The Tanglewood triumphs of Klaus Tennstedt and Yo-Yo Ma

Last weekend at Tanglewood, summer home of the Boston Symphony Orchestra, something rare happened: All three concerts were profound performances, suffused with unusual musical insights. Klaus Tennstedt conducted two of the programs; in the other, Yo-Yo Ma traversed the Dvorak Cello Concerto to predictably glorious effect.

Tennstedt's American career began at the Boston Symphony in 1974 with concerts devoted to Brahms and Bruckner. He had recently defected from East Germany and had no reputation whatever in the West. Those two BSO concerts were a wild success, and his international career was instantly launched. He has since had his ups and downs with this orchestra, with other orchestras, and with critics.

Tennstedt never entirely decides what he wants to do with a piece until he is on the podium, baton in hand. He is a conductor of impulse and instinct. True, he spends a lot of time in rehearsals working on balances, on the overall sound he wants at each given moment. His impulsiveness is more a matter of deciding how all those moments will be strung together and in what tempo. That is something he often decides on the podium. (It's why his recordings are so often less exciting than his live performances, for that impulse is hard to capture in a studio.)

This has been known to lead to problems - and in the case of a Mahler Third Symphony with the Philadelphia in New York last season, outright fiasco. There he seemed to lose his ability to react meaningfully to the music, and the more desperate his attempts to get back into the groove, the worse matters became. But this sort of trouble has been the exception in my experiences with Tennstedt. And at least he is willing to take risks.

Last weekend was the glorious other side of the coin, in two hefty works by the composers clearly most dear to his heart - Bruckner's Fourth Symphony and Brahms's ''Ein Deutsches Requiem'' (''A German Requiem''). In both works, he gave the music time to breathe, time to unfold. And he apparently persuaded the orchestra members to trust him, so even if their ensemble was not always exemplary, the spirit of the performance carried them through.

I can think of no other conductor today who understands and communicates the essence of Bruckner like Tennstedt. The composer heard a certain concept of size and time, and if a conductor tries to rush the piece, it ends up sounding sporadic, fragmented, and at times even trivial. Tennstedt shows us the value of the well-chosen, deliberate tempo, for suddenly the tensions between loud and soft, between tempestuous and radiantly calm, become tangible.

The fragmentation of thematic development, and the unusual use of pauses and silence, are all a part of the Brucknerian plan that too many conductors do not understand, do not feel. Many conductors cannot relate to the idea of a composer's using his music to dramatize his faith in the Almighty as Bruckner did.

Here was a Fourth rich in orchestral color and detail, written by a man who knew exactly what he wanted and how to get it. The full breadth of the drama unfolded with stunning impact, and Tennstedt kept the fragile continuity taut throughout.

Brahms's ''A German Requiem on Words From Holy Scripture'' is much praised and much loved. But its particular beauties, its power to move, remained a mystery to me until Tennstedt's bewitching interpretation. This requiem doesn't dwell on death, but on the expectation of peace and comfort for those who would mourn. Brahms had, according to the informative program note by Michael Steinberg, wanted to call it ''A Human Requiem.'' And, indeed, humanity is what set this performance aglow.

Tennstedt's tempos were uncommonly slow, and one might have thought the piece would bog down in them. Despite the deliberate framework, the conductor did not come to the piece with a preconceived sense of the mood of the work and try to make each section fit into it.

Rather, he let every section have its own radiant identity. Sometimes there was suffering, sometimes there was sadness, sometimes there was ominousness - and throughout, a true uplift from the scriptural texts Brahms had chosen as a message of hope and peace.

It was all done without theatrics, without an effort to create effects, just as Brahms scrupulously planned it: Even the Judgment Day music is moving, but neither raucous nor showy. The balances within the orchestra sounded remarkably clear. The winds were heard within that fabric of sound in a way that's rare in this brass-heavy age.

The orchestra itself played as a foundation to the chorus, which Tennstedt rightfully saw as the focal point of the work. It had to blend with the chorus rather than have the two fight it out. The Tanglewood Festival Chorus - under the direction of John Oliver - gave Tennstedt a performance of uncommon potency. Rarely have I heard it (or any chorus) sing with such fervor, such a variety of shadings, and such a sense of conviction.

In both works, Tennstedt seemed to pull a veil from an often-heard work, and the results were revelatory.

Cello concerto

Two weeks ago I wrote about the issue of heart in musicmaking, as heard in the work of cellist Yo-Yo Ma, and here he was at Tanglewood, performing the Dvorak Cello Concerto in typically superb fashion.

His insights into the piece, particularly the melancholy/wistful side, are uncanny. They are delivered with maximum impact and without emotional excess. Everything Ma does is tasteful, including the discreet use of portamento (sliding from one note to the next). Until a few years ago this was anathema to the modern school of string playing. Ma shows what a large amount of communication is lost without it. His ability to move the listener to tears, then to elation and joy, is a special gift.

BSO music director Seiji Ozawa was attentive to Ma's playing, though at times not quite as alert as one would wish.