With the magnificent conducting of Klaus Tennstedt last night, the National Symphony's three-week Beethoven festival could hardly have gotten off to a grander start.

There is not a finer Beethoven conductor than Tennstedt. Because he had not performed in the West until he defected from East Germany a decade ago, his name is still not as famous as some of his colleagues'; but stardom for Tennstedt is only a matter of time.

At the end of last night's version of the "Eroica" Symphony, the reaction of the large Kennedy Center Concert Hall audience seemed almost hysterical, with the kind of screaming ovation usually reserved for someone like Vladimir Horowitz. Perhaps only Leonard Bernstein, among Tennstedt's contemporaries, has a comparable gift for generating excitement in an audience.

Of the "Eroica's" many claims to greatness, one is that no other work is a surer test of a conductor's interpretive acumen. It is doubtful that any other work crams so many significant musical events into 45 to 50 minutes. At the same time, no symphony has a nobler overall design. The immense challenge to the conductor is to do justice to the wide range of episodes without losing sight of their place in its grand framework.

The intensity with which Tennstedt pursued both objectives last night was breathtaking. Here is a conductor in the hallowed Germanic tradition who is willing to let an occasional secondary detail go awry in order to concentrate on the main musical line and its subordinate elements -- always trying to keep the central idea in the sharpest focus.

But unlike the work of some of the conductors in that style, Tennstedt's performances are anything but stolid and pedagogical. Last night's "Eroica" throbbed with a freshness and vitality that any of his colleagues would be hard-pressed to match. He showed a sure feeling for the ebb and flow both of individual sections and of the overall work. His steadiness of pulse is remarkable. His sense for the right texture of a particular passage is superb.

The man's baton technique is idiosyncratic, to say the least. Sometimes he will barely beat time at all, and he will go for long times without subdividing his beat.His gangly arms flail all over the place. Yet he so utterly radiates musical authority, and gives such an impression of knowing exactly what he wants, that the orchestra is right with him.

After only four rehearsals, Tennstedt had the National Symphony sounding like a German orchestra, and a very good one at that. There was a depth and richness in the bass and in the brass that was new for the NSO. The orchestra's horn section, in particular, sounded superb. The solo horn repeat of the opening theme of the first movement, when it returned in the recapitulation, sounded glorious. And the treacherous horn calls in the scherzo were perfection. In fact, the whole scherzo was perfection, with beautifully judged tempos and execution.

The opening "Coriolan" Overture was in the same interpretive mold. Rudolf Firkusny played with lyric understatement in the second piano concerto, but that delicate little concerto was slightly overwhelmed by the blockbusters that surrounded it.