Police arrested three suspects and were looking for one other today in the Monday night beating of quarterback Joe Gilliam of the semipro Baltimore Eagles.

Gilliam was still in stable condition at the shock trauma unit of University Hospital here.

"We think it (the assault) was quite possibly drug-related," a police spokesman said. "But I'm not going to say any more."

Police said they arrested brothers Timothy Matthews, 19, and Warren Matthews, 18, and a third suspect, Edward Bright, 21.

Timothy Matthews was being held on $100,000 bond, charged with assault with intent to murder, possession with intent to distribute eight packages of herion, possession of a "small quantity" of marijuana and malicious destruction of property. A trial date was set for Sept. 11.

Warren Matthews and Bright were charged with assault with intent to murder and malicious distruction of property. No bail had been set.

A hospital spokesman said X-rays showed Gilliam suffered no serious head damage, despite the severe beating. Police said four men smashed his car windows, then beat him with two-by-fours and an iron pipe.

Gilliam had parked a company-owned car at an intersection in a seedy Baltimore neighborhood known for its drug connections, police said.

Gilliam was a quarterback with the Pittsburgh Steelers in 1972-75, but alleged drug abuse curtailed his NFL career. After completing a drug rehabilitation program in 1977, he tried out for the New Orleans Saints but failed to make the cut. He then joined the Baltimore team. One of Gilliam's colleagues said today that he was aware that Gilliam had had heroin problems, but added, "If he has a problem now, I'm not aware of it and I can't forsee him having one."

The teammate, Dan Bungori, said he and Gilliam discussed the drug problem briefly while rooming together on road trips.

"He realizes that that problem is in the past," Bungori said. "He realizes that he was definitely going nowhere in that kind of scene. And there's no question about his football talents."

Beside the team involvement, Gilliam also worked as inventory manager and general troubleshooter for the Royal Oil Corp. here, which owns the team and the car involved.