Last Saturday's concert at Tanglewood by the Israel Philharmonic was marked with distinction both before and after the actual performance.

Part of the hype surrounding the guest orchestra's appearance was that soloists Itzhak Perlman and Pinchas Zukerman were recreating their 1982 recording (on Deutsche Grammophon) of Mozart's Sinfonia Concertante for Violin and Viola, K.364, again under Zubin Mehta. But after the Mozart had been played, Perlman and Zukerman played an unexpected encore that astonished the crowd.

The concert began with Brahms' "Variations on a Theme by Haydn," Op.56a. With modest phrasing and understated conducting by Mehta, the orchestra seemed comfortable with the vaguely religious character of the piece. The second variation, in which accented downbeats in the strings set off flowing motion in the winds, best manifested the gentle and evolving tone.

At times, Mehta seemed constricted by the serene monotony of the music. Finally, in the last variation, he was able to bring down triumphant chords from the strings and brass that resembled those Brahms employed in his emotional Violin Concerto.

Unfortunately, the climax and finale of the piece did not expand the whole but only continued it in predictable progression. The horns seemed to disappear by the end of their solos, and the bells did not really blend into the full landscape of the climax. Mehta later proved that the Israel Philharmonic was capable of true force, but here the power of a Brahms finale, even of such a relatively inconsequential piece, was noticeably lacking.

After a short break, Perlman and Zukerman came on the stage to tremendous applause. Mehta waited for the welcome to end, and then joked around with the soloists a bit while they turned. This was not the best of nights for an outdoor concert, because the temperature was dropping noticeably throughout the evening. Nevertheless, Perlman and Zukerman gave an outstanding performance.

A quick tempo, an indication of things to come, was chosen for the first movement. The soloists approached their task in different ways; Perlman played very methodically and correctly while Zukerman, playing with confidence on an instrument that carried beautifully, strove to come out when he had a melodic line.

One of the curiosities of Saturday's reading of the Mozart was a slightly uncoordinated set of slides that seemed to date the performance before its time. In his first playing of the main theme, Perlman slid the third pair of notes and was followed dutifully by Zukerman. However, in the recapitulation of the theme, Perlman also slid the second pair, and was not echoed by his partner.

The slow preceding section of the first movement also showed some difference of interpretation, as Zukerman took his again echoing part a bit faster than Perlman had. Zukerman showed his spirit for the outdoor concert by turning to spread his long notes over the whole audience. In the third movement, Zukerman again failed to follow Perlman in his rather unusual (for contemporary recordings) sliding in the first major theme.

Mehta and the soloists took the second movement a shade fast, but there were some pleasant surprises. Perlman showed his strength by hitting his high notes even better than he did on the recording. He also pulled off an amazing feat by constantly keeping even with Zukerman in volume despite the difference in their instruments timbre and size in this microphoneless (in the theater, not on the lawn) atmosphere.

Perlman's reading became touching as he seemed to approach it less formally than he had the first movement. His playing was marred only by a quickly corrected tendency to sound flat on his longer notes that was probably a result of the changing temperature.

The tempo stood out again in the third movement as the soloists streaked to the end of the piece. Zukerman, finally able to speak fully in the broad chords of the second motif, was visibly enthusiastic. Perlman read the third movement flawlessly and contributed in volume and exuberance to the finale. Zukerman bit off a bit more than he could chew with his last low chord, but the mistake was hardly noticeable. In any case, the end was greeted by a lengthy and well-deserved standing ovation.

The real story of the evening came minutes later, when Perlman and Zukerman quieted the crowd by resuming their places center stage. As the reduced (for the Mozart) Israel Philharmonic sat by silently, the soloists commenced a reading of an unbilled marvel of virtuosity and musicality, the Handel Passacaglia arranged for violin and viola by Halvorsen.

As the people sitting on the lawn and the sides of the main theater slowly gravitated towards the stage, Perlman and Zukerman spun out dizzyingly fast and perfectly crafted notes in what seemed to be two parallel and inexorably linked sonatas rather than a duet.

The concentration of the artists and the audience lay heavy in the air as the other-wordly music floated out from the dais. When Perlman embarked upon a section that featured precipitously falling thirty-second notes, much like their counterparts in Prokofiev's Violin Concerto, a few gasps of awe and pleasure could be heard.