Terrence Johnson, the 15-year-old Bladensburg youth accused of fatally shooting two Prince George's County police officers last June, plans to testify that one of the policemen was beating him just before the shootings occurred, Johnson's defense attorney said yesterday.

The remarks by defense attorney R. Kenneth Mundy was the first clear indication that Johnson, who is charged with murder, will contend he acted in self-defense on the morning when officers Albert M. Claggett IV and James Brian Swart were shot to death in the Hyattsville police station.

Mundy cited Johnson's planned testimony to County Circuit Court Judge Jacob S. Levin during a pretrial hearing yesterday, arguing that the defense should have access to all police records concerning brutality complaints against Prince George's policemen.

Levin first denied Mundy's request. Then, after a series of sharp exchanges between Mundy and State's Attorney Arthur A. Marshall, the judge agreed to examine the request further before making a decision.

Specifically, Mundy requested investigative reports on the arrest Dec. 4, 1975, of Thomas William Peete.That arrest, which Claggett took part in, led to a grand jury investigation on charges of brutality made against Claggett and other officers included in the arrest.

"I have given considerable thought to this request and I'm going to deny that motion," Levin said, early in the hearing, adding, "Nothing you say will change my mind."

Mundy then argued that previous incidents in which the officers "had shown belligerence," would lend credence to Johnson's testimony.

"Terrence Johnson will testify that he was being beaten, just before the shootings, by Claggett," Mundy said. "He will also testify that he and officer Swart had an altercation, first verbal, then physical, earlier."

Marshall apparently was angered by Mundy's remarks, saying, "Your Honor it seems apparent that the defense intends to try the Prince George's County Police Department for the jurder of two police officers."

"I hope we're not going to get into saying 'the police department is on trial,' throughout this trial," Mundy responded. "It sounds nice for the state, but it just isn't true."

Levin, after listening to the give and take, and hearing Mundy cite precedents for his request in Maryland law, recanted his denial.

"I'm going to take the matter under consideration," Levin said finally. He said he would rule on the motion late this week or early next week. Johnson's trial is scheduled to start Jan. 29.