Ousmane Sembene's "Xala," first shown at the 1975 Cannes Festival and previewed last year by the Black Film Institute, has begun a regular commercial engagement at the K-B Studio 1, which may become an outpost for somewhat out-of-the-way imports.

Sembene, a 54-year-old Senegalese, turned to filmmaking in the early '60s after making his reputation as a novelist. He is the first American writer-director to achieve international recognition and "Xala" (the pronunciation is "hala," with a hacking sound on the "h), a satire on the social pretensions and insecurities of the new black ruling class in former colonial countries, is his fourth feature.

Adapted by Sembene from one of his own novels, the film benefits from an amusing premise and a reassuringly professional appearance. El Hadji Beye, a prosperous importer, enjoys membership in the Chamber of Commerce, his country's inner-most circle of influential businessmen, and cronyism with the president himself. Beye desires to put the icing on the cake by taking a third wife, a demure cutie no doubt younger than his eldest daughter, a severely disapproving coed who would prefer it if her mother, the stocial Madame Beye No. 1, took the event as provocation for divorce.

Everything is looking rosy for Beye until the wedding night arrives. Inexplicably, he finds himself unable to consummate the marriage. Fearing that he may have been victimized by "xala," the curse of impotence, he scurries around seeking remedies. His confidence is restored by a marabout, a Muslim holy man, but by that time Beye's new bride is feeling indisposed and his business indiscretions - he is revealed to have a weakness for writing bad checks - have begun to catch up with him.

One gathers that Beye's untimely attack of impotence is Sembene's way of putting a curse on his own country's most complacent or corruptible plutocrats. The film begins with a sequence of the president and his pals ostentatiously throwing out a three-member white Chamber of Commerce. In the next sequence two of the whites seem to have been kept on as flunkeys for the new regime, and they pass around attache cases filled with currency, which become Sembene's primary symbol of the sham independence of the "liberated" society.

Initially, there's something refreshing and exotic about witnessing this sort of ridicule emerge from a black African filmmaker in his own setting, and the movie is full of astutely observed evidence of the cultural contradictions in a modern African republic. The vistas of Dakar itself suggest the problems, with its cosmopolitan, European-style buildings, customs, costumes and values superimposed on African and Moslem traditions.

The major problem with the film is that the exposition is not nearly as clever as the premise. After warming to the idea behind the movie, one tends to cool off as it trudges toward a resolution.

Accustomed to a perkier rhythm, American audiences may find Sembene's slow tempo the most difficult aspect of "xala" to assimilate. I don't know if it came naturally or if it's a hangover from being trained in the Soviet movie industry, but it does make Sembene's style a bit of a chore. Several of the performers also slip into stilted postures or readings that lead one to believe Sembene may have difficulty putting less confident or experienced players at ease. There seems to be a vast gulf between the cast members who bring total self-assurance to their roles, especially Younouss Seye as the robust, strong-willed Madame Beye No. 2, and those who bring little or none at all.

Considering the amount of moral-ideological abuse heaped on him in the closing sequences, Thierno Leye seems a feeble choice as the unfortunate, overreaching Beye. His slight, slumped physique and rather squashed visage are effective in the early stages, because they accentuate the presumption behind his self-aggrandizement. One thins of him as the littlest of would-be big shots. Obviously, the best thing that could happen to him would be shamefaced return to his sensible older wives.

Sembene elects to subject him to a vindictive comeuppance in which he is spat upon by a group of beggars he had mistreated earlier in the story. The gesture seems way out of proportion; it's as if Beye had been envisioned as the most dangerous man in the country instead of the absurd, banal opportunist we'd been watching all along. It appears that the movie should end several scenes earlier, when Beye's business is confiscated and the indignant marabout returns to slap the curse back on him. It seems Beye passed him a bad check, too.

I'm sure that in certain enlightened business circles here the one unforgivable sin is trying to stick your guru with a bum check.