A District officer was found guilty by a D.C. Superior Court jury yesterday of beating a Silver Spring man in April 1979 while the latter was being held on a disorderly conduct charge at a police station.

The jury deliberated for three days before finding Tommy C. Musgrove, 26, of 12603 Lampton La., Oxon Hill, guilty of simple assault on Michael Morris, 22, of 404 Hensdale Ct.

Judge Gladys Kessler, who could sentence Musgrove to one year in jail, scheduled sentencing for June 27.

According to testimony, Morris was arrested for disorderly conduct at the Trailways bus station at 12th Street and New York Avenue NW and taken to the First District substation cellblock in Southeast Washington.

Assistant U.S. Attorney Jay B. Stephens contended that Musgrove entered the cellblock and assaulted Morris with a blackjack after Morris had refused to give police his social security number and had spat on the officer.

Morris was treated at D.C. General Hospital for a cut over his right eye and numerous bruises on his head, according to evidence.

Musgrove testified that he walked past the fingerprinting room and saw Morris struggling with Sgt. Freddie Moss.

Musgrove said Morris struck at him, then spat on him. Musgrove testified he punched Morris once.