<PAGE>
                                                               Exhibit 10.4(c)

                        THIRD AMENDMENT TO LOAN AGREEMENT


         This Third Amendment to Loan Agreement, dated this 31st day of July,
2002, by and among Michael Baker Corporation, a Pennsylvania corporation
("MBC"), Michael Baker, Jr., Inc., a Pennsylvania corporation ("Michael Baker
Jr."), Baker/MO Services, Inc., a Texas corporation ("Baker/MO"), Baker/OTS,
Inc., a Delaware corporation ("Baker/OTS"), Baker Engineering NY, Inc., a New
York corporation ("Baker NY") (each a "Borrower" and collectively, the
"Borrowers"), Citizens Bank of Pennsylvania (assignee of Mellon Bank, N.A.), a
Pennsylvania banking institution ("Citizens"), National City Bank of
Pennsylvania, a national banking association ("NCB"), and Fifth Third Bank, a
national banking association ("Fifth Third") (each a "Bank" and collectively,
the "Banks"), and Citizens Bank of Pennsylvania, as agent for the Banks (in such
capacity, the "Agent") ("Third Amendment").

                              W I T N E S S E T H:

         WHEREAS, the Borrowers, the Banks and the Agent entered into that
certain Loan Agreement, dated September 5, 2001, as amended by that certain
First Amendment to Loan Agreement, dated February 20, 2002, as amended by that
certain Second Amendment to Loan Agreement, dated April 26, 2002 (the "Loan
Agreement"), pursuant to which, among other things, the Banks agreed to extend
credit to the Borrowers pursuant to a revolving credit facility in an aggregate
principal amount not to exceed Forty Million and 00/100 Dollars
($40,000,000.00); and

         WHEREAS, the Borrowers desire to amend certain provisions of the Loan
Agreement and the Banks and the Agent shall permit such amendments pursuant to
the terms and conditions set forth herein.

         NOW, THEREFORE, in consideration of the premises contained herein and
other valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, and intending to be legally bound hereby, the parties hereto agree
as follows:

         1. All capitalized terms used herein which are defined in the Loan
Agreement shall have the same meaning herein as in the Loan Agreement unless the
context clearly indicates otherwise.

         2. Section 1.01 of the Loan Agreement is hereby amended by deleting the
definition of "Expiry Date" and inserting the following in its stead:

                  "Expiry Date" shall mean September 30, 2004 or such earlier
                  date on which the Revolving Credit Facility Commitment shall
                  have been terminated pursuant to this Agreement.

         3. Section 6.10 of the Loan Agreement is hereby deleted in its entirety
and in its stead is inserted the following:

                           Section 6.10. Capital Expenditures. The Borrowers
                  will not, and will not permit any Subsidiary to, make or
                  commit to make, Capital Expenditures in any fiscal year
                  aggregating, for all


<PAGE>

                  Borrowers and Subsidiaries, more than Ten Million and 00/100
                  Dollars ($10,000,000.00). For purposes of this Section 6.10,
                  amounts paid with respect to Acquisitions shall not constitute
                  Capital Expenditures.

         4. The provisions of Section 2 and 3 of this Third Amendment shall not
become effective until the Agent has received this Third Amendment, duly
executed by the Borrowers and each Bank.

         5. Each Borrower hereby reconfirms and reaffirms all representations
and warranties, agreements and covenants made by it pursuant to the terms and
conditions of the Loan Agreement, except as such representations and warranties,
agreements and covenants may have heretofore been amended, modified or waived in
writing in accordance with the Loan Agreement.

         6. Each Borrower hereby represents and warrants to the Banks and the
Agent that (i) such Borrower has the legal power and authority to execute and
deliver this Third Amendment, (ii) the officers of such Borrower executing this
Third Amendment have been duly authorized to execute and deliver the same and
bind such Borrower with respect to the provisions hereof, (iii) the execution
and delivery hereof by such Borrower and the performance and observance by such
Borrower of the provisions hereof and of the Loan Agreement and all documents
executed or to be executed therewith, do not violate or conflict with the
organizational agreements of such Borrower or any Law applicable to such
Borrower or result in a breach of any provision of or constitute a default under
any other agreement, instrument or document binding upon or enforceable against
such Borrower, and (iv) this Third Amendment, the Loan Agreement and the
documents executed or to be executed by such Borrower in connection herewith or
therewith constitute valid and binding obligations of such Borrower in every
respect, enforceable in accordance with their respective terms.

         7. Each Borrower represents and warrants that (i) no Event of Default
exists under the Loan Agreement, nor will any occur as a result of the execution
and delivery of this Third Amendment or the performance or observance of any
provision hereof, (ii) the Schedules attached to and made a part of the Loan
Agreement, as amended by this Third Amendment (if applicable), are true and
correct in all material respects as of the date hereof, and (ii) it presently
has no known claims or actions of any kind at Law or in equity against the Banks
or the Agent arising out of or in any way relating to the Loan Documents.

         8. Each reference to the Loan Agreement that is made in the Loan
Agreement or any other document executed or to be executed in connection
therewith shall hereafter be construed as a reference to the Loan Agreement as
amended hereby.

         9. The agreements contained in this Third Amendment are limited to the
specific agreements made herein. Except as amended hereby, all of the terms and
conditions of the Loan Agreement shall remain in full force and effect. This
Third Amendment amends the Loan Agreement and is not a novation thereof.

         10. This Third Amendment may be executed in any number of counterparts
and by the different parties hereto on separate counterparts each of which, when
so executed, shall be


                                     - 2 -
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deemed to be an original, but all such counterparts shall constitute but one
and the same instrument.

         11. This Third Amendment shall be governed by, and shall be construed
and enforced in accordance with, the Laws of the Commonwealth of Pennsylvania
without regard to the principles of the conflicts of law thereof. Each Borrower
hereby consents to the jurisdiction and venue of the Court of Common Pleas of
Allegheny County, Pennsylvania and the United States District Court for the
Western District of Pennsylvania with respect to any suit arising out of or
mentioning this Third Amendment.


                           [INTENTIONALLY LEFT BLANK]




                                     - 3 -
<PAGE>




                  IN WITNESS WHEREOF, and intending to be legally bound, the
parties hereto have caused this Third Amendment to be duly executed by their
duly authorized officers as of the date above written.

<TABLE>
<S>                                                  <C>
Attest:                                              Michael Baker Corporation

By: /s/ H. James McKnight                            By: /s/ William P. Mooney
   --------------------------------------------         -------------------------------------

Name: H. James McKnight                              Name: William P. Mooney
     ------------------------------------------           -----------------------------------

Title: Exec VP, General Counsel & Secretary          Title: Executive Vice President
      -----------------------------------------            ----------------------------------


Attest:                                              Michael Baker, Jr., Inc.

By: /s/ H. James McKnight                            By: /s/ William P. Mooney
   --------------------------------------------         -------------------------------------

Name: H. James McKnight                              Name: William P. Mooney
     ------------------------------------------           -----------------------------------

Title: Exec VP, General Counsel & Secretary          Title: Executive Vice President
      -----------------------------------------            ----------------------------------


Attest:                                              Baker/MO Services, Inc.

By: /s/ H. James McKnight                            By: /s/ William P. Mooney
   --------------------------------------------         -------------------------------------

Name: H. James McKnight                              Name: William P. Mooney
     ------------------------------------------           -----------------------------------

Title: Exec VP, General Counsel & Secretary          Title: Executive Vice President
      -----------------------------------------            ----------------------------------


Attest:                                              Baker/OTS, Inc.

By: /s/ H. James McKnight                            By: /s/ William P. Mooney
   --------------------------------------------         -------------------------------------

Name: H. James McKnight                              Name: William P. Mooney
     ------------------------------------------           -----------------------------------

Title: Exec VP, General Counsel & Secretary          Title: Executive Vice President
      -----------------------------------------            ----------------------------------


Attest:                                              Baker Engineering NY, Inc.

By: /s/ H. James McKnight                            By: /s/ William P. Mooney
   --------------------------------------------         -------------------------------------

Name: H. James McKnight                              Name: William P. Mooney
     ------------------------------------------           -----------------------------------

Title: Exec VP, General Counsel & Secretary          Title: Executive Vice President
      -----------------------------------------            ----------------------------------


</Table>



<PAGE>
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<S>                                                  <C>
                                                     Citizens Bank of Pennsylvania, as Agent
                                                     and for itself as a Bank

                                                     By: /s/ John J. Ligday Jr.
                                                        -------------------------------------

                                                     Name: John J. Ligday Jr.
                                                          -----------------------------------

                                                     Title: Vice President
                                                           ----------------------------------


                                                     National City Bank of Pennsylvania
                                                     By: /s/ Susan J. Dimmick
                                                        -------------------------------------

                                                     Name: Susan J. Dimmick
                                                          -----------------------------------

                                                     Title: Vice President
                                                           ----------------------------------


                                                     Fifth Third Bank

                                                     By: /s/ C.S. Helmeci
                                                        -------------------------------------

                                                     Name: Christopher S. Helmeci
                                                          -----------------------------------

                                                     Title: Vice President
                                                           ----------------------------------

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