The theater is illusion. But it also is reality for the actors who spend part of their lives on the stage.

David Mamet, one of the ablest of the new playwrights, has turned to the theater itself to explore the age-old question of illusion and reality. His two-character play, "A Life in the Theater," now playing at the Studio Theatre, is both witty and touching in depicting the relationship between an aging actor on the decline and a young colleague whose career is taking off.

Mamet's short play covers one year in the lives of Robert, the older actor, and John, the younger. We see them backstage, putting on makeup, taking body exercises, rehearsing lines, bickering over their roles, talking about the theater. At times, we have a backstage view as they perform before an audience.

This production affords a good opportunity to sample Mamet's playwriting skills and style. Russell Metheny's backstage set, with its stage door entrance, notice-strewn bulletin board and winding steps to the changing room, allows quick scene shifts. Diana Molinari, who is making her directing debut at Studio, has an eye for little touches that mirror Robert's decline and John's growing confidence.

Mamet has an ear for vernacular speech and uses cliche with telling effect. After a performance, John hazards that one of Robert's scenes may have been a trifle, well, "brittle." "Over brittle?" asks Robert, echoing the language of an actor -- or a critic.

Robert loves to expound on acting and "the beauty of the theater." But the common bond between the characters starts to fray as their careers go in different directions. We see the signs of Robert's decline: He reaches for glasses, checks telltale lines around the eyes as he applies makeup, and protects himself by asking John "to do less" in a scene between the two. It is the old story of the old order yielding to the new. The question is whether Robert will accept the change with grace and wisdom.

As Robert, Morris J. Chalick can be pompous, querulous and still affecting. "The mirror is your friend at least for a few years," he tells John. And: "You shouldn't mock me. It's too easy," he says at one point, revealing the vulnerability under his self-assured surface. Richard Hart catches John's young exuberance, his growing impatience with his older colleague's pronouncements, and yet a tentative understanding.

But the Studio production does not deliver a gut wrench of emotions in the final scene when Robert must deal with the problem of drawing a line between illusion and reality in his life. It is sad, even touching. But it just misses being profoundly so. Perhaps this is because Robert has not engaged our sympathy earlier with more of an emphasis on his vulnerability under the witty surface. Perhaps John should feel his colleague's pain a bit more in the final scene.

"A Life in the Theater" continues at the Studio through Aug. 17, Thursday through Sunday at 8 p.m. with a special matinee scheduled at 2 p.m. on Sunday, Aug. 17. The theater space is in a converted garage-like building at 1401 Church St. NW, and a fund drive is under way to raise money for airconditioning equipment.