Nothing is quite like the relationship between rider and horse. It has been compared to that between master and servant, lover and beloved, muse and artist. Currently, the poetic truths of these analogies are being proclaimed at the Capital Centre, where the Spanish Riding School of Vienna opened its American tour Saturday and performs through tomorrow night.

The inadequacy of all comparisons is that they fail to suggest bristling energy under perfect control, a splendid display of "wild nature tempered." The traditions of Baroque art and Spanish court etiquette, which linger in the style of Viennese equestrian ballet, are ideally suited to celebrate the marriage of human and animal.

In this haute e'cole of riding, it is the horses that shine. With names like Neapolitano Storia and Pluto Stornella, they are as individual as any human dancer. One extends his legs to thrilling straightness, another glides as if on eiderdown. Conversano Roviga is a compact creature capable of great concentrations of energy. Mounted by First Lead-Rider Lauscha, this veritable Baryshnikov of a stallion performed an extended solo of on-the-ground steps with instantaneous changes of pace. Favory Allora, another star of the first magnitude, was guided on the long rein by Lead-Rider Eichinger in a musically exemplary variation. This stallion is reminiscent of Andre' Eglevsky; no current human dancer of ample size is capable of such finesse. Observing this horse, one realizes how varied a single step can become depending on the speed at which it is taken.

With gloved hand and in perfect time with the others, each rider doffed his cap before proceeding to a demonstration or a dance. Throughout the program, which included a mirror-image pas de deux, demonstrations of on-the-ground and airborne steps and -- as culmination -- a quadrille of shifting geometric formations choreographed for Empress Maria Theresa, the riders remained almost aloof. Like the ballerina's partner in supported adagio, these cavaliers are supposed to nearly disappear from view. The Viennese manage it with consummate grace. The birch riding crop is held motionless, there is little visible leg action or tug on the reins, yet they convey mastery of the tremendous horsepower beneath them by perfect composure and precision movement. The longer one watches, the more aware of this mastery one becomes.

The vast and utilitarian Capital Centre is not the elegantly scaled, columned 18th-century palais that is the Spanish Riding School's home theater. Here, huge television screens for close-ups hang overhead instead of crystal chandeliers, and the floor of the arena is spread with sawdusty turf in place of the rich chocolate-tinted Viennese blend of covering. Yet, as soon as the riders, dressed in coffee-colored tail coats with cream breeches, had entered on the white Lipizzan stallions, their stately file made one forget the surroundings, including such distractions as flashbulbs and the constant scramble for popcorn.

The Spanish Riding School is not as fastidious with the music as it is with the aspects of movement. There is a tendency to chop up and rearrange Mozart, Bizet and Chopin to fit Baroque choreography. Of the "new" scores, the light music of Johann Strauss II works best. But this probably annoyed only a part of the huge opening-night audience, which included circus fans, horse lovers, rodeo addicts, balletomanes and diplomats. In their Viennese home, these riders and horses can be seen by only a couple hundred viewers at a time. The Capital Centre, with all its lack of glamor, provided them with nearly 18,000.