"Carny," opening today at the Old Town and Tenley Circle, suggests intriguing sinister possibilities, but no one in a position of authority knows quite how to capitalize on them.

The opening sequence draws one into a milieu that promises Something Ominous. Gary Busey, who contributes an impressive performance, is introduced as a carny performer named Frankie, applying livid grease paint to his face. Frankie's specialty is the "bozo" act. Disguised in clownface and baggy overalls, Frankie sits on a platform over a caged-in water tank and dares customers to knock him off with baseballs. To encourage trade, the bozo needles people -- shouting insults at young men while paying lewd compliments to their dates.

On the night the story begins, Frankie succeeds in alienating a girl (Jodie Foster as a restless smalltown waitress named Donna) from her antagonized escort. The raunchy glamor and excitement that presumably attract her are embodied in Busey's humorous, challenging presence and the authentic carnival setting itself. Unfortunately, Foster doesn't bring much in the way of reciprocating lust and intensity to the portrayal of Donna.

Although cast as a sensation-starved teen-age runaway, she seems incongruously prim and preppie. Donna is meant to function as an explosive source of erotic mischief within the carnival troupe. Her decision to stick around and consort with Frankie causes immediate tension with his crony and trailermate, Robbie Robertson as "Patch," the carny manager and troubleshooter.

The plot is awkwardly organized around the familiar premise of a romantic triangle: Donna disrupts both the trust and the claustrophobic quarters shared by Frankie and Patch. However, the potentially messy consequences of Frankie's discovery that Donna is also consorting with his best pal are subordinated to a late-blooming subplot, in which the show folks are obliged to outfox gangsters making outrageous bribery demands.

The material never does achieve dramatic coordination or resolution. Nevertheless, in a generous mood the seamy show-biz atmosphere may appear novel and compelling enough to justify patience with the shapeless, unfinished story.

When he came to Washington almost 10 years ago promoting his marvelous documentary feature "Derby," Robert Kaylor spoke of wanting to direct a movie about carnival types. "Carny" is the culmination. It's also his first dramatic feature, a fact that shows.

Thomas Baum's screenplay derives from a story by Kaylor, his wife Phoebe and co-star Robertson, the former lead guitarist of The Band, making his acting debut while doubling as producer. The role of Patch confirms the heavy-lidded, melancholy sexual magnetism Robertson projected in "The Last Waltz." However, he doesn't begin to suggest an expressive range, so his photogenic qualities have no particular bearing on the character of Patch.

Kaylor's work frequently seems as tentative as Robertson's. The wryly observant viewpoint that helped transform "Derby" into a deadpan classic of American social comedy won't suffice for material with the tawdry, violent undercurrents that make "Carny" fitfully promising.

The movie is most effective when the filmmakers turn up the erotic heat. It might have been astute to let the ingredients boil over. (The strongest sequence involves a threat of sexual victimization to the heroine that is made dreadfully convincing by John Lehne, cast as a mob thug with ugly designs on her.)

Like a good many recent movies with serious pretensions, "Carny" seems more convincing around the edges than at the center. For example, an excellent supporting cast is augmented by a number of authentic sideshow performers. The most imposing and curiously affecting specimen is 600-pound George Emerson as Harold the Fat Man, who is usually secluded in a small private trailer. There's a haunting little scene in which he's discovered briefly at liberty -- standing outside in a rainstorm, bathing his squat, obese form in the downpour.

The "freaks" regard the carnival as a rare opportunity to make an independent living, just as the original Elephant Man welcomed a career as a sideshow freak as a deliverance from the workhouse. If "Carny" can be trusted, the same attitude prevails almost a century later among those unlucky enough to be confronted with a choice of undesirable alternatives.