In winding up a two-week engagement at the Kennedy Center - the company's first visit to his country - the Ballet Nacional de Cuba unveiled one final, remarkable surprise this past weekend.

For the Saturday afternoon performance of "Giselle" that found Loipa Araujo and Lazaro Carreno in the lead parts, the role of Hilarion, Giselle's rejected peasant lover, was assumed in a last-minute substitution by Antonio Gades. The previous week, in "Ad Libitum," his duet with Alicia Alonso, Gades had reminded us of that combination of soulful intensity and swimmering sensuality that had made his appearance here with his own flamenco troupe some years ago so memorably electrifying.

Saturday's "Giselle," however, was his first appearance ever in a classical ballet. Backstage that evening, he said he had done it as a gesture of gratitude to the Cuban troupe. Whatever his motivation, the result was the most extraordinary Hilarion in memory. His execution of the few dance steps the role requires admittedly sketchy, but the mimetic clarity and dramatic conviction he brought to the part made his performance a model of artful characterization. Unlike most Hilarions one sees, he emphasized not a spiteful, bruised ego, but adoration for Giselle and heartbreak over her collapse - he was so compelling one wondered why Giselle ever turned him down.

Gades, too, was responsible for the highpoint on the Latin side of the company's touring repertory. His "Blood Wedding" proved a magnificently spare, austere rendering of the Lorca tragedy, using the flamenco stance and steps as the base of a powerfully histrionic dance idiom.

Most impressively, the ballet - like flamenco dancing itself - makes constraint the measure of passion: the closer the approach of the mortal climax, the slower and more fiendishly controlled the movement becomes, as in the excruciating dagger duel between the male antagonists.

Otherwise, the interesting but decidely uneven Cuban part of the company's repertoire ranged from the appallingly meretricious "Carmen," through some virtuosic or humorous trifles, to such sporadically effective but ponderously allegorical works as "Oedipus," "The House of Bernarda Alba" and "Genesis," to the charming period imagery of Alberto Mendez' "Tarde en la Siesta."

Though her "Giselle" has lost its erstwhile fluency and radiance, Alonso remains, in such classics as "White Swan" and "Pas de Quatre," and in such contemporary pieces as "Oedipus" and "Carmen," the reigning artistic and technical model for the company.

Alonso, though, can keep the classic, folkloric and ethnic strands of her dancing quite distinct, fusing them only where the context requires this. The company, is less successful in this respect. Their, theatrical aptitudes, precise mime and ensemble, marvelous leaps and extensions, and the male machismo quotient all serve them splendidly in the Cuban repertory. In the classics, too often heaviness, excess thrust and eccentric placement mar stylistic purity. In retrospect, the company seems an attractive, technically proficient, somewhat roughhewn group. In one regard, they are a paradigm for all the rest of the ballet world: 'This is the most integrated troupe we've seen, black and brown and white dancing side by side in all ranks and stations.