In the art of the irish step-dancer, the feet are everything; the torso remains upright and unbending, the hands stay firmly down by the side, pointing to the earth, and even the knees usually stay close together except in an occasional high kick. But the feet, moving constantly in intricate, ever-changing patterns, kicking out to the side, weaving in front and back of one another, are a miracle of pure, abstract motion.

Last night in Georgetown's Gaston Hall, the feet of Mike Flatley, who may be the world's best step-dancer, were like the hands of Vladimir Horowitz in power and agility if not in musical nuance; they were working, after all, not on a piano keyboard but on a wooden stage whose high polish had to be tamed with several applications of Coca-Cola to preserve life and limb.

Flatley (a native of Chicago) was the most spectacular feature of a very spectacular evening of Irish music and dancing entitled "The Green Fields of America," which is currently touring American cities under the auspices of the National Endowment for the Arts. The eight-person ensemble included seven musicians and two dancers (Flatley also plays the flute).

All were excellent and two were outstanding: fiddler Liz Carroll and piper Bill Ochs, who played all too few solos on the uillean pipes, a gentle, melodic cousin of the larger, coarser and more familiar bagpipes.

The concert ran late, and when it ended the musicians and much of the audience retired to Kelly's, a natural habitat for this sort of activity and a place where the floor already has a coating of Coca-Cola-or something.