Ayn Rand's "Night of January 16th," the inaugural production of the Encore Players, is playing at the Marco Polo restaurant in Vienna. The play is a thriller, a canny and often funny one, which proceeds like a court case, complete with judge, prosecution and defense attorneys, and accused, witnesses and a jury.

Members of the audience were mustered to play the jury, which they did earnestly, and when confined at the evening's end, they returned in seconds with a snappy verdict.

One international tycoon, Bjorn Faulkner, is dead, and most of the play consists of the systematic examination of witnesses, thereby permitting each actor in the rather large (17-member) cast to have his turn.

That is the play's blessing for Encore. Its pitfall is that some actors may feel pressured to be interesting. Some, resisting that temptation, will remain real; others will topple into the grand canyon of dazzling and pointless effects. The division here between human and grotesque comes out about 50-50.

Bob Greenspan provides a simple and starchy Dr. Kirkland, the medical examiner. Next, the janitor's wife, Mrs. Schwartz, is played by Joan Susan Zeigler in an advanced state of over-characterization: What is not muddled by a thick and curious dialect is blurred in a continuous flurry of motion. Elliot Werner provides an appropriately suspicious and seedy private eye as Homer Van Fleet.

Steven Shaffer plays policeman Elmer Sweeney with charm and clarity, and is a definite bright spot in the proceedings. Meanwhile, Nicolette Stearns, as Nancy Lee Faulkner, the young widow of the dead tycoon, carries the standard for superficiality: Every delivery and gesture is hackneyed.

Karen Havener Handley as the deceased's housekeeper, Magda Swenson, fares better: Her Swedish dialect is strong but comprehensible, and she presents this puritan without over-clouding her.

Tom Antush as the father-in-law of the deceased, John Graham Whitfield, may be a little flat, but he manages correctly to hold onto a sense of dignity throughout and emerges from the proceedings modestly intact. Dora Olson as the handwriting expert, Jane Chandler, is largely inaudible.

Glen J. Barrett plays Faulkner's accountant, Sigurd Jungquist, as a strange little man indeed -- but, with all his quirks, Barrett keeps him believable. Barrett's performance would receive more appreciation if only it were the lone characterization at such an extreme.

Sam Shulman gives one of the evening's best performaces as gangster Larry Regan, an interesting and even touching fellow. Shulman is relaxed, warm and generous. Nothing, therefore, could have been more disappointing than when Shulman, called upon to laugh, produced a loud, porcine, snorting noise from the depths of the canyon, utterly out of keeping with the rest of his good work.

Jina Ames does nicely as Roberta Van Rensselaer, the widow of a certain Lefty O'Toole, though she too drifts to the edge of the precipice with a repeated gesture of primping her hair several times too many.

Angie Anderson is present gently throughout as the stenographer, Bill Hutchinson adds youth to the courtroom as the bailiff and Michael Codel gives stature to the evening with his reliable Judge Heath.

Christine Nolan, as the accused Karen Andre, is splendid: a woman of passion and pride, and enormous determination.

Andre's defense attorney, Abbie Emanuel, and, as district attorney Flint, Alexander Gorny, deserve the highest honors for a geat deal of hard work -- they must deal with each member of this cast -- and capturing the manner we have come to know as lawyerly.

Although the run of this show is sold out, it should be pointed out that this troupe is the only one in the Northern Virginia Theater Alliance currently functioning in a dinner theater setting. The audience, mellowed by food and wine, behaves differently to one coming only to see a play. As the lights went out, a gentleman cried out instantly, "Now cut that out, Betty!" eliciting a few guffaws from other guests, presumably equally infantile. Titters and vocal whoops greet blackouts, and any surprising or suggestive information presented onstage. Of course, the Marco Polo restaurant, graciously providing Encore with a working stage, and reportedly providing an excellent meal, is not responsible for the behavior of its patrons.

If this kind of crowd is your cup of tea, then this theater venue will suit you just fine.

Encore Players, "Night of January 16th," Marco Polo restaurant, Maple Avenue, Vienna, through Nov. 11. For information, call 620-4140.