David Rabe's "A Question of Mercy," based on Richard Selzer's essay about his experience with a withered, terminal AIDS patient who wants help killing himself, shows its characters valiantly (and not so valiantly) trying to do the right thing. Of course, doing the "right" thing here is virtually impossible, given the vagaries of human emotion and the forbidding specter of American law; Rabe has said that he believes the issue of assisted suicide is "not really resolvable." So the play is a story without villains in which nobody wins.

As in Peter Shaffer's "Equus," which preceded "A Question of Mercy" at the Olney Theatre Center, a doctor walks the audience through a troubling case. The semi-retired Robert Chapman (James Slaughter) dispassionately tells us how it all started with a phone call from a stranger. From there, James Kronzer's turntable set--the same white multi-door oval from "Equus," only with a rotating floor now--whirls us to Chapman's meeting with the stranger (Thomas, the dying man's lover), then to Chapman's meeting with the dying man himself, an emaciated Colombian named Anthony.

Anthony is a pitiable figure, and, as played by Jose Carrasquillo, it's all he can do to get a few sentences out. The disease has not only weakened Anthony, it humiliates him almost hourly. How can Chapman refuse to help?

Chapman agrees, by degrees, but never really feels right about it. Thomas feels even worse. The idea of helping his beloved partner die is profoundly perverse to Thomas, and he's afraid of legal prosecution if the authorities discover that Anthony's death wasn't merely suicide, but assisted suicide. Thomas's lines of dialogue are full of incomplete thoughts and sentence fragments; if the physically ravaged Anthony barely has the strength to speak, the emotionally ravaged Thomas can barely assemble his thoughts into speech. Christopher Lane plays the role with a surface calm that is an obvious struggle; Thomas labors to be supportive, but you sense that what he really wants to do is scream.

Despite their reservations, Chapman and Thomas try to do what Anthony wants (aided by Susanah, a mutual friend of the suffering couple's). The questions then become how to do it and how not to get caught. It's tempting to say that the play gets bogged down in the details of furtively plotting a wished-for death that the law would nonetheless view as murder. But the difficulty of managing these details--the ironic banality, even, of someone asking what movie Thomas and Susanah should go see while Anthony is killing himself--is part of the point. None of the characters is cut out to operate on the wrong side of the law, and the play does not spare us their awkwardness.

The combination of human indignity and debated law leads you to expect a righteous howl from the playwright, but it never comes. Rabe doggedly stays in the gray areas, and director Jim Petosa's cast finds strength in ambiguity. Only Carrasquillo's Anthony seems to know exactly what he wants, insisting in a gentle, boyish whine that no one wants to argue with.

Watching "A Question of Mercy" is not a passion-filled experience; the show feels like a dramatic essay with minor touches of poetry (a tone that Slaughter handles quite well as our clinical guide). The play is not as sensational as "Equus" in terms of its case history or its theatrics, but then its intent is not to depict a world where religious and philosophical guidance is being radically questioned. Instead, it shows everyone drifting unhappily toward one man's death, helpless and confused from beginning to end.

A Question of Mercy, by David Rabe. Directed by Jim Petosa. Lights, Daniel MacLean Wagner; costumes, Rosemary Pardee; sound, David McKeever. With Mitchell Hebert, Helen Hedman and Grady Weatherford. Through July 4 at the Olney Theatre Center for the Arts. Call 301-924-3400.

CAPTION: James Slaughter, standing, and Jose Carrasquillo at Olney Theatre.