<PAGE>   1
                                                                 EXHIBIT 10.7(a)
                             MODIFICATION AGREEMENT


         THIS MODIFICATION AGREEMENT (this "Agreement") is made as of January
19, 2000, by and between: LABARGE CLAYCO WIRELESS, L.L.C., a Missouri limited
liability company ("Borrower"); and MERCANTILE BANK NATIONAL ASSOCIATION,
formerly known as Mercantile Bank of St. Louis National Association, a national
banking association ("Bank").

                              W I T N E S S E T H:

         WHEREAS, pursuant to a certain Revolving Credit executed by Borrower
and Bank on September 1, 1997 (as modified and extended, the "Revolving
Credit"), Borrower executed a certain Promissory Note payable to Bank dated
September 1, 1997, in the original principal amount of $1,000,000.00 (as
modified and extended, the "Note");

         WHEREAS, the Revolving Credit and Note are described in and secured by
a certain Security Agreement, executed by Borrower in favor of Bank on September
1, 1997, and covering the property as more particularly described therein (the
"Security Agreement");

         WHEREAS, the Revolving Credit and Note are further described in and
guaranteed by the certain Limited Guaranty executed by LaBarge, Inc. (the
"Guarantor") in favor of Bank on September 1, 1997 (the "Guaranty"); and

         WHEREAS, Revolving Credit and Note were modified and/or extended
pursuant to a certain Extension Agreement dated as of September 1, 1997, a
certain Extension Agreement dated as of September 1, 1998, a certain
Modification Agreement dated as of January 21, 1999, a certain Extension
Agreement dated as of September 1, 1999, and a certain Extension Agreement dated
as of November 30, 1999, and Borrower desires to further modify the terms of the
Revolving Credit and Note in the manner set forth herein and Bank is willing to
agree to said modification on the terms and conditions set forth herein;

         NOW, THEREFORE, in consideration of the premises, and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, Borrower and Bank hereby agree as follows:

         1. The references to "One Million and 00/100 Dollars ($1,000,000.00)"
and "$1,000,000.00" in the Revolving Credit and the Note are deleted and
substituted with "Two Million and 00/100 Dollars ($2,000,000.00)" and
"$2,000,000.00" respectively.

         2. Borrower shall maintain an annual tangible net worth for each fiscal
year (as calculated under generally accepted accounting principles consistently
applied) of at least Six Hundred Fifty Thousand and 00/100 Dollars
($650,000.00), to be calculated as of the end of each fiscal year. The failure
of Borrower to maintain said annual tangible net worth requirement shall be an
Event of Default under the Note.


                                      -1-
<PAGE>   2

         3. The Revolving Credit and Note, as hereby modified, are, and shall
continue to be, secured by the Security Agreement and Guaranty and any reference
to the Revolving Credit and Note in such documents shall hereafter be deemed to
include the Revolving Credit and Note as hereby modified.

         4. The Revolving Credit, Note and Security Agreement are, and shall
remain, the binding obligations of Borrower, and all of the provisions, terms,
stipulations, conditions, covenants and powers contained therein shall stand and
remain in full force and effect, except only as the same are herein and hereby
expressly and specifically varied or amended, and the same are hereby ratified
and confirmed, and Bank reserves unto itself all rights and privileges granted
thereunder.

         5. Borrower hereby reaffirms all representations, warranties, covenants
and agreements recited in the Revolving Credit, Note and Security Agreement as
of the date hereof, and the same are hereby adopted as representations,
warranties, covenants and agreements of Borrower herein. Borrower further
represents and warrants that it is not in default under any of its obligations
under the Revolving Credit, Note and Security Agreement and that it has full
power and authority to execute and deliver this Agreement, and that the
execution and delivery hereof has been duly authorized, and that all necessary
and proper acts have been performed or taken.

         6. Borrower agrees to pay all expenses incurred by Bank in connection
with this Agreement, including, but not limited to, Bank's legal fees. Said sums
are payable on demand and are secured by the Security Agreement and Guaranty.

         7. NOTICE REQUIRED BY SECTION 432.045 R.S. MO.: ORAL AGREEMENTS OR
COMMITMENTS TO LOAN MONEY, EXTEND CREDIT OR TO FORBEAR FROM ENFORCING REPAYMENT
OF A DEBT INCLUDING PROMISES TO EXTEND OR RENEW SUCH DEBT ARE NOT ENFORCEABLE.
TO PROTECT YOU (BORROWER(S) AND US (CREDITOR) FROM MISUNDERSTANDING OR
DISAPPOINTMENT, ANY AGREEMENTS WE REACH COVERING SUCH MATTERS ARE CONTAINED IN
THIS WRITING, WHICH IS THE COMPLETE AND EXCLUSIVE STATEMENT OF THE AGREEMENT
BETWEEN US, EXCEPT AS WE MAY LATER AGREE IN WRITING TO MODIFY IT.



                         (SIGNATURES ON FOLLOWING PAGE)



                                      -2-


<PAGE>   3



         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the day and year first above written.




                                      BORROWER:

                                      LABARGE CLAYCO WIRELESS, L.L.C.

                                      By:  /s/  Donald H. Nonnenkamp
                                           -------------------------
                                      Title: Manager






                                      BANK:


                                      MERCANTILE BANK NATIONAL ASSOCIATION

                                      By:  /s/  Jaycee D. Greene
                                           -------------------------
                                      Title: Assistant Vice President




                              CONSENT OF GUARANTOR

         Guarantor hereby joins in and consents to this Agreement and
acknowledges that the Revolving Credit and Note, as modified by this Agreement,
shall be and remain shall be and remain binding obligations of Borrower and of
Guarantor pursuant to the Guaranty.


                                      LABARGE, INC., GUARANTOR

                                      By:  /s/  Donald H. Nonnenkamp
                                           -------------------------
                                      Title: Vice President & CFO

                                      Date: January 19, 2000




                                      -3-