The philosophy of the Harvard Summer Concert Series seems to consist of indulging its audiences with the familiar while at the same time requiring that it ingest increasing amounts of the new and not so easily palatable. Pianist Leonard Shure opened the series with a completely traditional program of Chopin, Schubert and Beethoven; a week later Jamie and Ruth Laredo deferred to general taste with Bach and Beethoven, but managed to sneak in the somewhat post-Romanticist Sonata Concertante of contemporary Leon Kirchner; last night violinist Felix Galimir and his chamber ensemble (one almost expected the program to read "Felix Galimir and guests") went even further: avoiding the 19th century entirely, the group plunged right in with two works of extremely modern idiom, both composed within the last two decades.

First on the program was the Quintet for 2 Violins, 2 violas and cello (1958) of Roger Sessions. The work is in three movements, nominally conforming to the standard fast-slow-fast alternation of classical sonatas. The first ("Movimento tranquillo") seemed to be written for violin solo with string accompaniment, which might be a function either of the composer's intentions of the energetic playing of Mr. Galimir. The second movement ("Adagio ed Espressivo") exploited the high register of the violin, giving the music a strongly passionate flavor; after a while, however, the emphasis on extreme registers began to wear (at least on these untutored ears) and passion passed over into hysteria. The last movement, ("Allegro appasionato.") was a curiously dance-like finale with its predominantly triple meter (this, too, is a bit of heritage from the musical past) and was quite lighthearted compared to the general severity of the piece. Throughout the Quintet composer Sessions demonstrated a fantastic command of string emsemble sounds and effects: the use of block chords in the four upper strings underlined by 'cello pizzicato, as well as the fleeting recurrences of muted ponticello, were particularly notable.

In the world of string chamber music, it takes works of great individuality to prevent the subtleties and arcanities of the medium from melting into homogeneity. The String Trio Op. 45 of Arnold Schoenberg is much like the Sessions in outward appearance: three sections of alternating mood written in a deceptively similar atonal style.

But the Schoenberg is in reality quite a different piece. Written slightly over a decade before the Sessions Quintet, the Trio is possibly even more severe in idiom. Where the Sessions is expansive, the Schoenberg is concentrated, pithy, intense. Contrasts are much more frequent and stark, with ferocity and elegy following in close succession in a kind of mosaic sound. Schoenberg's use of effects such as tremolo, col legno and harmonics is absolutely chilling.

If the purpose of the first half of the program was epater le bourgeois, the thought behind the second must have been to send 'em home happy. This was done effectively by Galimir and company's performance of Mozart's Divertimento No. 7 in D major, K. 205. Scored for violin, viola, 'cello, double bass, two French horns and bassoon, the piece provided a refreshing antidote to the solid-string sound that had preceeded it. The preponderance of instruments with low ranges tended to make the piece a bit bottom heavy, but Galimir played as if trying to make up singlehandedly for the dearth of treble companions. He more than succeeded.

As the programs of the Concert Series get more adventurous, attendance at Sanders becomes less enthusiastic, (though those who do come are as responsive as ever). This is too bad, since a lot of important but seldom-performed music is being played. The Galimir group are excellent exponents of works like the Sessions and Schoenberg, and it is well worth anybody's while to hear them perform.