L'il Bit (Deirdre Lovejoy), the heroine of Paula Vogel's "How I Learned to Drive" at Arena Stage, grew up in what she describes to the audience as a "cracker" family in Beltsville. Her divorced mother, Lucy (Sarah Marshall), is a vulgar good-time gal; her grandmother (Rhea Seehorn) is a sexual hysteric; her grandfather (Timmy Ray James) is a coarse, cheerful misogynist; her Aunt Mary (also Marshall) is prim and proper; and her Uncle Peck (Kurt Rhoads) is . . . very fond of her.

L'il Bit "develops" early, which makes her an object of derision at school. She regards her burgeoning breasts as "alien life forms. . . . They're just using me till they can propagate and take over the world!" At home, she keeps trying to get her mother and grandmother to explain sex to her, but they're not very helpful. "Orgasm!" Grandma snorts to Lucy. "That's just something you and Mary made up!"

Peck, an uncle by marriage ("an in-law," as he takes pains to point out, rather than a blood relation), is a quiet, mournful, complex man. A veteran of World War II's Pacific theater, he won't talk about his military service, but the audience can speculate that it may be one reason he's an alcoholic. Or perhaps there are other reasons. Peck is a mystery, and Vogel intends for him to remain one. Certainly he is for L'il Bit, who is the child object of his affections, his attention, his predation--and, as this scathingly honest script makes clear, his love.

This is "Lolita" from Lolita's viewpoint, without all the fancy language and romantic agony. Fatherless, confused and lonely, L'il Bit enters into her liaison with Peck half-willingly. Finally, after seven years, she escapes to college. She's free of Peck but has become an alcoholic herself, and never makes it through school.

One of the things we never learn about L'il Bit--and this may be deliberate, but it also leaves the play feeling incomplete--is whether she ever achieved a satisfying sexual life. The one encounter we hear about is a matter of power and ego as much as lust, and she tells us that, when Peck first fondled her, "my body died," and from then on she lived in her head.

This omission is linked to another void in the play: the empty space where there should be anger. Not L'il Bit's anger at Peck; she has her revenge on him. But the anger that must have lain at the center of L'il Bit's awful family, which formed a conspiracy of blindness and silence about what was happening in front of them.

The shocking element in the play isn't the pedophilia or the quasi-incest; it's Vogel's refusal to pass judgment. There's no question as to Peck's responsibility--he goes after a child, not a teenager--and there's no question that he damages L'il Bit. But she won't deny that in his way he loved her, and that she loved him. It's this ambivalence that accounts for the play's penetrating, under-your-skin power. The audience is not allowed to settle into an easy moral position. We're forced to look the idea of forgiveness in the face and discover that, as with many nice-sounding concepts, it has aspects that are disturbing and terrible.

Molly Smith has directed with surreal verve, scooting the characters in and out of L'il Bit's memory. Somewhat unexpectedly, "How I Learned to Drive" is a wildly funny play, and Smith appreciates every bit of its strange humor. She gets sensitive, uncompromising performances from Lovejoy and Rhoads as the man and woman for whom moral horror and genuine affection are inextricably intertwined.

All the family except L'il Bit and Peck are played by three local actors--Marshall, Seehorn and James--and they're all terrific. Marshall's high moment is a speech she gives as Lucy on polite drinking--"A lady never gets sloppy"--then she turns around and gains our sympathy as the betrayed Mary. Seehorn is hilarious and unnerving as the grandmother and horribly vulnerable as the child L'il Bit, and James is entirely convincing as a series of nerds and hicks as well as a put-upon waiter.

American drama is full of plays in which the writers try to forgive their families. "Death of a Salesman," "The Glass Menagerie" and "Long Day's Journey Into Night" all come to mind. But in those dramas, though the playwright lets us know he's working overtime to be "fair," we're likely to end up appalled at the monsters he shows us.

Vogel doesn't indulge in this double-tracking. She won't make Peck a monster or try to insist that people who do things we despise are incapable of love.

How I Learned to Drive, by Paula Vogel. Directed by Molly Smith. Set, Kate Edmunds; costumes, Lydia Tanji; lighting, James F. Ingalls; sound, Mitchell Greenhill. At Arena Stage's Kreeger Theater through June 20. Call 202-488-3300.

CAPTION: Deirdre Lovejoy and Kurt Rhoads in the ambiguity-filled story of sexual abuse.

CAPTION: Deirdre Lovejoy's performance as a sexual abuse victim is affecting.