The pretext of "Christine," the latest horror movie derived from a Stephen King best seller, sounded even more gimmicky than usual: a kind of "My Demon Mother, The Car," in which a nebbishy teen-ager lovingly restores a beat-up Plymouth Fury, whose diabolical powers then possess the youth, body and soul. But it was difficult to imagine an inventive movie thriller from such material, especially under the direction of John Carpenter.

Now at area theaters, "Christine" does indeed suffer from the preposterous, low-octane nature of the devil-car pretext.

But this satanic nonsense is saved from strictly facetious appeal by a few sensational pictorial effects, notably the sights of Christine speeding after a victim while engulfed in flames or miraculously repairing her own battered body, and by the no-nonsense performances of an excellent cast, especially Keith Gordon as the obsessed and transformed Arnie Cunningham.

The most fundamental conflict is the emotional tug-of-war between Arnie, the wimpy, car-infatuated teen-age protagonist, and his domineering mother. Nevertheless, Carpenter and screenwriter Bill Phillips never quite pry open King's obvious can of psychological worms, which demands that Christine the Fury emerge as a diabolical rival to Mrs. Cunningham. Perhaps reluctant to show brainy, upper-middle-class Arnie using Christine as an avenging vehicle against parental authority, the filmmakers work off the kid's resentments rather indirectly: against safely scummy antagonists like the auto shop hoods who try to terrorize Arnie in class and later vandalize his prize possession.

Once rescued from the junk heap and reanimated by Arnie's devoted attentions, the jealous Christine is supposed to break up his romance with a class dreamboat, Leigh. But the erotic undercurrents in this supplementary triangle are muddied by oddly hesitant exploitation. To be specific, Leigh professes to find the car creepy just moments before it tries to strangle her--and surely this order of events is out of whack. Any fool can see that Leigh has no business anticipating Christine's aggression. The car should take spontaneous offense--at the indignity of being used as a necking haven by Arnie and Leigh--and try to eliminate any potential rival.

In his bullied phase, Arnie emerges as a more original, impassioned image of a high school wimp than you anticipate. Gordon keeps the characterization vivid and surprising throughout the metamorphosis into devil's schizo. Restoring Christine gives Arnie a new sense of self-esteem and sexual confidence, and Gordon shows the character shedding his weakling cocoon for a wolfish coolness and defiance. He begins to resemble Fonzie as he might be written and played by John Sayles.

The emboldened Arnie also demonstrates previously submerged aggressive, bullying tendencies, and when Arnie and Christine seem to blend identities, it's not a difficult illusion to accept: Gordon has gone persuasively, not to mention entertainingly, bonkers right before our eyes. Arnie is the sort of assignment that could easily turn an unwary or unskilled actor into a laughing stock, but Gordon is imaginative enough to capitalize on the cliche's that threaten to humiliate him.

There are also expert performances in less imposing roles by Robert Prosky as a gruff garage owner; Roberts Blossom as a devious old coot; Christine Belford as Mrs. Cunningham; Alexandra Paul as Leigh; and John Stockwell as Arnie's protective and then alarmed best friend Denny, a straight-arrow athletic hero felled by a near-crippling injury under Christine's influence.

In fact, Carpenter seems so comfortable with the cast that one suspects it wouldn't hurt him to take a vacation from the horror genre, which he has always tended to stylize more portentously than necessary. "Christine" won't be mistaken for the best movie of the holiday season, but between the smartest effects and Gordon's canny performance, it's more diverting than the material probably deserves.