Messing up a classic

At a time when the arts are generally playing it safe, one must take one's scandals as they come. The one perpetrated by Sweden's Cullberg Ballet won't go down in history, but it will give people plenty to gossip about for a while. (The troupe made its North America debut at the Brooklyn Academy of Music here, and will appear in Minneapolis Nov. 20, Toronto Nov. 23-27, and Ottawa Nov. 29- 30.)

Remember the beloved Romantic ballet called ''Giselle,'' about a charming village maiden who falls in love with a count disguised as a peasant? Well, forget all that; and forget, too, the rhapsodic second act, which takes place in the mysterious domain of the ghostly Wilis. This new ''Giselle,'' by Mats Ek, is about a village screwball who galumphs around the green in a beret, pullover sweater, and bare feet. She could be the Annie Hall of the ballet world.

Act II is in a mental institution instead of at the graveyard of the Wilis. About the only likeness between the old and new ''Giselle'' is that the women are dressed in white.

The so-called ''white'' act of 19th-century ballet is a powerful theatrical convention. It always takes place in a surreal landscape, a place of whiteness. A release from reality, it allowed the choreographer his fullest expression of dance imagery. It was a gift from the librettist to the choreographer.

It is around this transcendent white act that this revisionist ''Giselle'' stops being a conversation piece and becomes a common failure. For whatever clever ideas Mats Ek has about plot have been lost on the level of choreography. Once one recovers from seeing the original ghosts reinterpreted as mental patients, there's nothing to see. In a way, the Romantic contrivance of the white act has the final revenge on a choreographer who's been scorning Romanticism. It shows him up as an emperor without clothes.

Oddly enough, it's in this supposedly pure-dance act that the dancer playing Giselle makes her greatest impact. Her name is Ana Laguna, and she's one of the most thrilling dramatic dancers I've ever seen. 'Soweto'

Laguna is also stunning in Ek's ''Soweto - South Africa,'' a short work on a second program of three ballets. But she doesn't have to transcend the dance. A celebration of the revolutionary spirit opposing imperialism, the subject matter of ''Soweto'' is in perfect accord with Ek's choreographic temperament. The aggressive, tormented, language that is found in both ''Giselle'' and ''Soweto'' looks foolish in the former and exactly to the point in the latter.