The form is old and set, but its appeal remains fresh and daring. Dressage, as the Spanish Riding School of Vienna, Austria, is displaying it this week at Capital Centre, satisfies as only classical art can. It delights our sense of measure, balance and order yet is also an outlet for that wild urge to rejoin nature, become one with the animal world and submit instinctively to the forces of motion. No wonder, then, that the audience for these performances includes outdoor types and sports fans as well as the social set and dance lovers. At Thursday's opening, diplomats were added to this assortment, presided over by Austrian Ambassador Friedrich Hoess and his wife, Clair.

For anyone who has seen the Spanish Riding School before, part of the wonder of this institution is that so little changes. The riders are dressed as their predecessors a couple of centuries ago were, in chocolate frock coats and cream breeches. With gloved hands they doff their domed, two-cornered black caps each time they enter the arena. And the riders themselves are reserved. It is the horses who may express temperament -- a snort, some foam at the bit and a wildness in the eyes.

As in ballet, there is much emphasis on precise foot- and legwork. Carriage and direction of the head and neck, though, can vary the steps imaginatively. In some classroom pieces, the trainers stand beside their horses and guide them with short hand-reins on the open ground or between two posts.

There was an impressive demonstration of long-rein work by Norbert Tschautscher (first chief rider) and the large, powerful Conversano Roviga. Strength, smoothness and timing combined so richly in this set that one wonders how it would work if it were performed to solo violin music by Bach. Much of the accompaniment for the Lipizzaners consists of efficient potpourris of 19th-century marches, polkas and waltzes. The single exception was a pas de deux for a sire-and-son pair of horses, Siglavy Plutona and Siglavy Europa II, with Johann Riegler and Kottas as the riders. While elegant in its mirror images and other symmetries, as choreography this work lacked the deeper dimensions of its score, the first portion of Mozart's 40th Symphony. Another solo of school steps, performed by Klaus Krzisch on Siglavy Mantua I, seemed so musical that it might have been a better candidate for something other than marches.

The program's climax was the "School Quadrille," a superbly and serenely crafted piece of classical riding and choreography. All facets -- the steps, the carriage, timing, changes of direction, control and fantasy -- showed their measure.

The Spanish Riding School, directed by Jaromir Oulehla, gives its final performances here tonight and tomorrow afternoon.