Every once in a while the Joffrey Ballet makes a little dance history by stepping out of its boundaries. About a decade ago this establishment company commissioned works from the fiercely experimental choreographer Twyla Tharp. The Joffrey won for itself some hit ballets, and Tharp's career took off.
Now Laura Dean, another postmodernist, and the Joffrey are in partnership, and again both parties are richer for the bargain. Dean's new ''Fire,'' her second dance for the Joffrey, promises to be the highlight of the Joffrey season (through Jan. 16 at the City Center here).
A lovely dance in itself, ''Fire'' is also notable for the way it shows an essentially underground and idiosyncratic choreographer adapting to the big time without losing her voice. In ''Fire,'' Dean stretches her vocabulary way beyond the dances she makes for her own small troupe. In making the coloration of her movements more theatrical, she makes them more accessible. Working with ballet dancers gives her the chance to use toe shoes and explore partnering. Indeed, ''Fire'' is the first Dean dance in which men and women actually dance together.
Yet for all its new additions, ''Fire'' is the same old Dean. Like her other dances, one watches ''Fire'' for its beautiful exposition of pattern, its subtle contrasts between tension and serenity, and most of all for the seamless way the dance moves from one idea to another.
''Fire'' begins as a group work evocative of Russian folk ritual and ends up as an exhibition piece for individuals. In retrospect, one can deduce that the moment of change is a grand-right-and-left figure, when the communal circle transforms into six isolated couples.
But as one is watching the dance, one only feels the sensation of travel and change. The means of change is tucked away in the folds of the dance; it almost defies analysis. The Dean magic is like the magic of the seasons. Great changes work invisibly, yet to dramatic effect.
Another unusual addition to the Joffrey Ballet is Antony Tudor's ''Offenbach in the Underworld.'' Tudor is famous for probing, although not pessimistic, examinations of human activity. But this dance, made in 1955, finds Tudor poking fun at cafe society. Instead of creating complex people, he goes to town with the stock characters of cafe-society ballets: the debutante, operetta star, penniless painter, man about town.
Froth is what's intended, and froth is what you get, although one must add that ''Offenbach in the Underworld'' has much more serious dancing than is usual in the genre. Nor is the carefree atmosphere free of the Tudoresque attitude. The can-can girls are definitely on the far side of floozy. The romantic couples are properly in love, but we also see their moments of boredom.
Being deliriously in love can be a humdrum business on stage. Yet the most novel aspect of ''Offenbach in the Underworld'' is finding Tudor there in the first place.