"My Gene" avoids few of the pitfalls of the one-woman show, but it has a not-so-secret weapon at its disposal: Colleen Dewhurst, an actress who lends majesty to all she touches.

In this case, Dewhurst is saddled with an indifferent text about Carlotta Monterey O'Neill, the third wife of playwright Eugene O'Neill. The script has been pieced together by O'Neill biographer Barbara Gelb, whose knowledge of her subject is incontestable, but whose sense of what makes for stage drama is considerably less developed. Dewhurst supplies the fire and the fury, but she's fighting against great odds.

Imported from the New York Shakespeare Festival for a four-week run in the Kennedy Center's Terrace Theater, "My Gene" presupposes a familiarity with O'Neill, his works and the tempestuous woman who in the latter part of his life served as his inspiration, keeper, typist, lover, mother and nemesis. Even so armed, the spectator will find that the script behaves rather like a Mexican jumping bean.

It takes place in 1968, 15 years after the death of O'Neill, in St. Luke's Hospital in New York. Carlotta is haunted by the past and possessed of a fierce need to vindicate herself -- especially for having authorized the publication and performance of "Long Day's Journey Into Night." O'Neill didn't want that painfully autobiographical play produced until 25 years after his death.

Carlotta waited barely three years. "Long Day's Journey," however, won O'Neill a posthumous Pulitzer Prize, his fourth, and was instrumental in rehabilitating his status as one of America's greatest dramatists. "I restored your reputation for you," she rages in self-defense, and she probably did. But she still can't banish the guilt.

Alternating between moments of folly and lucidity, rage and compassion, Dewhurst takes us on a zigzagging trip down memory lane. Sometimes she is talking to an invisible doctor, sometimes to Esteban, a stuffed rag-doll monkey she calls "our own little hairy ape." O'Neill himself even surges before her troubled eyes. ("Oh yes, he's here. He's always here.") Little by little, a picture of a love/hate relationship comes into focus.

Gelb's instincts, however, are primarily documentary. She wants to provide us with the facts, the events, a chronology. To Dewhurst falls the herculean task of finding an emotional thread through the welter of anecdote and outburst and transforming old wounds into present agonies. If the patchwork text does not make her job easy, she is never less than a commanding presence. And when "My Gene" gives her an extended passage to sink her teeth into, the performance blooms with a lustrous intensity.

Ironically, however, the best of those moments are not Gelb's. Woven into the evening are excerpts from some of O'Neill's own plays -- Mary Tyrone recollecting the first time she met the dashing matinee idol who would become her husband ("Long Day's Journey"); Josie Hogan offering the redemption and solace of love to a drunken James Tyrone Jr. ("A Moon for the Misbegotten"). Suddenly, the words come up to Dewhurst's elemental power, support the resonance of her grave voice and amplify the beauty of her broad face.

Dewhurst is no longer carrying the laborious script all by herself and filling in a subtext Gelb has failed to provide. The change in the show's dimensions is startling. It is, if you will, the difference between journalism, which wants to get the details right, and art, which looks for more enduring truths. At its best, "My Gene" tells us more about the nature of madness than it does about a particularly cursed marriage.

As her troubled spirits wander, Dewhurst moves from the grim hospital room to the outposts of William Barclay's set -- a weather-beaten wharf, a boulder, a beach chair on a strand. By turns she finds herself in Marblehead, Mass., Sea Island, Ga., New York City, Northern California -- the sundry locales of the O'Neills' peripatetic life and so many stations in her personal Calvary. Director Andre Ernotte guides her peregrinations fluidly, but they are apt to be confusing to the uninitiated nonetheless.

"My Gene" is not afflicted with the off-putting bathos that characterizes "Confessions of a Nightingale," the one-man show about Tennessee Williams currently playing at the New Playwrights' Theatre. But it is a similarly erratic effort. Only Dewhurst's magnetic presence keeps it from falling into a hundred little pieces.

My Gene, by Barbara Gelb. Directed by Andre Ernotte. Scenery, William Barclay; costumes, Muriel Stockdale; lighting, Phil Monat. With Colleen Dewhurst. At the Kennedy Center Terrace Theater through July 4.