THIRTY YEARS AGO, the Supreme Court said it had been "unable to find a single instance of a criminal trial conducted in camera on any federal, state, or municipal court during the history of this country," except for courts material and juvenile proceedings. Yesterday, the justices said, in a vote of 5 to 4, that any criminal trial can be conducted in secret whenever the defendant, the prosecutor and the judge want it that way.

The justices reached this startling conclusion by not only discounting the value of 200 years of history but also brushing aside one of the basic sentiments on which this country was founded: Distrust of secret trials, bred by the excesses of the Star Chamber and the Spanish Inquisition, was well-extablished in Anglo-American law long before the Constitution was written. But the 1979 justices decided that document's guarantee of a "public" trial is one that can be asserted only by a defendant.

The court did not in perfunctory acknowledgement to some of the merits traditionally associated with public trials - an opportunity for citizens to evaluate the administration of justice, a check on the willfulness of officials and a decrease in the likelihood of perjured testimony. But the public's interest in these, it said, can be adequately protected by the prosecutor and the judge. The prosecutor can object if a defendant wants a secret trial, and the judge can refuse to grant one. This rosy view of the judicial system assumes that judges and prosecutors in every American community are above reproach, that the possibility of collusion between these officials and a defendant does not exist.

The problem that seems to have motivated the justices to sanction secret trials is the impact of prejudicial publicity on a fair trial. Secret proceedings, no doubt, can reduce the possible prejudice simply by reducing the publicity. But surely there are other, less drastic ways to deal with that problem.

It is of little solace that Justice Lewis F. Powell tried to soften his vote with the slim majority by saying the courts will protect the public against abuses of this new right to a secret trail. The holding of the court is clear. The public, and the news media, have no constitutional right to complain when a court's doors are closed. The Supreme Court has forgotten the wise words of Lord Acton: "Everything secret degenerates, event the administration of justice."