MUIR STRING QUARTET (Bayla Keyes, Peter Zazofsky, violins; Steven Ansell, viola; Michael Reynolds, cello) with violinists Andres Cardenes, Barbara Scowcroft, violist Mikhail Boguslavsky, cellist Paul Glenn, Cliff Lodge, Snowbird, Aug. 1, 7:30 p.m.SNOWBIRD - Some chamber groups' fortunes vary with personnel changes. Not the Muir Quartet, whose third edition (i.e., with the addition of violinist Peter Zazofsky) bowed locally Monday at the Cliff Lodge, in a concert co-sponsored by the Snowbird Institute and the Nova Chamber Music Series.

For here, in music of Haydn, Brahms and Shostakovich, was the same faultless ensemble and apparent ease of execution, pervaded by a fine-grained sense of what is going on even beneath the surface.

Zazofsky strikes me as a more individual presence than his immediate predecessor, the estimable Lucy Stoltzman, if not Joseph Genualdi, the Muir's original first violinist. Especially in the Haydn - the Quartet in G major, Op. 77, No. 1 - his solos had a personality and point that, even when his was the leading voice, did not overshadow his colleagues.

Thus the opening Allegro was purposeful yet flowing, with a lyrical radiance in which nothing was ever forced. Not surprisingly that same glow suffused the slow movement, as it did the Menuet - actually closer to a scherzo - here strongly sprung and rhythmically alert. And how good to hear both this and the Finale taken at their marking, a double-quick Presto.

Violinist Bayla Keyes took first chair for the next work on the program, Shostakovich's Prelude and Scherzo for String Octet, Op. 11, providing incisive leadership for a group that also included violinists Andres Cardenes and Barbara Scowcroft, violist Mikhail Boguslavsky and cellist Paul Glenn.

Indeed, on this outing the music fairly leapt from the page, in a work whose youthful intensity cannot hide its astonishing depth (at the time of its composition Shostakovich was all of 19). For from the elegiac introduction to the agitation of the Scherzo, these players got it all, encompassing both the dark shimmer of the former and the incendiary thrust of the latter with extraordinary brilliance and sensitivity.

Of Brahms we were offered the Op. 51, No. 1, the first of his quartets to be published. Again the Muir proved as alive to its inner workings as to the outer, in a strongly argued exposition in which only the middle movements betrayed any hint of unsteadiness, intonational or otherwise.

At the same time the music's powerfully subdued dramatic thread was always to the fore, and not just in the controlled eruptions of the first movement. Even amid the recessed contemplation of the Romanze, one sensed a hidden strength, something no less true of the carefully muted cello and viola solos.

This was encored by the Canzonetta from Mendelssohn's Quartet in E flat Major, Op. 12. About which it is a pleasure to observe, as I have in the past about the Muir's Mendelssohn, that nobody does it better.

Wednesday Reynolds will solo in a group of Bach cello suites, and on Friday the quartet will be joined by Cardenes and pianist David Deveau for an all-Dvorak program, polishing off this year's Snowbird Institute Chamber Music Festival.

Starting time for each is 7:30 p.m., with admission $8 at the door.