Police officers testified yesterday they found a bag containing about $50 worth of marijuana near where a Prince George's County police officer was slain.

The testimony is a key element in the state's case against Steven Baines, 27, who is charged with first-degree murder in the Feb. 2 shooting of Antonio M. Kelsey, an off-duty officer who was killed after chasing a man prosecutors say he saw with the drug.

Officers yesterday told a county Circuit Court jury that they discovered a bag containing about 7/10 of an ounce of marijuana near where they found Kelsey shot in the head on Columbia Park Road in Landover.

Other witnesses have said that Baines ran behind a service station in an effort to escape Kelsey, who had chased him from a liquor store where Kelsey worked in plain clothes as a security guard Baines, who has pleaded innocent, contends he believed he was fleeing from a robber rather than a police officer.

States Attorney Arthur A. Marshall Jr. maintains that Kelsey gave chase after the defendant showed a bag of marijuana to the officer inside the store. Baines' girl friend, Cheryl Lynn Talbert, testified Wednesday that she and Baines smoked marijuana while they drove to the store, Cox's Liquors, 7600 George Palmer Hwy.

She also testified she saw her boyfriend kneeling over the officer's body and that he later said, "I think I shot him."

The woman's sister, 11-year-old Juanita Talbert, yesterday morning gave the court her version of what happened when she and her sister drove up to where Baines and Kelsey were wrestling on the grass after the chase.

The girl calmly told the jury that she watched Baines rise to his feet while Kelsey lay on his back, and then saw three "sparks".

Baines "jogged to the car," the girl testified and told Cheryl Talbert: "Oh baby, I told him to leave me alone" "Everything's going to be all right," Juanita said her sister responded.

As her sister had the day before, Juanita Talbert reenacted the shooting, using 21-year-old Allegro Kelsey to play the part of his slain older brother.

Defense Attorney R. Kenneth Mundy objected on Wednesday to Marshall's use of Kelsey and asked for declaration of mistrial.

Presiding Judge Vincent J. Femia rejected the request but ordered Marshall not to address Kelsey by name.

During cross-examination Mundy showed Juanita Talbert portions of a Feb. 8 statement she made to police, and pointed out an inconsistency, "Maybe some things I remembered then I don't remember now," she conceded.

A short time later, Femia recessed the trial and the girl walked outside the courtroom, where she broke into tears. When court resumed, she was excused after the judge gave her a standard warning: "You are not now to talk to anyone who is yet to testify."

"But I can talk?" she asked.

The trial will resume Monday morning, when Marshall will call the final prosecution witnesses.

Police recordings of Kelsey's final radio communication with his station will be played and the medical examiner who performed the autopsy will testify, Marshall said.