A 21-year-old man has been charged with committing six sexual assaults in the Hyattsville area during the past 18 months, Prince George's County police said yesterday.

Gary A. Stephenson, of 1521 Madison St., Hyattsville, was arrested late Tuesday after he went to police headquarters for questioning about the attacks, police spokesman Cpl. Bruce Gentile said. Stephenson was charged with four counts of first-degree sex offense and two counts of first-degree rape, he said.

Five of the attacks occurred between January and August 1985, Gentile said, and all six were on a Tuesday or Wednesday. The most recent attack occurred June 3 in the 1500 block of Madison Street in Hyattsville, police said, the same block in which Stephenson lives.

The women victims -- who are in their late teens or early twenties -- had given the same description of their assailant: a white male with a stocky build and long hair in his early twenties, Gentile said.

In all of the attacks, Gentile said, the assailant produced a handgun. He said that police have not recovered a weapon.

"We were stymied because the attacks stopped last August," Gentile said. "We still don't know where [the attacker] was between the attack last August and the one last week or why the attacks stopped."