Bladensburg police say they now believe a Polish immigrant killed a city police sergeant in apparent self-defense may have been making a confused attempt to save the sergeant's life.

City police and friends of Jerzy Bieganowski say he admired and befriended policemen and must have thought he was pulling a gun on a burglar when he placed his pistol to the head of Sgt. Joseph G. Marquis Jr. about 2:20 a.m. Wednesday morning.

Marquis was crouched behind his car door holding a shotgun in the dark outside the Golden Cue Pool Hall at 4821 Annapolis Rd. as the sergeant called for men he thought were burglars to come out of the pool hall.

Bieganowski, apparently attracted by the police cars surrounding the pool hall as he drove from working the night shift at the Bladensburg Mobil Service Station had jumped out to help.

However, Robert Saslaw, the manager of the Crossroads Club in Bladensburg, who had accompanied his friend Marquis in responding to a silent alarm in the pool hall saw Bieganowski with his gun on Marquis, jumped from his parked van and pushed Bieganowski away.

It was too dark to see faces, although Bieganowski knew Marquis and had occasionally worked on his car. Bieganowski whirled and fired one shot at his assailant - Saslaw. He missed, and Marquis, seeing Bieganowski shoot, fired one round with his shotgun.

Bieganowski, a 38-year-old gas station attendant who immigrated to the United States in 1961, died immediately.

"I know for certain even though I wasn't there that Jerry thought he was going to help a policeman," Mark Bobinger, a D.C. policeman and a friend of Bieganowski's, said yesterday. "He loved policeman, always said he wanted to be one. I'd swore on a stack of bibles that he thought he was going after a burglar."

Bladensburg police chief Lyon J. Chapman supported Bobinger's theory. "I would say that's very possible, extremely possible," he said, "Bieganowski probably thought he was going after a burglar.

"Our men frequently stopped in his gas station, especially late at night when all the city gas stations were closed. He was always extremely friendly and helpful. In fact I would say he was more than helpful. He liked all the men."

After being held up at the gas station about six weeks ago, Bieganowski had begun to carry a .38-caliber revolver. He roomed in Colmar Manor, living with Mary E. Curtis and her 22-year-old son, Joe, at 4209 Newton St.

He had no money at the time of his death. Bob Ketner, owner of the gas station at 5803 Annapolis Rd. where he worked, has taken up a collection to pay for the funeral. Among those contributing to the fund, according to Chapman, will be members of the Bladensburg Police Department.

He will be buried Monday at noon at the Washington Cemetery on Suitland Rd.

"Jerry always had friends because he liked people so much," Mrs. Curtis said. "He had lived with us for over a year and now I feel like I've lost a son. There was nothing he wouldn't do to help someone.

"I know when he went out of that car he was trying to help a policeman," she added. "Sgt. Marquis was his friend. If he had known it was him, he never would have moved. Everything just happened too fast. It was a horrible, horrible accident. By the time everyone figured out what had happened, it was too late to do anything."

Everyone involved believes that the entire tragic incident was caused by a series of mixups.

The silent alarm that first called police was tripped by three pool hall employes who had locked up, then gone back in to get something.

According to tests run by the state medical examiner's office, Bieganowski was under the influence of alcohol at the time of the incident.

Arriving at the scene, all the police knew was that three people were inside a closed and locked pool hall.

Saslaw, seeing Bieganowski approach Marquis, had no way of knowing who Bieganowski was or what he was doing. "I saw a guy stick a gun in the car of a friend of mine," he said. "I reacted. I didn't wait to ask questions."

Bieganowski, pushed by Saslaw, probably thought, everyone believes that Saslaw was another burglar, so he shot Marquis, who thought Saslaw had been shot, fired on his attacker.

"There was nothing Jerry wouldn't do for a policeman," Mrs. Curtis said yesterday. "He would've given them the shirt off his back or anything else they wanted. If only everyone also was. It's all so very, very bad."