With police officers on rooftops filming demonstrators outside the courthouse and tight security inside, the painfully slow process of jury selection in the murder trial of Terrence G. Johnson began yesterday in Upper Marlboro.

Johnson, 16, is charged with shooting and killing two Prince George's County police officers June 26 in the Hyattsville police station while being questioned about a coin machine robbery.

Yesterday's session in Prince George's County Circuit Court marked the second start of the emotionally charged case, and in the sixweek interim the ranks of the black youth's supporters had thinned somewhat although anout 35 demonstrators did turn up at the courthouse.

But nothing was done to lessen the security precautions taken by the county sheriff's and police departments. Only the press, members of Johnson's family and close friends of the youth, and members of the families of the two slain officers, Albert M. Claggett IV and James Brian Swart, were allowed to watch as jury selection began yesterday.

In addition, sheriff's deputies set up a metal detector outside the door of Judge Jacob S. Levin's courtroom and screened everyone who entered.

This highly publicized case has split the community along racial lines. Jury selection is therefore considered an extremely delicate matter. As a result, 289 prospective jurors were on call yesterday.

All of them were marched into the courtroom, 15 at a time, to be asked a preliminary set of questions by Judge Levin. The start of the proceedings was delayed slightly when Johnson was 30 minutes late.

Once they did start, defense co-counsel Allen M. Lenchek immediately informed the judge that the defense had taken a countywide survey and found that 50 percent of those asked said they thought the defendant was guilty. Two-thirds of them, however, said they would tell the judge they could be impartial jurors if asked, Lenchek said.

"This is not an ordinary trial, your honor," Lenchek said. "Simply because of the nature of the offense it will be difficult to find an impartial jury and it is important that we be allowed the opportunity for extensive questioning of each individual juror."

"If you don't think your client can get a fair trial in this county why don't you ask that the trial be moved?" Levin asked.

"We think it will be difficult to select a jury anywhere in the state," Lenchek answered.

With that, the preliminary questioning began. Levin asked the jurors a brief set of questions: Have you heard about this case? What have you heard? Have you discussed it with anyone, expressed an opinion or had an opinion expressed to you? Do you have an opinion as to guilt or innocence now?

Anyone who said they had an opinion was immediately dismissed. Those who said they had no opinion were asked if they felt they could render a fair and impartial verdict.

By the end of the day 105 of the 289 jurors questioned had been asked to return today; the rest had been dismissed. Among those dismissed without being questioned were the wife of a county police officer, an FBI agent, a retired CIA agent, a retired D.C. policeman, two civilian employes of the police department and the mother of one of Johnson's friends.

Another 100 prospective jurors will be brought in for preliminary questioning today. After that the judge, State's Attorney Arthur A. Marshall Jr., and chief defense attorney R. Kenneth Mundy will question in detail those who survive the initial screening.

The first day of the trial turned out to be a tedious one for all involved. Members of the Johnson family, with the exception of Terrence's father Melvin, home recovering from a hernia operation, aimlessly drifted in and out of the courtroom all day.

When the jury selection is completed -- possibly by tonight -- Levin will order the 12 jurors and two alternates sequestered for the remainder of the trial. CAPTION: Illustration 1, Defense and prosecution lawyers and other court figures group around presiding Judge Jacob S. Levin and prospective juror, partially obscured at left, on first day of Terrence Johnson murder trial. Chief defense attorney R. Kenneth Mundy is at top center, and chief prosecutor Arthur A. Marshall Jr. is at top right.

By Joan Andrew for The Washington Post; Illustration 2, Defendant Terrence Johnson listens during jury selection as his trial begins. By Joan Andrew for The Washington Post; Picture 1, Terrence Johnson, in white jacket, arrives at courthouse for start of murder trial. By Larry Morris -- The Washington Post