PLAYWRIGHT Luigi Pirandello shattered the stage conventions of an era with his 1921 masterpiece, Six Characters in Search of an Author. He held up the magic mirror of theatre to theatre itself, thus reversing Shakespeare's dictum that "all the world's a stage." Pirandello's six characters broke down the barriers separating art from ordinary life and, in the process, exposed the inadequacies of both.

By placing Six Characters in the context of a rehearsal at the Loeb, the American Repertory Theatre ran the risk of exposing its own inadequacies. But Director Robert Brustein knows how to hedge his bets, and this wager paid off handsomely. The A.R.T.'s production is funny and moving, and gets to the heart of Pirandello's often elusive drama.

No curtain goes up at the beginning of this play. Lights remain on as the audience stumbles in and Assistant Stage Manager Tony Rudie sweeps the stage. Jack Phillips oversees the beginning of a Sganarelle rehearsal from a table littered with coke cans (the A.R.T. is actually in rehearsal for Sganarelle now, since they will be taking it to the Los Angeles Olympics next month). Actors drift in, warm up, and begin to rehearse.

Then Pirandello's characters appear. Dressed in black, swaying against a white background, they know how to make a dramatic entrance. They have interrupted the rehearsal in order to convince the A.R.T. actors to play out their story, a tragicomic family drama of incest, betrayal and death. Finally convinced that it would be more fun than rehearsing for Sganarelle, the A.R.T. actors oblige. But strange things begin to happen as the actors blur the distinction between reality and illusion. The characters' entire visitation has a sense of mystery, marvelously enhanced by staging, make-up, and numerous feats of technical wizarry.

WATCHING THE A.R.T. actors play themselves is, of course, amusing. They toss out references to Brother Blue and Brattle Street, to Harvard professors, Yale graduates, and to old mainstage productions. In true Pirandellian fashion, much of the action derives from improvisation. The dialogue is uneven--some jokes work, others fall flat. Occasionally the references seem designed to pander to A.R.T. subscribers, but on the whole, the company projects the sense of actors at work.

The Pirandello characters, too, must play themselves, but in a more metaphysical sense. Each allegorical character follows his own inexorable law, fixed in a reality which never changes. Actress Linda Lavin plays the Mother, a character trapped in an eternal moment of grief. Lavin, who played the title role in the CBS sit-com "Alice," makes her tragedy seem frighteningly real. Her limping movements, quavery voice and a face of pure sorrow bring her character to life.

Pirandello's characters stand on constantly shifting planes of reality. When the Stepdaughter (Lise Hilboldt) and the Father (Robert Stattel) see "real" actors imitating the gestures and words they had used in moments of true passion, they initially cannot recognize themselves. When they do, they greet the realization with both laughter and despair. Mirrors and lighting (designed by Michael Yeargan and Jennifer Tipton, respectively) make such scenes visually exciting and intellectually stimulating.

In 1967, literary critic George Neveaux wrote, "The entire theatre of an era came out of the womb of that play, Six Characters." Pirandello's revolution in form and content profoundly influenced the works of Sartre, Anouilh, Genet, Camus, Ionesco, Beckett, and many other playwrights. Pirandello's dramaturgy contributed significantly to this new form of theatre--his acceptance of the stage for what it was, his knowledge that it did not need to be a true-to-life copy of the real thing. He saw the stage as a place of magic and illusion.

Perhaps the greatest achievement of the A.R.T.'s adaptation is that it preserves the sense of the play as an illusion. Six Characters ends with a series of strange happenings and, though the audience knows they are only technical tricks. It leaves a feeling that something magical has occurred.