Circuit Court Judge David L. Cahoon, robed in a herringbone sport coat and maroon tie, strolled into Courtroom 9 at the Montgomery County courthouse in Rockville last week for the opening of a trial to assess damages in a car accident. But instead of taking his customary place behind the bench, Cahoon sat down with eight other men and three women in the blue seats of the jury box.

He was the first trial judge in Maryland -- and one of the first in American legal history -- to be impaneled as a member of a jury.

"It's a little different when you're sitting down with your peers," said Cahoon, 59. "Jury duty is somewhat similar to what judges do all the time. But it's easier to be autocratic when you're all alone."

By serving on the jury, Cahoon was actually answering his own summons. Since he is administrative judge of the court, his signature -- signed by computer -- is on every letter calling a new batch of jurors.

According to the American Bar Association, Cahoon's day-long stint as a juror Oct. 16, is precedent-setting, although a Virginia-based group called the Center for Jury Studies has recorded two occasions in which trial judges in Phoenix and Houston have been impaneled as jurors.

"As far as I know it's never happened before," said Wantland Sandel Jr., director of Judicial Administration for the American Bar Association in Chicago.

In 1976 the Bar Association adopted standards that would not excuse judges, lawyers or other professionals from jury duty. But judges whose names do get into the pool of prospective jurors are usually challenged by the lawyers involved in the case for fear that the judge-cum-juror might unduly sway the jury. "My God, on a point of law, who'd argue with a judge?" said Sandel.

Cahoon, who has been dispensing justice for nine years in the 6th Circuit, said the plaintiff, defendant and their lawyers knew his identity, but his fellow jurors did not. The two hours that the jury deliberated, unaware of the legal expertise in their midst, capped a long day in which Cahoon said he tried to remain incognito, going so far as to avoid people in the halls who might say "Hi, Judge."

Cahoon said he came away from the experience encouraged and enlightened by the quality of this side of the judicial process hitherto unknown to him.

"One of my strongest impressions was of the conscientiousness of the jurors," Cahoon said. "Everybody wanted to be fair, and consider all points of view."

The jury Cahoon served on was asked to assess the damages done to a woman whose neck was injured in an automobile accident two years ago. The other driver already had admitted being at fault.

Before the 24 prospective jurors, including Cahoon, were sent to Courtroom 9 to be questioned by the lawyers in the case, they were shown an orientation slideshow in the jury lounge, which featured, among other things, two pictures of Judge Cahoon.

"Nobody recognized me," Cahoon said.

The judge reported for jury duty by letter after his name was randomly chosen from voter registration lists. Actually it was the second letter. The first he ignored. "I was testing my own system to see if it was on the ball."

In court, before judge Robert Klapp, Cahoon expected to be eliminated by the lawyers arguing the case.

Defense lawyer John Powell asked Klapp to disqualify Cahoon, but didn't want to waste one of his four allotted challenges.

"Had it been a year ago, I would have struck [challenged] Cahoon," Powell said. "Credit the ABA with this. I went to a seminar on the philosophy of jury selection. I felt the judge would not be a detriment to our case."

The plaintiff's lawyer felt the same way. "When I saw him my first impression was to strike him," said Richard James. "Then I thought, why not give it a whirl, he's someone who's familiar with fair verdicts. A lot of the juries under Montgomery's one day-one trial system don't have a chance to become experienced jurors and the verdicts they give in civil cases are very low."

"I must say I was a little surprised when they didn't strike me," Cahoon said. He took a seat in the back row, and according to James, "was a very attentive juror." James admitted "it was a little strange" arguing to a jury with a judge in an otherwise normal line-up of housewives and government employes.

When they went to the jury room about 4 p.m. to deliberate, Cahoon said, he phrased his points as questions.

Two hours later, the jury trooped back into the courtroom and made an award of $11,500 to the plaintiff. It was only then that the other jurors learned Cahoon's identity.

"Any time you decide a case you are ain a very lonely position," said Cahoon. "It was very helpful to have other points of view."