Two more former General Services Administration office supply store managers and a U.S. Navy employe pleaded guilty here yesterday to defrauding the government in the GSA bribery scandal.

A total of eight persons have now been convicted in a scheme in which GSA supply store manager accepted bribes from office supply firms doing business with GSA. In return, the store managers allowed the supply firms to be paid by GSA for supplies that were never delivered.

All eights defendants are cooperating with federal prosecutors here, who are attempting to trace the corruption higher up in GSA. Sentencing of the eight has been put off for several months.

The three who pleaded guilty yesterday are:

Roger Dale Witt, 29, of District Heights, who was manager of the GSA supply store in the Department of Housing and Urban Development.

Johnie J. Sykes, 32, of Oxon Hill, who was manager of the GSA supply store in the Federal Building at 800 Independence Ave.

Francis Proctor, 50, of Washington who worked for the Navy Bureau of Medicine and Surgery in Arlington and cooperated in the scheme by signing for supplies his office never received from GSA.

Sykes admitted to federal Judge Frank A. Kaufman that he accepted airline tickets to Georgia, liquor, car equipment and repairs, and clothing from an office supply firm. Wilt told Judge Edward S. Northrop that he took car tires, a rifle and a lawn mower, among other items.

Prosecutors said they would recommend light sentences for the men in exchange for their continued cooperation in the investigation.