An off-duty D.C. police detective who walked in on a robbery at a jewelry store in Seabrook yesterday shot and fatally wounded a suspected holdup man with whom he exchanged gunfire, Prince George's County police said.

The dead man was identified early today as Walter Harris Terry, 19, of 3426 Dix St. NE, but police were unable to provide any details about his background.

The policeman, Richard Ragsdale, 38, a member of the D.C. police burglary and pawn investigations branch, suffered a minor wound in the incident, police said.

Officials said that at about 4 p.m., two men entered the Seabrook Jewelry and Foto Center at 9432 Lanham-Severn Rd., announced a holdup, and forced a clerk into a rear office at gunpoint.

Shortly afterward, Ragsdale, who was not in uniform, entered the store to pick up a gift he had ordered earlier, but became suspicious when he did not find a clerk at the counter.

Police said Ragsdale walked to the rear of the store to search for the clerk, but was confronted by one of the robbers, who ordered him into a back room.

Ragsdale drew his .38-caliber service revolver and exchanged shots with the man, police said. They said the man was struck in the left side of his chest, while Ragsdale was grazed on his right side.

Terry was pronounced dead at Prince George's General Hospital about 8 p.m., hospital officials said. Ragsdale, a 17-year member of the D.C. force, was treated there and released.

A second robbery suspect left the store and escaped in a car waiting in the shopping center's parking lot, police said.

The jewelry store clerk was not reported injured in the incident.

Detective Ragsdale, reached at his home last night, declined to comment on the incident, saying that he would " . . . rather speak to my own officials first."