Anyone who suspects that the eleventh-hour histrionics of "Perry Mason" are not quite what you'll find in the average criminal trial should tune in tonight's episode of "Frontline With Judy Woodruff" at 9 on Channel 26. It offers a rare glimpse "Inside the Jury Room," and it is there, not in the courtroom, that the real drama of criminal prosecutions often occurs.

In a case of gratifying simplicity, a 42-year-old convicted felon who has followed the rules of his probation for nine years one day decides to emulate the video vigilante in CBS' "The Equalizer," enrolls in a mail-order detective course and buys a gun.

While trying to imitate the cops at a Wisconsin courthouse, the defendant is asked to produce some identification. Inexplicably, he chooses to show the police the sales slip for his .22-caliber pistol. Upon request he goes to his home, retrieves the gun, boards a bus for the police station, presents himself and is promptly arrested.

The man's trial is extraordinary in its total absence of any revelations or surprises. The performances of both attorneys are competent if not inspiring, and the defendant appears to be bewildered by the entire proceeding.

His lawyer does not dispute that there was a violation of the letter of the law prohibiting felons from possessing guns. Yet he asks the jury to find the defendant not guilty simply because they have the power to do so. And the stage is set for seven men and five women to confront their willingness to effectively nullify the law.

Theresk,3 are no shocking moments during the jury's deliberations. Yet as the jurors' debate continues, the program is quietly intriguing and ultimately compelling in its reflection of group dynamics and the functioning of the judicial system.

"Frontline" does mention that the power of a jury to nullify a law that seems unjust is the same power that enables a racist jury to perpetuate bigotry. But it fails to explain how "Frontline" was able to get a TV camera into the normally sacrosanct jury room in the first place, and, more importantly, what impact its presence may have had on jury members. One can't help but wonder which statements were made for the benefit of the viewing audience and how many thoughts were never uttered because they would be,2

Perhaps most unsettling is the nagging feeling that not every viewer of "The Equalizer" who is prompted to go out and buy a gun will turn out to be as harmless as the defendant in this case.