A suspected holdup man and two bystanders were wounded by gunfire at a Prince George's County shopping center yesterday when an off-duty D.C. police officer attempted to halt the suspect.

The 18-year-old suspect was wounded in the back as he emerged from the Chillum Liquor Store in the Riggs-Chillum Shopping Center by a shot fired by the officer.

County police said several hours after the incident it had not been determined whether the suspect, who was carrying a shotgun, opened fire and that they did not know whether the suspect or the officer fired the shots that wounded the bystanders, a 71-year-old man and a 12-year-old boy.

The robbery suspect and three alleged accomplices were arrested.

County police gave this account of the incident:

William Muse, the off-duty D.C. policeman, was in the liquor store when a youth entered with a shotgun and announced a holdup. As a cashier handed over cash, Muse slipped outside and waited behind a telephone booth, his service revolver drawn.

When the youth ran from the store, Muse ordered him to halt, then when he refused, fired an undetermined number of shots.

Although wounded, the youth ran around a corner of the shopping center at 5800 Eastern Ave. and got into a car, which sped away.

The car was stopped a short time later by D.C. police at Chillum Road and Twin Oaks Drive in Chillum.

Craig Steven Brooks, the youth suspected of robbing the sotre, was taken from that location to Prince George's General Hospital, where he was reported in fair condition with a back wound.

One of the bystanders wounded when the shooting broke out, Walter Thomas, 71, of 1925 Seventh St. NE, was listed in fair condition at Washington Hospital Center last night suffering from a wound to his right shoulder.

The other wounded bystander, George Powell 12, of 642 Nicholson St. NE, was treated for an ankle wound at Washington Adventist Hospital and released.

Brooks was charged with armed robbery and assault with a deadly weapon. Three persons also were charged with armed robbery in the liquor store holdup. They were identified as Leslie Lattisaw, 23 of 5416 Eighth St. NE, Arthur Keeling, 23, of 3410 Oglethorpe Dr. NE, and a 16-year-old juvenile.

Lattisaw, said to be the driver of the car, the 16-year-old and Brooks were arrested when the car was stopped, according to Prince George's police.

Keeling, the owner of the car, was arrested later at his home, police said.

Muse is a patrolman assigned to the 4th District -- the upper Georgia Avenue corridor. An investigation of the shooting is being conducted by both Prince George's and D.C. police.