<PAGE>

                                                                     EXHIBIT 4.1

                                 FIRST AMENDMENT
                               TO ESCROW AGREEMENT

                  FIRST AMENDMENT (this "First Amendment"), dated as of August
21, 2003, by and among URS Corporation, a Delaware corporation ("Parent"), URS
Holdings, Inc., a Delaware corporation and wholly owned subsidiary of Parent
("EG&G Merger Sub"), URS-LSS Holdings, Inc., a Delaware corporation and a wholly
owned subsidiary of Parent ("Lear Merger Sub" and together with EG&G Merger Sub,
the "Merger Subs"), EG&G Technical Services Holdings, L.L.C. (the "Holder
Representative") and State Street Bank and Trust Company of California, N.A., a
national banking association (the "Escrow Agent").

                  WHEREAS, pursuant to the Agreement and Plan of Merger, dated
as of July 16, 2002 (the "Original Merger Agreement"), Carlyle-EG&G Holdings
Corp., a Delaware corporation ("EG&G" or a "Target Company"), was merged with
and into EG&G Merger Sub, and Lear Siegler Services, Inc., a Delaware
corporation ("Lear" or a "Target Company" and, together with EG&G, the "Target
Companies"), was merged with and into Lear Merger Sub (collectively, the
"Mergers");

                  WHEREAS, on the date hereof the Original Merger Agreement is
being amended as of the date hereof in order to permit Parent and the other
Parent Indemnitees (or any person claiming by or through them) to make certain
claims for damages in connection with the Merger Agreement beyond the one-year
period set forth in the Original Merger Agreement (the Original Merger
Agreement, as so amended, the "Merger Agreement");

                  WHEREAS, Parent, the Merger Subs, the Holder Representative
and the Escrow Agent desire to amend the Escrow Agreement, dated as of August
22, 2002, by and among the Parent, the Merger Subs, the Holder Representative
and the Escrow Agreement (the "Original Escrow Agreement"), in order to permit
Parent and the other Parent Indemnitees (or any person claiming by or through
them) to make certain claims against the Escrow Agreement for indemnification,
compensation or reimbursement under Article VIII of the Merger Agreement beyond
the one-year period set forth in the Original Escrow Agreement; and

                  WHEREAS, Parent has caused to be filed and declared effective
by the Securities and Exchange Commission, a shelf registration statement on
Form S-3 (No. 333-107284) (the "Shelf Registration Statement") pursuant to Rule
415 of the Securities Act of 1933, as amended (the "Act") covering the resale of
the Escrow Shares.

                  NOW, THEREFORE, in consideration of the premises and the
representations, warranties, covenants and agreements contained hereinafter set
forth, the parties hereto agree as follows:

<PAGE>

                                    ARTICLE I

                                DEFINITIONS; ETC.

                  1.1      Definitions. Capitalized terms used but not defined
herein shall have the respective meanings ascribed to them in the Original
Escrow Agreement.

                  1.2      Effect on the Original Agreement. Except as expressly
provided in this First Amendment, all of the terms, conditions, restrictions and
other provisions contained in the Original Escrow Agreement shall remain in full
force and effect. All references to the "Agreement" herein and in the Original
Escrow Agreement shall refer to the Original Escrow Agreement as amended by this
First Amendment.

                                   ARTICLE II

                                   AMENDMENTS

                  2.1      Amendment of Section 3(i). Section 3(i) of the
Original Escrow Agreement is hereby amended to read in its entirety as follows:

         The Stock Escrow Fund shall terminate on the earliest date specified as
         such by the Holder Representative, which date is both (i) specified in
         a written notice delivered by the Holder Representative to Parent and
         the Escrow Agreement at least seven (7) days prior to such date and
         (ii) no earlier than October 21, 2003 (the "Stock Escrow Fund
         Termination Date").

                  2.2      Further Amendment. The parties hereto agree,
         reasonably promptly after the date hereof, to further amend the Escrow
         Agreement to permit the Target Stockholders to sell a number of the
         Escrow Shares to be designated by the Holder Representative in
         accordance with the plan of distribution set forth in the prospectus
         supplement to the prospectus included in the Shelf Registration
         Statement, provided that the Holder Representative shall be obligated
         to cause the Target Stockholders to deposit the net proceeds of each
         sale into the Stock Escrow Fund. The parties shall cooperate in good
         faith to agree to appropriate amendments governing such release of
         Escrow Shares and deposit of net proceeds, and related changes to the
         Escrow Agreement that are appropriate in connection therewith.

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<PAGE>

                                   ARTICLE III

                             CERTAIN REPRESENTATIONS

                  3.1      Each party hereto hereby represents and warrants to
each other party that (i) it has full power and authority to execute and deliver
this instrument and to consummate the transactions contemplated hereby and (ii)
this instrument has been duly executed and delivered by such party and, assuming
this instrument constitutes a valid and binding obligation of each other party,
this instrument constitutes a valid and binding agreement of such party,
enforceable against such party in accordance with its terms.

                                   ARTICLE IV

                               GENERAL PROVISIONS

                  4.1      Interpretation. The headings contained in this First
Amendment are for reference purposes only and shall not affect in any way the
meaning or interpretation of this First Amendment.

                  4.2      Governing Law. This First Amendment shall be governed
by the laws of the State of Delaware without regard to conflicts of laws
principles.

                  4.3      Counterparts. This First Amendment may be executed in
one or more counterparts, each of which will be deemed to be an original copy of
this First Amendment and all of which, when taken together, will be deemed to
constitute one and the same agreement. Delivery of a signed counterpart by
facsimile transmission will constitute a party's due execution and delivery of
this First Amendment.

                  (Remainder of page intentionally left blank)

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                  IN WITNESS WHEREOF, the parties hereto have executed and
delivered this First Amendment as of the date first written above.

                                      URS CORPORATION

                                      /s/ Kent Ainsworth
                                      ------------------------------------------
                                          Name: Kent Ainsworth
                                          Title: Executive Vice President and
                                          C.F.O.

                                      URS HOLDINGS, INC.

                                      /s/ Kent Ainsworth
                                      ------------------------------------------
                                          Name: Kent Ainsworth
                                          Title: Executive Vice President and
                                          C.F.O.

                                      URS-LSS HOLDINGS, INC.

                                      /s/ Kent Ainsworth
                                      ------------------------------------------
                                          Name: Kent Ainsworth
                                          Title: Executive Vice President and
                                          C.F.O.

                                      EG&G TECHNICAL SERVICES HOLDINGS, L.L.C.,
                                      in its capacity as Holder Representative

                                      /s/ Joseph E. Lipscomb
                                          ----------------------------------
                                          Name: Joseph E. Lipscomb
                                          Title: Vice President

                                      STATE STREET BANK AND TRUST COMPANY OF
                                      CALIFORNIA, N.A.

                                      /s/ Paula Oswald
                                          ----------------------------------
                                          Name: Paula Oswald
                                          Title: Vice President


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