LENOX -- Guest conductor Hans Graf had barely begun Tchaikovsky's ''Pathetique" Symphony Saturday night at Tanglewood when a huge uproar arose from the lawn behind the Koussevitzky Music Shed. Part of the sprinkler system had been activated, and some of the 3,000 people on the lawn got soaked. For the first time anyone can remember, the Boston Symphony Orchestra stopped playing after a performance had begun, and Graf left the stage.
Within a few minutes, the problem had been resolved, and Graf returned to the stage and began the symphony again from the beginning. The first explanation, from the BSO press office, was computer malfunction, but yesterday BSO managing director Mark Volpe said, ''It was vandalism, probably kids who broke in thinking it was a joke. We're taking this seriously, and the next time anybody tries it, it won't work, because we are disarming the entire system any time we have a concert." Only one group of sprinklers began to spray, and people who had set themselves up in the front section of the lawn were affected. ''Obviously we are very sorry this happened," BSO press officer Sean J. Kerrigan said. ''I don't think any people left the concert, though."
After the symphony, one music lover said on his way out, ''When the sprinkler came on, we thought we were cool because it was headed the other way, but then it started to rotate, and it got us."
Neither Graf nor the orchestra allowed this mishap to interfere with their concentration -- or to dampen their spirits. Graf started again from the beginning and led a performance notable for clarity of design, precision of detail, and fire of feeling. The March brought down the house, as usual, but Graf and the players made the concluding meditative movement at least as compelling.
The concert opened with an elegant performance of Ravel's ''Le Tombeau de Couperin." This suite, transcribed from a piano piece, is pretty close to an oboe concerto, and principal oboe John Ferrillo played with such style and beauty of tone that he earned a solo bow.
But the musical news of the evening was made by mezzo-soprano Frederica von Stade, who sang Ravel's ''Sheherazade," a work she recorded with Seiji Ozawa and the BSO in 1979, and a group of Canteloube's arrangements of ''Songs of the Auvergne."
Von Stade has been singing more than 35 years, and she's winding down her career without a great deal of fuss -- she announced she was leaving the Metropolitan Opera after her final performance rather than before. She still looks and sounds marvelous, though, and she was entirely secure on the sustained high note at the climax of the first Ravel song, ''Asie"; her performance was far richer in verbal and musical detail than it was 26 years ago. The final song about a potential seduction was particularly remarkable because von Stade didn't overdo it, as has become fashionable. The situation was alluring but not tragic -- just a shrug of the shoulder over what might have been. Graf led with sensitivity, and the orchestra played gloriously; von Stade led the applause for principal flute Elizabeth Rowe for her solo in ''The Enchanted Flute."
A quick wardrobe change and von Stade was back for the Canteloube songs, which were full of character and haunting vocal colors. Some singers half her age fake and smear the coloratura of ''Lo fiolaire," but von Stade articulated every note. She is an artist as beloved by fellow musicians as she is by the public, so the applause united orchestra and audience.