'THE Rapture" takes its title from a belief of many Christian fundamentalists: that shortly before the Apocalypse, true Christians will be taken from Earth directly into God's presence, thereby escaping the trials and torments of those left behind.Focusing on a "born-again" woman who fervently believes in such teachings, the movie is a flawed but ambitious effort to treat evangelical Christianity in dramatic terms. It's not a great film, by a long shot, but it's riveting to watch - if only because it deals with a part of American religion that rarely finds its way into mainstream cinema. Sharon, played by Mimi Rogers, begins the story as a sensual "swinging single" who indulges in small-scale orgies with her boyfriend and strangers they pick up around the city. Her life is as empty as it is lascivious, and she unconsciously longs for something to give it meaning and purpose. Picking up hints of a religious group she'd never heard of, she becomes curious to learn more, and gradually works toward a moment of decision; this comes at a time when she's plunged into despair, and it instantly transforms her. She changes her habits, marries a born-again man, and becomes a clean-living citizen with solid commitments to her family and her fundamentalist community. After an unexpected tragedy in her life, however, she begins to feel that God is calling her in a special way - to forsake all earthly things and take her daughter to the desert, there to be "raptured up" immediately. The last portion of the story shows her leaving the framework of her religious group and acting on her own notions of what God wants from her. The movie ends with the Apocalypse itself, complete with Four Horsemen and other Biblical imagery. By this point Sharon's harsh experiences have tau ght her to rely on her own conscience rather than dogmatic teachings, and the last scene finds her still wrestling with truly ultimate decisions. "The Rapture" was written and directed by Michael Tolkin, a Jewish author who decided to take fundamentalism as his theme because of its growing presence on the American landscape - so pervasive, he said during the recent New York Film Festival, that some 50 million Americans identify themselves as fundamentalists of some kind. He treats his Christian characters respectfully, appearing to take their beliefs and attitudes at face value during much of the story. This lends a ring of truth to the picture, a t least until the conclusion, which unfortunately makes little sense on any terms, be they grounded in faith or human reasoning. "The Rapture" is a minor film in many respects. It's often fascinating, however, if only because it deals with material usually exiled from movies, carrying some implications of its subject to (and considerably beyond) their logical conclusions. What's most impressive about "The Rapture" is not its cinematic quality or religious insight, but its willingness to take a serious fictional look at an aspect of contemporary religion that's hardly geared to easy marketing or box-office success. True, it isn't the only current film with religious leanings; just now there's also "Black Robe," a historical study, and "The Fisher King," which buries its religious inklings in cinematic foolery. Sight and Sound, the British film magazine, reports that "Fisher King" director Terry Gilliam sent a telegram to the Toronto Film Festival after receiving an award there, thanking it for justifying his "decision to sell out." Whatever its failings, one can't accuse "The Rapture" of selling out for a second. I t isn't always coherent, but its inquiries are unquestionably sincere. Rated R for sensuality, language, and violence.