Patrolman Albert M. Claggett IV had finished a monotonous eight-hour stretch standing watch at the emergency ward of Prince George's General Hospital. In two hours, the 26-year-old county policeman could head back to his wife and two young sons at their new home in Bowie. First, however, he had to close out his 10-hour shift by cruising the streets of "Section B" in Bladensburg.

It was 12:17 a.m. yesterday when Claggett said good-night to his relief man and the reception clerks and went out to his squad car. At the same hour, less than a mile away, two teenage brothers were leaving an apartment on 58th Avenue in Bladensburg and getting into an old brown Plymouth. They, too, would cruise the local streets.

These were the opening moments of a dark morning that would end with Claggett returning, fatally wounded, to that same emergency room, a fellow officer, 25-year-old James Brian Swart, lying dead on the floor of the prisoner processing room at the Hyattsville station, and the younger of the two brothers, 15-year-old Terrance Johnson, being charged with both slayings.

According to police investigators, Claggett and Swart were killed after Johnson allegedly ripped Claggett's gun from his holster at 2:40 a.m. as the youth was being fingerprinted in the basement of the Hyattsville station. The Johnson brothers had been picked up because their car fit the description of one that was seen leaving the site of a Riverdale larceny.

As soon as Johnson stole Claggett's gun, according to police the youth shot him once in the chest, fired two errant shots toward a nearby detaining cell where his brother, Melvin Johnson, was sitting, then encountered Swart and another officer who had rushed in from the outside hallway when they heard the shots.

As the two officers approached him. Johnson allegedly fired three shots, one of which struck Swart in the stomach. Swart was able to drag himself 10 yards down the hallway before he collapsed.

The six bullets in the 38-caliber revolver were by now expended, police said, and the suspect ran out of the processing room and turned down another hallway where five or six civilians were standing. There, according to police, Johnson walked unknowingly into the path of Cpl. Paul Low, who punched the youth with his fist and disarmed him.

Johnson, a ninth-grade student at Bladensburg Junior High School, was taken to the county jail at Upper Marlboro and charged with two counts of murder. Melvin Johnson, 18, a recent graduate of Bladensburg Senior High, was charged with driving a car with expired license plates and with being a vogahond.

The shootings of Claggett and Swart - the ninth and 10th country officers ever killed in the line of duty - come at a time when various segments of the Prince George's community are sharply divided over the performance of the largely white county police force.

The black community has been shaken by two recent fatal shootings of black suspects by white officers. The rank-and-file officers, meanwhile, have expressed growing concern over what they see as a lack of support - both morally and financial - on the part of Chief John W. Rhoads and the administration of County Executive Winfield M. Kelly Jr.

Many of the two dead officers' colleagues, while numbed and angered by the tragedy, noted that this time it was a young black man who allegedly killed two white policemen.

Laney Hester, president of the county's Fraternal Order of Police, put it this way: "It's interesting that with all the talk about white cops going around shooting innocent blacks that a couple of white cops get killed by a black kid. It shows that it can happen both ways - that there is a need for the police to protect themselves."

The family and friends of Terrance and Melvin Johnson appeared as shaken as anyone by the tragedy. One 16-year-old boy who lived next door to Terrance Johnson at 4241 58th Ave. was so upset when he heard a television report of the shooting that he slammed his fist through a glass door, nearly cutting it off at the wrist.

"The guy was shaking real bad," said another neighbor, Leroy Campbell. "He couldn't control himself. It was hard for any of us to. Terry was a good kid, he seemed to have everything going for him. I'm his best friend, and I can't believe it."

Terrance Johnson lived with his mother in Bladensburg, while the older brother, Melvin, lived with the father, Robert M. Johnson, in Palmer Park. The Johnson parents were divorced five years ago, according to Robert Johnson.

"I know the police around here," said Campbell. "They always give us trouble. Even when we're not doing anything but walking down the street. Terry didn't like them. But something bad must have happened in that police station to make him do something like that."

"He's smart and he knows how to handle things," said Johnson's sister, Pam, 19. "But he doesn't like to be taken adavantage of. That would get him upset if he thought he was being treated wrong. He might get agitated. If he did this, he did it because he panicked. Something had to scare him."

Michael P. Nemchick, the principal of Bladensburg Junior High, said Johnson had what he called "a violent streak." Said Nemchick: "He could get off very fast. He would be calm, all of a sudden get very angry, then be calm again."

Nemchick said that, according to his records, Johnson had always been a fairly good student, never in danger of being left back, but had experienced some behavioral problems, especially during the final quarter of the last school year.

"You can see a noticeable drop in his grades the last quarter, he failed three courses," Nemchick said. "He definitely took a turn for the worse once wrestling season was over (Johnson lettered on the school wrestling team). He was hanging out with a bad crowd, loitering around school."

Nemchick said that in May Johnson had to be subdued by two assistant principals after an incident in the school cafeteria.

"He got into an argument with a cashier over a meal ticket," remembered assistant principal, Roy Burley. "I came in and suggested we go in the hall and straighten it out. When I picked up the tray to hand it back to the cashier in the meantime, he went crazy, started swinging and all. I barely got him out of there.

"He kept struggling, trying to hit me until after we got into the hall. Then when he calmed down he was fine, even remorseful. He said he was sorry and hadn't meant to give anyone any trouble."

"As long as he felt his side was being heard and you listened to him he was okay," Nemchick added. "But if you tried to exert your authority you were in trouble. If he thought he was being crossed, you would have problems with him."

One of Chief Rhoads' top aides, Capt. Edward Armstrong, said the county police administration was now unhappily forced to second-guess itself about the shootings. "Whenever something like this happens, you have to look at the procedures you're using," said Armstrong. "They're going to be questioned automatically. You try to figure out what went wrong, how we could have prevented it."

Yesterday morning, at the Hyattsville station where the shootings occurred, several patrolmen on duty were more specific about what might have been done to prevent the shootings. One officer said that Claggett "made a mistake" by taking his gun into the processing room with him.

"When I go in there, I leave my gun with the clerk," said this officer. "Or, if I'm with someone threatening, I make sure there's another policeman in there with me. Claggett was alone in there. I guess he wasn't afraid of the kid."

Another officer said the county administration was at fault for not renovating the basement processing room and making it more secure. "There are too many people who can just walk in and out of this place."

As this patrolman was speaking, three county maintenance men walked into the processing room, a bleak and dusty 12-foot by 20-foot cubbyhole, and began measuring the door.

"We've got orders to put in a stronger one," said one of the maintenance workers. "We were going to do this anyway."

"That," said one of the officers, "is a dollar short and a day late."

Out in the Northview Estates section of Bowie, where Claggett lived with his wife, Carolyn, and sons aged 2 and 3, one of the many officers who came to express condolences yesterday offered a similar thought.

"We can talk all we want about how to make things better," he said. "But that's not going to help two dead men."