NEW YORK (AP) _ In ''Raw Youth,'' playwright Neal Bell takes an unsavory situation - the sexual entrapment of a U.S. congressman - and uses it as the unlikely framework for an unsatisfactory domestic drama about a father and son.

The father, Mel, is a small-time hood, out of jail on the condition that he help federal authorities snare homosexual congressmen. The bait he plans to use is his son, Sam, a one-time policeman who is gay.

Despite a first-rate production and three strong performances, the play, which opened Tuesday at off-Broadway's Playwrights Horizons, falters because the decision which sets the play in motion - the son's agreement to go along with the scam - is never entirely convincing. His consent makes the Abscam- like entrapment and its preparations seem more like an unbelievable theatrical device to bring father and son together than an opportunity for genuine plot or character development.

Their pigeon in these sordid goings-on is a married congressman from an unidentified Northeastern state. Despite his vulnerable situation, this government official is the least interesting of the play's three characters. The congressman is self-centered and unfeeling. His encounter with Sam, videotaped from behind a mirror at a sleazy Coney Island hotel, is handled discreetly.

Most of the play concerns Sam and his relationship with his father. The two men argue over Sam's sexuality; Sam's mother, who died of an unnamed illness; and the father's absence while his son was growing up.

Ben Siegler turns in a remarkable portrait as Sam who agonizes over whether to go along with his father. So does John Seitz as the father who must con his son and the audience. They are given strong support by James Ray as Gary, the hypocritical congressman who has been a persistent opponent of gay rights legislation.

Bell could have cut the play, especially an overlong second act. Director Amy Saltz pushes the action as hard as she can, although the endless arguments stymie her efforts.

The lighting by Ann G. Wrightson and Thomas Lynch's spartan settings are fine, especially Lynch's evocative hotel rooftop complete with a red neon sign.

Accepting Sam's willingness to participate in the plan in order to get closer to his father is crucial to the play. If the audience doesn't accept that idea, ''Raw Youth'' remains nothing more than a sordid little scheme.