without charge on request to the
corporation at its principal place of business or registered office.

      The following abbreviations, when used in the inscription on the face of
this certificate, shall be construed as though they were written out in full
according to applicable laws or regulations.

<Table>
<Caption>
<S>           <C>                                <C>
TEN COM   --  as tenants in common               UNIF GIFT MIN ACT--____________ Custodian _____________
                                                                     (Cust)                  (minor)
TEN ENT   --  as tenants by the entireties                          under Uniform Gift to Minors Act

JT TEN    --  as joint tenants with right
              of survivorship and not as                             ___________________________________
              tenants in common                                                  (State)

</Table>

   Additional abbreviations may also be used though not in the above list.

      For value received, _________________________________________ hereby
sell, assign and transfer unto

Please insert Social Security or other
      identifying number of assignee

--------------------------------------

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
   (Please print or typewrite name and address including postal zip code of
                                  assignee)

--------------------------------------------------------------------------------

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                                                                   Shares of
------------------------------------------------------------------
the Common Stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint

Attorney to transfer the said stock on the books of the within-named Corporation
with full power of substitution in the premises.

Dated:
       -------------------------

                              SIGN HERE
                                        -------------------------------------
                              signature must correspond with name on face of
                              certificate without any change or alteration
                              whatever

                                      -2-
<Page>

      THIS CERTIFICATE ALSO EVIDENCES AND ENTITLES THE HOLDER HEREOF TO CERTAIN
RIGHTS AS SET FORTH IN A RIGHTS AGREEMENT BETWEEN STEWART & STEVENSON SERVICES,
INC. AND THE BANK OF NEW YORK, DATED AS OF MARCH 15,1995 (THE "RIGHTS
AGREEMENT"), THE TERMS OF WHICH ARE HEREBY INCORPORATED HEREIN BY REFERENCE AND
A COPY OF WHICH IS ON FILE AT THE PRINCIPAL EXECUTIVE OFFICES OF STEWART &
STEVENSON SERVICES, INC. UNDER CERTAIN CIRCUMSTANCES, AS SET FORTH IN THE RIGHTS
AGREEMENT, SUCH RIGHTS WILL BE EVIDENCED BY SEPARATE CERTIFICATES AND WILL NO
LONGER BE EVIDENCED BY THIS CERTIFICATE. STEWART & STEVENSON SERVICES, INC. WILL
MAIL TO THE HOLDER OF THIS CERTIFICATE A COPY OF THE RIGHTS AGREEMENT WITHOUT
CHARGE AFTER RECEIPT OF A WRITTEN REQUEST THEREFOR, AS DESCRIBED IN THE RIGHTS
AGREEMENT, RIGHTS ISSUED TO OR ACQUIRED BY ANY ACQUIRING PERSON OR ANY AFFILIATE
OR ASSOCIATE THEREOF (EACH AS DEFINED IN THE RIGHTS AGREEMENT) SHALL UNDER
CERTAIN CIRCUMSTANCES, BECOME NULL AND VOID.

                                      -3-

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