In the so-bad-they'r-good genre, certain movies stand out. "The Towering Inferno," "The Swarm," the King Kong remake - these are all unintentional comedy classics, and people who see them get their $3.50's worth in laughs if nothing else. Funny-bad films fill a real need, providing a dose of comic relief as well as a break from the usual ponderous movie fare of the '70s.

At first it seemed that "Ashanti," a slavetrading epic, would join this select group of groaners. The advertising campaign ("Only two men could rescue her . . . one driven by love, the other by revenge") sounded promising. And on the surface it seemed to meet all the criteria: marvelously miscast big-name actors, exotic locations, a cliche-ridden script, cue-card deliveries.

But "Ashanti" goes beyond funny-bad to just plain bad . Missing is that underlying humor, that sense of the actors' having fun with their roles, or at the very least the screenwriters' having fun with the script. No one here is having any fun at all, and with the absence of humor the faults quickly move from amusing to annoying.

It's all so predictable. As soon as you see Beverly Johnson heading off to the ocean for a picturesque skinny dip, you know it's only a matter of time before she's dragged away kicking and screaming. Supermodel Johnson, who looks like she's posing for a desert fashion layout in her lip gloss and strategically torn caftan, plays a United Nations doctor kidnaped by slavers while on duty in West Africa. Michael Caine, playing her distraught husband with all the emotion of a tree stump, spends the rest of the movie trying to find her. His performance is wretched in every way. If there's a film image more unlikely than that of Caine, all white and paunchy, jolting across the desert sidesaddle on a camel, it's hard to think what it is.

The movie's one upbeat note: Peter Ustinov's impersonation of an Arab slave trader. "What can I say, it's inflation, your highness, especially for virgins," he explains to Omar Sharif as they dicker over Johnson's price.

If the other big names had handled their roles with an equal amount of imagination, this might have been a good movie. But Rex Harrison, Omar Sharif and William Holden convey impatience and embarrassment more than anything else. Holden doesn't even attempt to act, probably feeling that no amount of skill could make up for the inanity of his lines. He's right.

ASHANTI - Beacon Mall 3, Capital Plaza, Centre, Crofton Cinema, Fair City Mall 3, Hampton Mall 2, K-B Rosslyn, Lincoln 2, Queen's Chapel Drive In, Rolling Valley 3, Roth's Featherstone, Roth's Quince Orchard, Roth's Seven Locks 2, State. CAPTION: Picture, MICHAEL CAINE HUNTS FOR HIS WIFE IN "ASHANTI."