Terrence Johnson, 16, free under $100,000 bond on charges of murdering two Prince George's County policemen last summer, was briefly sought by Prince George's police last night after one of his brothers was injured juring an argument with him, sources said.

The brother, Melvin Johnson, 18, was treated for a cut hand at Prince George's General Hospital and released about 10:30 p.m. after being struck on the head and hand with an ashtray, according to the sources. They said the incident occurred about 8 p.m.

Police were routinely dispatched to the Johnson home when the family summoned an ambulance, the source said, and a lookout for Terrence Johnson was broadcast over the police radio because the youth was no longer at the home.

Police discontinued their search after Terrence Johnson's family located him, according to the sources, who said the family declined to press charges.

Police refused to comment on the incident last night.

Johnson is free pending trial, scheduled for March 19, in the shooting deaths of county police officers Albert M. Claggett IV and James Brian Swart in the Hyattsville police station last June 26. Police said both officers were killed with Claggett's service revolver.

Melvin Johnson is expected to be a principal defense witness at the trial because he was in the police station with his brother at the time of the shootings. The brothers had been picked up by police together the night before on suspicision of larceny.

Terrence Johnson, who is charged as an adult in the police shootings, will argue at his trial that he acted in self-defense in the shooting of Claggett and was temporarily insane when Swart was shot, his attorneys have said.

Johnson is undergoing court-ordered psychiatric examination on an outpatient basis at the Clifton T. Perkins State Hospital in Jessup, Md., as a preliminary to his trial.