One can assume that the Kansas City Philharmonic, which made its first Washington appearance Saturday night in the Kennedy Center Concert fan club here to crowd that audito - the attendance probably owes something to a few other fan clubs: those of soprano Eileen Farrell and tenor Jess Thomas, one would guess, and perhaps a contigent for "Tristan und Isolde," which, condensed and presented in oratorio style, supplied the evening's musical fare.

All these fans should have gone those who like opera only with scenery and costumes. But "Tristan" works well enough as an oratorio (a rather profane oratorio, to be sure); close your eyes, and the music provides all the scenery you need.

The music was well served, most particularly by Farrell, who left nothing to be desired in power, accuracy and expressiveness; one or two sopranos may have a slightly richer tone than she now commands, but I know of no voice that can cut through or float atop the rich texture of this score with more thrilling effect.

Jesse Thomas began with slight insecurities of pitch and rhythm, but rapidly improved, and his third-act monologue was splendidly effective. The Kansas City Philharmonic, under the direction of Maurice Peress, is not a spectacular orchestra by contemporary big-league standards, but is a very capable one, rich in sound (I especially liked the low strings), beautifully balanced and subtle in its visit.