Variety concerts of operatic arias and ensembles tend to be uneven under the best of conditions. Rehearsal time is limited. Some singers are better cast than others.

What can save such events is enough singing of real distinction to make one forget the rest. That is how yesterday's concert by 10 Washington singers at the Kennedy Center went. They joined the Fairfax Symphony under conductor William Hudson. The event was an example of the newly intensified effort by the Washington Performing Arts Society to promote local talent along with the Te Kanawas and Serkins it brings in from outside.

The most celebrated of yesterday's singers was tenor George Shirley, a veteran of the opera world who also teaches at the University of Maryland, with which most of yesterday's performers are associated.

Style and intelligence have always been Shirley's strong points. His voice is neither large nor sonorous, but the way he uses it is impressive. And even in a concert setting, he is a fine actor.

His singing yesterday of Ferrando's glorious "Un aura amorosa" from Mozart's "Cosi fan tutte," which is perhaps the suavest opera ever written, was not terribly suave vocally. But it was impeccably phrased. Shirley's Rudolfo in two ensembles from Puccini's "La Bohe me" was more idiomatic, with wonderful bending of the phrases.

His partner in the great Rodolfo-Marcello duet was baritone Gordon Hawkins, one of the most promising young singers Washington has produced in recent years. Yesterday he participated in no fewer than eight of the 15 vocal parts of the program. This is really some voice -- large, polished, resonant, with outstanding breath control. One telltale sign of its quality, as well as its potential, is Hawkins' ability to maintain its rich timbre from the top to the bottom, loud to soft. He can turn on the resonance just as well at pianissimo as at forte. Also, he is a splendid ensemble singer. He was properly subordinate in the sublime trio "Soave sia il vento" from "Cosi." But when the occasion called for him to break out above the pack, as in the "Lucia di Lammermoor" sextet, he did so effortlessly. Hawkins is not yet a fully formed artist. His "O du mein holder Abendstern" from Wagner's "Tannha user" was beautiful vocally, but showed he should do some careful studying of Dietrich Fischer-Dieskau on fine points of text and phrasing.

The other most interesting singer was soprano Donna Gullstrand, who subbed at the last minute for the ailing Carmen Balthrop. Her Mimi in "Bohe me" was lovely. And it was not her fault that she was cast in the finale of Strauss' "Der Rosenkavalier" with a voice better suited to Sophie than to the Marschallin she sang.

Tenor James McDonald was dramatically strong in the wrenching verdict scene from Britten's "Billy Budd." And soprano Chrissellene Petropoulos was full of bel canto lyricism in "O! quante volte" from Bellini's "I Capuletti ed i Montecchi."

Hudson and the Fairfax Symphony provided able support.