In the summer of 1950, in a rural setting among the mountains of southern Vermont, a small group of musicians began an enterprise that has substantially influenced the development of musical life in the United States. Pianist Rudolf Serkin, violinist Adolf Busch, flutist Marcel Moyse and a few friends and colleagues started the Marlboro Music School and Festival as a place for musical learning and recreation. It was not a school in the traditional sense, with classrooms where teachers proclaimed truths to students, but a place where young and old musicians would explore the wonders of chamber music together.

Public concerts naturally grew out of such an activity -- in the early years, in a dining hall that was laboriously transformed into a concert hall on weekends. In 1965, some festival participants began touring together during the winter season under the name of Music From Marlboro. Then came broadcasts, recordings and spinoff groups such as the Guarneri Quartet and Tashi, made up entirely or mostly of Marlboro veterans. Other groups, including the Chamber Music Society of Lincoln Center and Washington's Theater Chamber Players, drew some of their membership and inspiration form Marlboro. In short, the festival is a primary reason why chamber music is flourishing in this country today as never before.

In recognition of this impact Sony has issued a "Marlboro Festival 40th Anniversary" series of live recordings that capture much of the festival's excellence, as well as the spirit embodied in a traffic warning near the dining hall: "Musicians at Play." Most of the repertoire on these discs is ultra-familiar, which means that there is plenty of competition. As a matter of personal taste, you may prefer (as I do) Otto Klemperer's courtly interpretation of Mozart's great Serenade No. 10, K. 361 (on EMI CDM 7 63349 2), but the Marlboro performance conducted by Moyse (Sony SMK 46248) is outstanding and is paired with a real rarity: Mozart's Sonata in B-flat for bassoon and cello performed by Alexander Heller and Yo-Yo Ma.

Ma is only one among many Marlboro alumni who have gone on to distinguished careers. Not all the names are as familiar as his, but the Marlboro Festival Orchestra at one time or another has included scores of outstanding soloists and chamber musicians: violinists such as Isidore Cohen, Felix Galimir, James Buswell, Pina Carmirelli, Glenn Dicterow, Jaime Laredo; clarinetists Harold Wright and Richard Stoltzman; flutist Paula Robison. The star quality of the musicians can be heard in performances from 1969 and 1970, conducted by Pablo Casals, that include Beethoven's Symphonies 1, 2, 4, 6, 7 and 8, as well as Schubert's Fifth and Mendelssohn's Fourth and the Bach Brandenburg Concertos and Suites for Orchestra. By its nature, the Marlboro Festival Orchestra is an ephemeral being, created fresh each summer. But in these recordings, the quality of its membership can be clearly heard.

Casals the conductor is a less imposing figure than Casals the cellist. His Bach cello suites are a cornerstone of any serious collection; his Bach orchestral music, beautifully played, nonetheless sounds a bit old-fashioned in the 1990s. But his Beethoven is often exquisite -- particularly, I think, in the even-numbered symphonies, which tend to be gentler and more personal than Nos. 3, 5, 7 and 9. I recommend particularly Sony SMK 46246, which has Beethoven's Fourth and Schubert's Fifth; SMK 45891 with the "Pastorale," and SMK 46247, as much for a luminous reading of Brahms's Variations on a Theme of Haydn as for Beethoven's Symphony 2 and "Egmont" Overture.

But chamber music is what Marlboro is really about, and the flavor of the festival comes across most clearly in its chamber music recordings. Three classics of the 20th century can be heard in fluent, beautifully integrated performances on SMK 46250: Samuel Barber's "Summer Music," Carl Nielsen's Woodwind Quintet, Op. 43, and Paul Hindemith's powerful and playful Octet for winds and strings. The haunting Horn Trio of Brahms, Op. 40, is memorably played by Myron Bloom, horn, Michael Tree, violin, and Rudolf Serkin, piano, on SMK 46249, along with an expressive performance of the Brahms Sextet No. 2 for strings, Op. 36.

In Schubert's exquisite "The Shepherd on the Rock" (SMK 45901), some listeners might prefer a soprano less tremulous than Benita Valente, but the parts for piano (played by Serkin) and clarinet (by Wright) could hardly be improved. The disc's main attraction is Schubert's Quintet in C for strings, music of towering greatness in a performance that lets that greatness show. A departure from the mostly classical top 40 programming in this series is SMK 45901, which contains crisp, poised, sometimes witty performances of Schoenberg's Serenade, Op. 24, and Chamber Symphony No. 1, Op. 9. Those who usually avoid Schoenberg might find this disc surprisingly enjoyable. Now Playing At least half of Mozart's 25 authentic piano concertos are certified, universally recognized masterpieces, but the two in minor keys (No. 20 in D minor and 24 in C minor) have always had a special status for their direct, limpid expression of deep, personal emotion. In this music, Mozart anticipates romanticism with a startling completeness. In the next century, the piano would acquire a couple more octaves and a louder voice, but it would not find anything more poignant to say than what is said in these two concertos. Both have been recorded (on Eurodisc 69000-2-RG) by pianist Justus Frantz, who will be playing No. 24 with the National Symphony Orchestra this week, in performances that are models of modern-instrument Mozart interpretation. Claus Peter Flor, conducting the Bamberg Symphony, is an excellent partner. Discoveries Frankly, I had never heard of Hermann Goetz (1840-1876) or Friedrich Kiel (1821-1885) until a compact disc (Intercord INT 860.367) arrived containing the Abegg Trio's performance of Goetz's Trio in G minor and Kiel's in G major, both for the standard combination of violin, cello and piano. These are modest works, showing expertise within established forms and styles rather than heaven-storming inspiration or brilliant new ideas, but in the Abegg's expert performance they are extremely pleasant listening -- well made, melodious, expressive and imbued with a fine sense of style. They should be enjoyable to anyone who likes the chamber music of Schumann, Mendelssohn and Brahms.

Vincent d'Indy (1851-1931) is not exactly unknown; his recordings fill a few inches of small print in the Schwann catalogue. But his first two string quartets have fallen into almost total neglect, and a recording of them by the Kodaly Quartet (Marco Polo 8.223140) makes one wonder why. The reason may be timing; Quartet No. 1 in D was composed in 1890, a few years before Debussy's Quartet (1893), which revealed a whole new spectrum of sounds and forms available to four stringed instruments playing together. The second dates from 1897, and with its occasional echoes of d'Indy's idol Cesar Franck, it must have sounded hopelessly old-fashioned. Despite good reviews (which often welcome old-fashioned music), these quartets gradually slipped into neglect. Today, when the first quartet has reached its centennial, the question of how stylish they were when they were new seems unimportant. This is music of real substance, solidly constructed, well played and capable of giving a lot of enjoyment.