A General Services Administration contract supervisor and a former Maryland building contractor each pleaded guilty yesterday in U.S. District Court to a criminal charge in connection with a $500 payment the contractor made to the supervisor five years ago.

The government contended that the GSA supervisor, Francis L. Ward, had demanded $1,000 from the contractor, Irving Hurwitz, in exchange for Ward's agreement that payment orders would be processed on time for about $116,000 in renovation work that Hurwitz's Rockville company completed on a Washington Navy Yard building.

Assistant U.S. Attorney Harry R. Benner told senior Judge William B. Bryant yesterday that on July 1, 1977, Hurwitz gave Ward a personal check for $500, written out to Ward's wife, in her maiden name, with a notation on the check that said it was for "engineering fees." No other money was paid, Benner said.

Benner said the GSA eventually learned of the payment from a former employe of Hurwitz's.

Both Ward and Hurwitz, while admitting that the money was paid, disputed the prosecution's version of the facts. They contended instead that the money was intended to insure "labor peace" on the job and that nothing specific was expected in return for the payment.

Ward has been a contract monitor for GSA for 15 years and is still employed there, a GSA spokesman said. Hurwitz now lives in Coral Springs, Fla.

The two men face a possible year in jail and a $5,000 fine for their guilty pleas to one count each of supplementing the salary of a government official. Bryant scheduled sentencing for Oct. 14.