Within memory of the past decade, the Capitol Ballet -- a unique Washington cultural institution in continuous existence for 15 years -- has never looked better than it did last night.

That the multiracial company, which has always been a special berth for gifted black dancers, can have progressed as far as it has is a tribute to the sagacity, taste and devotion of three people especially -- artistic director Doris Jones; her co-founding partner, the late Claire Haywood; and the present assistant artistic director, Keith Lee, who in the past two years has had a major hand in reshaping the troupe along professional lines. The present complement of 12 dancers is more polished and vivacious, more technically assured, more harmonious as a stylistic unit than ever before.

It was gratifying that the company should have been seen at its best last night, for this was also the occasion of its Kennedy Center debut, and despite the diminutive proportions of the Terrace Theater stage, the ensemble looked extremely good in this luxuriously intimate setting. There was, however, also some painful irony in the situation -- just at this high point of artistic accomplishment, the troupe is being forced by economic pressures to furlough its dancers for a six-week period, in hopes of recouping a stable fiscal stance for coming seasons.

The evening itself may have come partly to the rescue. The performance was a benefit, the joint recipients of which will be the Capital Ballet and Washington Pre-Schools Inc. To aid the cause, Chita Rivera was on hand to give a peppery rendition of the "America" number from "West Side Story" and a vocal ballad as well.

A native Washingtonian who had her first dance training at the Jones-Haywood School, the noted Broadway performer referred to Doris Jones as "my second mother." Also briefly on stage was Channel 7's Renee Poussaint to introduce spokesmen for the sponsoring organizations as well as governmental and diplomatic dignitaries in the audience, including honorary chairperson Effi Barry.

As for the dance program proper, it was an attractive sampler of the troupe's current and future reper toire, leading off with John Prinz's "Emperor Variations," created recently for the Capitol Ballet, to excerpts from Beethoven's "Emperor" Concerto. Prinz (for lack of adequate time, one hears) has chopped up the music in rather ungainly fashion, but the modestly Balanchinesque choreography displays the classical side of the company deportment ot distinct advantage.

Prinz has also restaged Balanchine's "Tarantella" for the troupe in a trickier version that Fred Martin and the strikingly piquant Kathleen Smith danced with just the right blend of cheeky and affectionate bravura. Sandra Fortune and guest artist Sylvester Campbell were in fine form for a performance of the "Don Quixote" pas de deux particularly notable for Fortune's velvety pirouettes.

Keith Lee's "Taking Off," a "work-in-progress" to a Latin-flavored jazz score by David Sanborn, has yet to find a satisfying gestalt, but it's full of promising material like the svelte, lyrical solo so splendidly executed by Michael Lowe at the start.