Terrence G. Johnson, the 16-year-old Prince George's youth who killed two policemen last June, was acquitted yesterday of murder charges bu found guilty of two lesser offenses-manslaughter and illegal use of a handgun.

Johnson was found innocent of six of the eight charges against him-all by reason of insanity-and could serve as little as one year in jail.

When the jury of eight whites and four blacks announced its verdict at 11:05 a.m. after 18 1/2 hours of deliberation over three days, the families and friends of the slain officers, Albert M. Claggett iv and James Brian Swart, sobbed, and some of them had to be helped from the courtroom.

As he watched his son led off inhandcuffs by sheriff's deputies immediately after the verdict was announced, Robert M. Johnson said, "I guess in a way it's reief. It could have been worse. But Terry still has to go to jail and that's terrible.In a way, I guess we were sort of lucky."

Prosecutor Arthur A. Marshall Jr., who was crying as he left the courtroom after the verdict, said, "My real concern is the impact this will have on the community. The defendant has become a very minimal part of this case, and that shouldn't be. Apparently the jury Bought the idea that there was some kind of conspiracy in the police department, that the police department should be on trail . . .

"I thought it was a very strange verdict. It was obviously a compromise verdict. They finally got to the point where they had to come out of that room with something."

The jury had told Judge Jacob S. Levin on Friday night that it was deadlocked and could not reach a verdict. But yesterday it took the jurors only one hour to return to the courtroom with their unanimous decision.

All 12 jurors remained standing at their seats as the clerk turned to foreman William H. Burns and asked him if the jury had reached a verdict.

"Yes, we have," Burns replied.

The clerk read each count fo the indictment. "To the charge of murder in the first as to the victim Claggett, how say you"? she asked.

"Not guilty," Burns replied.

Claggett's mother, Blanche Claggett, cried out "Oh no!" and began weeping while other family members, grim-faced, comforted her.

The clerk asked Burns for the jury's verdict on the charge of second-degree murder (Claggett).

"Not guilty," Burns said, and another gasp came from the side of the courtroom where the officers' families and members of the police department were sitting.

The clerk asked Burns for the jury's verdict on the charge of voluntary manslaughter, still talking about Claggett.

"Guilty," Burns answered and the cries of "Oh my God!" came from the other side of the room where the defendant's family and supporters sat.

The clerk moved onto the second count, "illegal use of a handgun while committing a crime of violence."

"Guilty," said Burns. Johnson, seated between attorneys Joseph Gibson and Allen M. Lenchek, began crying quietly and buried his head in his arms on the table in fron of him.

"To the charge of murder in the first degree as to the victim Swart, how say you?" the clerk asked.

"Not guilty," said Burns. Almost before the words were out of his mouth, Swart family members began crying and his mother, Rita Swart, said "I can't believe it."

Murder in the second degree? the clerk asked, "Not guilty," Burns said. Voluntary manslaughter? "Not guilty," said Burns.

Involuntary manslaughter? "Not quilty by reason of insanity," Burns answered.

Cpl. Paul Low, the man who captured Johnson immediately after the youth shot the officers in the basement of the Hyattsville police station last June, jumped from his seat and ran from the courtroom crying, "No! no! no! no!"

Outside the courtroom Low punched a table, then the wall with his fist and arms.

Inside, the clerk went through the rest fo the counts related to Swart's shooting and Johnson's alleged escape attempt from the Hyattsville police station.

"Not guilty by reason of insanity," was Burns' answer to all of them.

Pandemonium broke out in the courtroom as the final "not guildy," was pronounced. As the jurors were polled, one by one, the mothers of the slain officers had to be assisted from the courtroom. One of Claggett's sisters said, "That's the end for this county."

Laney Hester, president fo the county police union, said, "If anyone threatens a police officer in any way or pulls a gun on them in this county they better be ready to meet their maker. "They just told these people (the officers' parents) that their sons lives aren't worht a 'f---."

As Johnson was led away to the county detention center-the judge had revoked his bond after the verdict-his eyes glistened but he was calm and under control as a retinue of deputies surrounded him. Sentencing was set for May 3.

"I'm disappointed," said defense attorney Lenchek. "We thought we had a lot of evidence to prove self-defense on Claggett."

"It was strange," he said, "But inconsistent verdicts are not all that unusual." Lenchek said he would file for a new trial on Monday and would also file a motion for the release of his client until sentencing.

While most of the Johnson supporters left the courthouse in Upper Marlboro and dispersed quickly, members of the Claggett and Swart families and police officers who are their friends gathered in Marshall's fourth floor office.

Caroline Claggett, who has refused to talk to all newspaper reporters since the shooting, told WJLA-TV-7, "We're just sitting here crying and trying to keep our cool.

"Rusty claggett loved his county and loved doing his job. He loved everything about it - the uniform, the badge. . . I just can't picture him being mean or cruel. He was kind and loving.

"I just don't know what's going to happen now. I don't see how anyone can put on a uniform and go out there without feeling like a target."

Claggett's mother said she dreaded returning home to Florida and breaking the news to her husband, former county police lieutant Albert M. (Buck) Claggett iii. "I don't know how I can tell him," she said simply.

While the families treid to comfort one another, Marshall sat in the reception area, sipping a drink from a paper cup, and said he would try the case the same way if he had it all to do over again.

"I just keep thinking some of them (the jurors) went into the courtroom with some opinions, a philosophical bias. My major concern is what this does to the administration of justice in this country, this state and in the nation.

"I think this will have a tremendous impact on the county police. If you can stand up and say that you can shoot and kill tow policemen, well, I just hope that doesn't mean that if a policeman stops a car someone can just shoot him and say, 'I'm black and young and he was talking mean to me.'"

Johnson is black and his defense had become a cause celebre in parts of the community during the last nine months as rallies, fund-raisers and marches were staged in his behalf.

Immediately after the shootings last June 26, members of the black community raised a cry of brutality, saying that Johnson was being beaten by Claggett and alleging that the beating of young blacks was standard operating procedure among members of the police force, which is 92.8 percent white.

Members of the police department insisted that police brutality and race had nothing to do with the shootings. They claimed that Johnson had been a troublesome prisoner and had given both Swart and Claggett a hard time before Claggett took him into the tiny fingerprinting room where Johnson stole his gun.

Those conflicting claims were the crux of the lawyers' claims during the trial, the prosecution describing Johnson as an arrogant, cold-blooded murderer, the defense depicting him as a frightened youth, scared out of his mind, acting in self-defense.

Johnson took the stand in his won defense during the 11-day trial and testified that he had not given the officers a hard time and believed he was going to die when Claggett took him into the fingerprinting room.

He had been arrested along with his brother on suspicion of breaking into a laundromat coin box.

He testified that he was kicked in the groin by Swart in the processing room and when he swung a chair at Swart he was taken down in the corner of the room by Swart, Claggett and a third officer.

During cross-examination Marshall tried for 90 minutes, using "every trick in the book" by his own description to get Johnson to change his story.

But even though he broke down and cried at one point, the youth failed to crack. Marshall later asserted that Johnson had shot the officers "because he was trying to show his brother how tought he was."

One key prosecution witness, Officer Steven H. Roberts, testified that Johnson looked "cool, calm and collected" when he fired the shot that killed Swart. Roberts was standing next to Swart when he died.

Johnson's brother Melvin, 19, who took his younger brother for a ride on the morning of the tragedy, also took the stand to tell a strange tale of the events-which he witnessed from a nearby holding cell-that contradicted all other testimony, including his brother's.

Melvin Johnson was not in the courtroom when the verdict was announced becuase Judge Levin had banned him after he reportedly laughed in the face of Claggett's mother Friday night after the dead-lock was announced.

Johnson could be sentenced to a maximum of 10 years in prison on the manslaughter conviction and a maximum of 15 years on the handgun conviction. If he were to reveive two maximum sentences, he would be eligible for parole in five years. The mandatory minimum sentence he could receive is five years and he would be eligible for parole in one year.