Milestone for a maestro. A BERNSTEIN CELEBRATION AT TANGLEWOOD

IT'S no coincidence that Leonard Bernstein came to Tanglewood, the idyllic summer home of the Boston Symphony Orchestra, to celebrate his 70th birthday last week. His ties with Tanglewood and the Boston Symphony go back to 1940, when Serge Koussevitsky launched the Berkshire Music Center here and Mr. Bernstein became that legendary maestro's favorite pupil. Bernstein has maintained his association with this educational arm of the orchestra ever since.

The birthday festivities last Thursday through Sunday were focused not just on Bernstein's many accomplishments but on the Tanglewood traditions he has helped keep alive. Brand-new music and students on their way up played an important part, as they have throughout Bernstein's career.

The Friday ``Evening Prelude'' concert, for instance, was devoted to songs commissioned for the occasion from 12 composers. Sandwiched between symphonies by Haydn (No. 88) and Tchaikovsky (No. 5) on the Sunday program were variations on a Bernstein theme by eight more composers, master orchestrators all. The main concert Friday was a showcase for the versatility and virtuosity of the Tanglewood Music Center's student orchestra. And on Saturday, the Indiana University School of Music presented a fully staged production of the work Bernstein is said to cherish most - the ``Mass'' he wrote in memory of John F. Kennedy.

It doesn't really matter that little of the specially composed music will be performed again (though Michael Tilson Thomas's ``Grace'' could well be). Just the caliber of the composers who took part - Oliver Knussen, Bright Shen, Ned Rorem, Peter Schat, George Perle, David del Tredici, Alvin Singleton, Yehudi Wyner, and Stephen Schwartz, to name a few - signals the respect and affection the musical community feels for this extraordinary conductor, composer, and pianist.

Bernstein, after all, is a musician whose range extends from Brahms to Broadway and who can bring together talents as diverse as Beverly Sills and Patti Austin. His life has had its share of controversy; yet few would dispute that his impact on music has been anything short of remarkable.

The involvement of so many top composers was clearly a measure of the friendship Bernstein has extended to them throughout his career. As music director of the New York Philharmonic, he was an ardent champion of new music. He saw programming it as not just a duty but a mission. He talked about it eloquently and enthusiastically, challenging audiences to really pay attention, even if they might not at first like or understand what they were hearing.

The Sunday variations - composed by Luciano Berio, John Corigliano, Jacob Druckman, Lukas Foss, Leon Kirchner, William Schuman, Toru Takemitsu, and John Williams - sustained a level of wit and orchestral skill that was dazzling. Included were several ``quotations'' from ``Happy Birthday'' and ``New York, New York,'' as well as other music by Bernstein and his friends.

The Friday concert by the center's orchestra, also contained some remarkable moments, particularly the finale to Mahler's Second Symphony, ``Resurrection,'' conducted by Boston Symphony music director Seiji Ozawa. The group had played a demanding first half - of music by Brahms, Stravinsky, and Ives. So fatigue took a toll in the second half, but the vitality, sheer sumptuousness of sound, and utter commitment of the players, together with Ozawa's surprisingly heartfelt reading, made for a deeply moving account.

As for the ``Mass,'' this critic finds it a somewhat dated product of the early '70s, a work too self-consciously iconoclastic, pacifistic, and hippie-fied. Even so, the IU student performers gave it their all, and the audience showered performers and composer alike with boisterous ovations.

The applause was equally thunderous on Sunday, when Bernstein took to the podium to conduct the BSO - and when presidential candidate Michael Dukakis and Secretary of State George Shultz made appearances that set the audience abuzz.

Yet Bernstein's interpretation of the Haydn was so irresistible that one immediately forgot the hubbub. As shown on his superb recording of this work with the Vienna Philharmonic (Deutsche Grammophon CD 413 777-2), he sustains forward momentum while still allowing the suppleness of the melodic line to come through. As a result, we come to appreciate a level of rhythm, melody, and mood too often missing from performances of Haydn.

Bernstein has been rethinking Tchaikovsky lately. His recent recording of the ``Path'etique,'' with the New York Philharmonic (Deutsche Grammophon CD 419 604-2), is 11 minutes longer than the usual performances. Sunday's reading seemed to go on forever, teetering between grand vitality and leaden inertia. Too often, one suspected, Bernstein was examining this music through the prism of Mahler. To these ears, his approach simply put more weight on the score than it could bear.

But at the same time it testified to Bernstein's endless explorations to uncover music's secrets. It is the maestro's ongoing, inexhaustible embrace of music in all its aspects to which the Tanglewood weekend, in its flamboyant and touching ways, paid fitting homage.

Thor Eckert Jr. is the Monitor's music critic.