THERE IS no ground sufficient to justify closing a criminal trial to the public. But Prince George's County Circuit Court Judge Audrey E. Melbourne came close to closing her courtroom to all observers -- including the press -- this week in the case of Robert Willie Young. Mr. Young is accused of murder in connection with drug trafficking. He is alleged to be a member of a notoriously violent and reckless drug ring that was involved in the shooting of a U.S. attorney here in 1978.

As a result of that shooting, the judge, understandably, has some fear for the participants in the case before her. And that fear prompted her to consider whether anyone not directly involved in the case -- the press, for instance -- should be allowed into the courtroom at all. The normal occasion for attempting to close a trial is a claim of conflict between the defendant's right to a fair trial and the public's right to know. But in this case the press is simply being swept up in the judge's desire to protect her courtroom from the threat of violence brought by spectators.

On July 30, the judge did close a preliminary hearing in the case to the public and the press. And earlier this week, as the trial began, she considered closing the jury selection. But on reconsideration, she opened the door. Now the case is being tried with all spectators, except for the press, excluded.

Judge Melbourne's clash with the press in this case could be described as concern for the safety of the people involved in the trial versus the right of the public to know what is going on in its courts. Theoretically, someone with evil intent could pose as a member of the press to gain access to the courtroom and do violence to a particpant in the trial. But a judge has wide powers to protect her court.

Public knowledge of what takes place in the courts is paramount, if the American justice system is to remain a credible force in our society. Access to that knowledge must be guarded dearly, even at some cost. Police and bailiffs can adequately preserve order in the courthouse. To begin closing trials awakens larger dangers than any lone gunman can pose.