[Canby is a novelist, playwright, and film critic. Here, he offers a highly favorable assessment of The Cryptogram.]

The Cryptogram, David Mamet's spooky, very good new play, is elliptical but far less minimal than it initially looks. It's stuffed with the emotional bric-a-brac that leaves permanent scars on children, splits husbands from wives and rests lifelong friendships.

Under Mr. Mamet's direction The Cryptogram had its American premiere here on Wednesday night at the C. Walsh Theater. Though the American Repertory Theater's home is the Loeb Drama Center in Cambridge, it's presenting the play at the smaller theater in Boston, just behind the State House, as part of its New Stages '95 series. The Cryptogram, which has three characters and runs a scant 75 minutes without intermission, should be something of a coup for the group, which presented the first production of Mr. Mamet's Oleanna in 1992.

The new work doesn't have the topical kick of Oleanna, the temper-testing box-office hit about sexual harassment. Instead, it's a characteristically condensed Mamet consideration of matters that seem both more timeless and, in view of the playwright's stories about his own hair-raising childhood, more personal.

The Cryptogram takes place in a living room, which, as designed by John Lee Beatty, is a bleak commentary on every television sitcom set you have every seen. This living room, with the obligatory stairway at the back, looks as if it were in a permanent state of dismantlement, awaiting the movers. It contains one rump-sprung sofa and one easy chair with an ottoman. Nothing else, No lamps, no pictures on the walls. There aren't even any visible windows or doors.

Yet two floors above, there's an attic that, from what we hear, is stuffed with things hidden, stored, forgotten or abandoned: clothes, faded photographs, tackle boxes, old blankets. As various objects are retrieved from the attic during the play, it becomes evident that it not only is the repository of shared possessions but also functions as the collective unconscious of the characters. They are 10-year-old John (Shelton Dane), his mother, Donny (Felicity Huffman), and the family's best friend, Del (Ed Begley Jr.). Next to the boy, the most important figure in the piece is his father, Robert, who, having just abandoned his family, remains unseen.

Donny is a well-meaning but chilly woman who is furious when she learns her husband has departed, though not, it seems, totally surprised. Del, a feckless and aging librarian, a homosexual without any apparent social life of his own, has been Donny and Robert's pal since high school. He lives in a hotel room but, for lack of any impulse to do otherwise, hangs around their house. As things turn out, we learn that Robert has been using Del as casually as he has used Donny and the boy.

Young John is the play's focal point. He's an astonishing character. Not in any contemporary stage literature that I know has childhood been as movingly evoked as it is in The Cryptogram, John is certainly not an average child, but he's not necessarily some budding genius of a playwright. He's a particular child whose loneliness and prescience about doom give his mind a special alertness.

John is the kind of boy who's fascinated by the concept of thought. What are thoughts? Why do thoughts keep him awake? Do thoughts make real something that is dreaded? It isn't long before John is wondering aloud whether he's the dreamer or the dream.

He's the principal victim when Robert walks out on Donny. His mother is not a wicked woman, but she's so devastated by her abandonment that she hasn't the patience or the interest to deal with a precocious child. "I love you," she tells the boy at one point, "but I can't like you." She comes to see Del as Robert's partner in disloyalty, which is to give the poor fellow more credit than he deserves.

The Cryptogram is full of wit, though it's not exactly a barrel of laughs. At the beginning of the performance I attended, the audience was inclined to laugh easily, as if to announce its recognition of the playwright's idiosyncratic locutions. Indeed, those locutions seem so pronounced at the beginning that they border on self-parody. As the performance continued, however, that sort of laughter vanished. The script didn't become better (it's all of a piece), but the intensity of the performances made its sorrowful intentions clear.

It's not easy even for adult actors to play Mamet. As his own director, the playwright has done a remarkable job integrating young Mr. Dane's performance with those of the boy's far more experienced colleagues. Ms. Huffman, Mr. Begley and Mr. Dane are a splendid ensemble.

When you laugh in the course of The Cryptogram, it's less often because the lines are comic than because of the pleasurable skill with which the actors handle them. The dialogue tracks like a ball in an especially eccentric pinball machine. Speeches bounce off one another in totally unexpected directions, seemingly at random, for effects that prompt shudders even as they satisfy.

The Cryptogram is first-rate.