Cheryl Lynn Talbert, 24-year-old girlfriend of accused police slayer Steven Baines, testified for the prosecution yesterday that she saw Baines kneeling over the body of Officer Antonio M. Kelsey on a street in Landover last Feb. 2 and that he later said, "I think I shot him."

Talbert testified for more than four hours yesterday at the Prince George's County Circuit Court trial of Baines, 27, charged with first-degree murder in the slaying of Kelsey, who was off duty and working in plain clothes as a liquor store security guard when he was shot to death last winter.

If convicted, Baines could be sentenced to death.

Kelsey was found near Cox's Liquors in Landover fatally shot in the head with his own gun after chasing Baines down the street outside the store.

State's Attorney Arthur A. Marshall, prosecuting the case personally, argues that Kelsey pursued Baines from the store after spotting him with marijuana and that the defendant shot Kelsey knowing he was a police officer.

Defense attorney R. Kenneth Mundy maintains that Baines shot Kelsey in self defense, thinking he was a robber, not a policeman.

Talbert, testifying for the prosecution as a result of an agreement that a related murder charge against her would be dropped, told the jury she drove to the liquor store the night of Feb. 2 with Baines and three other passengers -- two of them young girls -- to pick up some liquor on the way to her mother's home. They smoked marijuana on the way, she testified.

Inside the store, Talbert testified, Baines and Kelsey -- who was sitting at the end of a counter -- began staring at one another.

When Kelsey followed them outside, Talbert testified, Baines told her to get in the car. He then became involved in an argument with the policeman in the parking lot.

Baines and one of the passengers, Charles L. Meyhew, 28, of Oxon Hill, finally ran down the street, and Kelsey followed.

Driving around to look for Baines, Talbert said, she came across two figures on the ground and pulled the car up, shining her headlights on them.

Suddenly, she said, she heard two shots and saw a flash. One man was kneeling over the second, getting up. She called "Steve" and opened the car door. Baines got in.

"I think I shot him," Talbert said Baines told her. As they drove on, she testified, Baines added, "I think I shot him in the head."

Talbert, a Seat Pleasant resident, had been charged with being an accessory to first-degree murder. Marshall agreed to drop the charge against Talbert if she testified for the prosecution.

During cross- examination, defense attorney Mundy suggested that Talbert had modified her account of what happened after Marshall and her attorney arranged what Munday called the "deal."

"You would have done anything to get out of jail, wouldn't you?" Mundy demanded.

"Yes," Talbert responded.

Mundy read Talbert portions of her Feb. 27 grand jury testimony and suggested that Marshall had led her to make statements against Baines. "You were willing to answer anything at that time, weren't you?" he asked.

"Yes," she replied.

After Baines got in the car, Talbert testified, she drove to her mother's house in Glen Arden, then to Baltimore before she and Baines returned to her apartment. The next morning, she said, they went out and bought a newspaper "to see if someone was shot dead."

She and Baines later turned themselves in.