Prosecutors yesterday raised the posibility that Steven Baines, on trial on a first-degree murder charge, may have known the Prince George's County police officer he is accused of fatally shooting.

Previously there was no suggestion that Baines, 27, and the officer, Antonio M Kelsey, 22, were acquainted. The defense argues that Baines shot the officer in self-defense, thinking he was a robber.

State's Attorney Arthur A Marshall told Circuit Court Judge Vincent J. Femia, with the jury absent, that Baines may have attended a roller-skating session with Kelsey. Both Kesley and Baines' sister, Stephanie Baines Young, belong to the Midnight Rollers Skating Club, Marshall said.

After the trial's fifth day ended, however, Marshall said the belief that Kelsey and Baines knew each other was based on an unconfirmed statement that they had skated together. The statement came from one propective witness who belonged to the club.

The prosecutor said he still had no evidence that Baines and Kelsey knew each other, even if they had attended the same skating session. Several members of the skating club may testify today. Marshall said.

Defense attorney R. Kenneth Mundy said Baines will deny that he ever knew Kelsey when he takes the stand, probably today, after the prosecution rests its case.

Baines is accused of shooting Kelsey twice in the head on Feb. 2 with the officer's own revolver outside Cox's liquor store at 7600 George Palmer Hwy. in Landover. If convicted, he could be sentenced to death.

Today, Marshall played for the jury a recording of the final radio communications between Kelsey and a dispatcher at the county police department's district headquarters in Seat Pleasant.

Kelsey was working off duty in plain clothes as a security guard at the store when Baines walked in. Inside the store, Marshall says, Baines displayed a bag of marijuana to Kelsey, prompting the officer to chase him outside and down the street.

Femia ordered the courtroom doors locked before the recording was played. The tape was switched on, and the courtroom grew hushed as the jury strained to understand the often unintelligible exchange.

The first transmission from Kelsey came at 8:45 p.m., according to a prosecution transcript that Mundy disputes. "Nine-ten," said Kelsey, giving his identification number, "send me a backup to Cox's. I've got a possible possession of narcotics."

"Are you around Cox's Liquors?" asked dispatcher Mark E. Brady. The answering transmission was unintelligible.

Less than a minute later, Kelsey's hurried voice was audible again: "He's running, I've got a number one (black) male, maroon coat, blue pants, possession of narcotics."

"Ten-four. Where are you running to?" the transcript continued.

Kelsey gave his location and then called "13," -- the police department's highest-priority distress signal.

Five seconds passed and Kelsey, according to the transcript, was heard from for the final time. ". . .the, ah, house on Columbia Park Road, a number one male with a beige . . . beige coat, plaid also involved . . ." According to Marshall, Kelsey was describing Charles Mayhew, a friend who had accompanied Baines to the liquor store. Charges were originally filed against Mayhew but later dropped.

A few minutes later, Kelsey was found sprawled on his back on a patch of grass, two bullet wounds in his head. He died a short time later in Prince George's General Hospital.

Two prosecution witnesses testified yesterday that Kelsey had been shot at close range. "The weapon was within six inches of the victim when it was fired," FBI special agent Evan Hodge said of one wound.