In retrospect, last night's performance by the Polish folk troupe Mazowsze, launching a week's visit at the Kennedy Center Opera House, was rather an anticlimax to the news that broke afterward of the defection in Canada of 11 of the company's dancers. Clearly, Poland's internal troubles don't stop at the country's borders.

There was, however, no indication of this new development either in the performances themselves or backstage last night. The company, one of the world's major folkloric dance and music ensembles, put on a splendidly colorful, rousing, zestful--and unruffled--show from start to finish. As popular entertainment, it had all the ingredients that make for audience seduction, including midstream singing of an American song--"She'll be comin' round the mountain when she comes"--which had the house joining in.

As an exposition of folk arts, it had its less than satisfying aspects. The streamlined packaging, calculated to appeal to spectators used to the razzle-dazzle of Broadway, almost overshadows the product, and in some ways removes the folk materials drastically from their original sources. A certain degree of theatricalization is a necessity in an opera house ambiance; one cannot directly transport peasant villagers onto such a stage and have them reproduce their native musical and choreographic arts without further ado. But the kinds of sugary harmonizations, slick orchestrations and bravura dance formations that dominate the Mazowsze program convert something that was once natural into something unmistakably commercial.

This said, it must certainly be noted that there was a great multiplicity of details to admire, from each of the remarkably beautiful, hand-crafted costumes to the smartly disciplined and vivacious singing and dancing. No less than 17 regions of Poland were represented, in dances that ranged from shepherds' gambols to wine harvest festivities, covering at the same time such characteristic musical and choreographic formats as the polka, the waltz, the polonaise, the mazurka and the oberek. On the whole, Mazowsze was least impressive where it looked much like every other folk troupe, and most beguiling where it was most distinctively Polish.