Police in three area jurisdictions are investigating as many as 10 store robberies in the last few weeks in which a middle-aged man armed with a sawed-off shotgun has demanded prescription drugs and money.

The man, believed to be 45 to 50 years old, usually acts alone, although the robber was accompanied by a younger man during a Nov. 10 robbery in Rockville, Montgomery County police spokesman George Ludington said yesterday.

In that robbery, a clerk and several customers at the Racquet and Jog Center were placed in a closet whose doors were sealed with duct tape, Ludington said.

The man has been linked to 10 robberies in Montgomery, Prince George's and Anne Arundel counties, according to police.

The first incident occurred Nov. 2 in Beltsville, the most recent Monday in Kensington, authorities said.

In drugstore robberies in Bowie and Bethesda, the man stole large quantities of the tranquilizer Valium and the synthetic drug Dilaudid, a habit-forming painkiller that often is used as a heroin substitute, police said.

Montgomery police have linked the man to five robberies in that jurisdiction, while Prince George's authorities are investigating four and Anne Arundel has one case, police said.

Police said no shots have been fired during the robberies, although the robber's shotgun accidentally discharged during a Nov. 6 robbery in Crofton when the man fell while running from a food store, Anne Arundel County police spokesman Dick Malloy said yesterday.

About 4:45 p.m. Monday, the man robbed the Kensington Pharmacy armed with a shotgun and a small chrome-plated pistol, Montgomery police said.

The man browsed in the store for about an hour before approaching a clerk and demanding money, police said.

The man was last seen leaving the store's parking lot in a light-colored Ford Granada, police said.