If the producers of "Ashanti" had any serious intentions of exploiting the comtemporary slave trade as a premise for a chase thriller, those intentions don't survive the entrance of Peter Ustinov as the principal flesh merchant, a harried Arab named Suleiman. This piece of casting puts a permanently frivolous complexion on the exposition, which tends toward sluggishness anyway. The filmmakers can't even break the monotony of pursuing the supposedly elusive Ustinov across jungle and desert by interjecting the fleeting gruesome homicide.

Ustinov won an Oscar playing a Roman slave trader in "Spartacus." The role, the company and the quality of illusion were vastly superior on that occasion. His familiar cuddlesome presence plays havoc with the fact that Suleiman is a swine, destined to provoke the nominally scrupulous hero, Michael Caine, to cold-blooded murder. Ustinov's accent is also an obstacle to the willing suspension of disbelief: It recalls Peter Sellers doing his Indian impersonation.

Caine and his wife, a statuesque black American beauty (Beverly Johnson) proud of her Ashanti roots, are a medical team on assignment somewhere in central Africa for the United Nations. While foraging near a village the doctors are visiting, Ustinov's minions kidnap Johnson upon her return from a refreshing skinny-dip in the nearest lake.

It would probably make more sense if Ustinov released her or killed her upon discovering that she was no ordinary tribeswoman, but this being the movie it is, he shleps her all the way to the Red Sea to hustle a dissolute playboy impersonated by Omar Sharif.

The gummy mixture of kinkiness and clownishness in "Mandingo" must have recommended Richard Fleischer for the directing job on "Ashanti," which maintains the same distasteful consistency. On one hand, the idea of slavery is supposed to make the audience feel sickeningly distressed; at the same time the situation is jerked for imbecilic sex gags, as Ustinov allows his henchmen to enjoy this or that prisoner just to stop their infernal lustful nagging.

To be effective "Ashanti" would have to generate the kind of visceral fear and excitement that affected many partrons at "The French Connection" and "Midnight Express." But Caine's attempts ot rescue his wife never throb with urgency. Considering the exquisitely voluptuous angularity of Beverly Johnson, the hero should be inflamed with urgency.

The plot marks time while Caine, a man of peace, is forced to pretend that he can rescue his wife single-handed. Rex Harrison and William Holden do guest spots as helpful pros who fall by the wayside. Finally, Caine hooks up with a relentless Arab tracker played by Kabir Bedi who has an old score to settle with Suleiman. What with fresh comic relief in the form of Caine's introduction to camel riding, the pace doesn't exactly quicken. By the time Caine and Bedi achieve a preposterous rescue on Sharif's yacht, it's much too late to care whether the heroine will return safe and sound. "Ashanti" will have to pin its hopes on an audience willing to indulge ugly porn fantasies while the good guys are kept fiddling around.