More than two decades ago, playwright William Gibson endowed Broadway with one of its most affirmative dramas in the form of "The Miracle Worker." It was an extraordinary account of the young Helen Keller, little better than a beast, and the teacher, Annie Sullivan, who wrenched her, kicking and screaming, into the world of words. The climax of that saga -- Helen at the back-yard pump, realizing that water has a name, the very name Annie was finger-spelling in the palm of her hand -- remains a rare, exhilarating moment of the American theater.

In his newest drama, "Monday After the Miracle," which opened last night at the Eisenhower Theater, Gibson returns to those remarkable creatures. But 20 years have passed. The exhilaration of the breakthrough has given way to hard, exhausting routine, as Helen works her way through Radcliffe under the tireless tutelage of Annie. The trouble with miracles, Gibson suggests, is that you have to live with them -- day after day.

Because his female characters are intrinsically commanding, "Monday After the Miracle" is often a commanding play. Gibson handles several years' worth of events with a goodly amount of grace that helps attenuate the episodic nature of his story. And the earlier portions of the play, especially, are replete with moments that bring an audience to a hush. At this point of its pre-Broadway tryout, however, "Monday After the Miracle" is still grasping for that last-act punch. For two acts, it steadily noses its way into the souls of its characters. But the flood of pain and courage it seems to promise never materializes in the third act.

"The Miracle Worker" was essentially a two-character play -- Annie and Helen locked into a battle royal against the forces of darkness. In "Monday," Jane Alexander lends her fierce conviction to the role of the teacher, while Karen Allen, an appealing mixture of sweetness and determination, is the pupil, who by now has learned to talk, albeit in somewhat flat tones, by imitating Annie's tongue and throat muscles. But "Monday" also introduces a third character -- John Macy (William Converse-Roberts), an aspiring author and brash socialist, who at the start of the play applies for the job of editing the magazine articles that go out regularly under Helen's name. Is there, Gibson is wondering, any room for him under this roof?

Annie and Helen are mutually dependent creatures, the chiseler and the chiseled, wedded by time and achievement. ("We rose together -- mutual levitation society," Annie cracks with characteristic irony at one point.) Taken by Annie's grit and her flashing spirit, however, Macy courts her, marries her and settles into the house, an increasingly outspoken rival for the energies that have always been lavished on Helen. The three acts chronicle an uneasy alliance under pressure -- Helen, frightened that she will ultimately be abandoned; Annie, torn by her conflicting roles as wife and mentor; John, wracked by feelings of uselessness and then wracked by drink, as he realizes his hunger for attention will go unappeased.

In short, Gibson has written -- and not without humor -- an odd variation of the age-honored triangle play. John, although he feels expendable for much of the time, is still very much the bantam in the henhouse and sex plays its disquieting role in the proceedings. In the play's most stunning scene, Helen awakens sexually to John's presence, as they sit before a late-night fire. The flirtation goes no further than a kiss and light petting, harmless under any other circumstances. But here it registers with troubling potency, as we realize that another door has swung open in the dark night of Helen's psyche.

It is, however, Annie's plight that appears to occupy Gibson most fully. Headstrong, sharp-witted, driven, she cannot divorce herself from her magnificent obsession -- instilling perfection in Helen. At the same time, she is a woman with womanly needs; a mother who yearns (fruitlessly, it turns out) for a child of her own; a lover, who responds impetuously to a caress on the thigh. Her inability to reconcile impulses great and humble, noble and profane, eventually destroys her marriage and provides "Monday After the Miracle" with its climax.

Except that it's not much of a climax, for a fairly simple reason. Helen and Annie constitute one of the unique, and uniquely compelling, pairings of history. John and Annie share less theatrical bonds. We may be sorry to see him go at the end, but as yet Gibson hasn't convinced us that his departure will leave all that much of a void in Annie's life. Annie has made a sacrifice, perhaps, but it's the lesser sacrifice. And lesser sacrifices do not lead to rousing last-act curtains.

Although Converse-Roberts is an actor of a certain cocky charm, John Macy is really the least colorful character on stage, a slightly inconsequential, unfocused collection of thwarted ambitions and tangled desires. Neither Converse-Roberts nor director Arthur Penn has been able to hoist him up to a level that would make him an equal force among three. Since Allen's wide-eyed presence is touching from her very first entrance, and Alexander plays Annie with a vitality that runs from the inspired to the sardonic, he is, in fact, eclipsed from the outset.

John Lee Beatty's sets -- heavy Victoriana, profiled against a shimmering collage of foliage -- are a bit cumbersome, and the five-member cast (there are two supporting characters, a doctor and a friend of John's, whose main function is to plant crucial exposition) doesn't negotiate them with much ease yet. But the real trouble occurs in the third act, and it's Gibson who's suddenly doing the stumbling.

"Where do I fit in here?" asks Macy, helpless rage mounting in his throat, as he shatters a liquor bottle on the edge of a desk. It's the very question we've been asking all along. Alas, the answer -- nowhere -- has already occurred to us. Too soon. Too easily.

MONDAY AFTER THE MIRACLE. By William Gibson. Directed by Arthur Penn. Sets, John Lee Beatty; costumes, Carol Oditz; lighting, F. Mitchell Dana; With Jane Alexander, Karen Allen, William Converse-Roberts, Joseph Warren, Matt McKenzie. At the Eisenhower Theater through Nov. 13