By 1971 conductor Klaus Tennstedt had reached 45 and had clearly had his fill of life under the communist regime in East Germany. Like so many of the finest artists of the Eastern Bloc, he bolted to the West. Thanks to an official's misapplied rubber stamp, he got an exit visa to Sweden, and his wife followed a while later.

Tennstedt, who opened the National Symphony's Beethoven festival last night and will conduct there again tonight, had modest career expectations. "When I made my escape," he remarked in an interview this week, "I thought that after a few years in West Germany I would get a good position with an orchestra or an opera company. But I did not expect that I would ever get one of the prominent ones."

Now, 11 years later, he is as much in demand by the greatest orchestras as anyone except perhaps Karajan, Bernstein or Solti. He is a prodigious recording artist. He conducts the Berlin Philharmonic -- the finest German ensemble -- for more weeks a year than anyone else except its music director, Karajan himself. He is about to replace Sir Georg Solti as the London Philharmonic's music director. And soon he will resume his career as an opera conductor -- something he had left behind in the East -- with Strauss' "Elektra" in London and Beethoven's "Fidelio" at the Met.

It seemed clear when Tennstedt left East Germany that he did so more to get away from intolerable circumstances there than to seek what turned out to be richer fortunes elsewhere. Yet the one subject the normally outgoing Tennstedt won't talk about for publication is his motive for leaving his native country. When asked about this, he gesticulated strongly and spoke with great intensity, "Please, please, I just cannot talk about that. You know, my friends are still there. Even my mother."

Certainly Tennstedt has been persona non grata to the East German regime since his departure. He sees old friends, such as conductor Kurt Masur, when they tour in the West, but he cannot return to East Germany. "I hear that there have been efforts to invite me back to conduct," he noted, "but nothing has come of that. Before these kinds of things can happen there, much time must pass."

Unlike such celebrated emigre's as Rostropovich or Makarova, Tennstedt had to build his career in the West from scratch. "I didn't know anybody and nobody knew me," the tall, blond, blue-eyed Tennstedt declared as he sat in his Kennedy Center dressing room after a rehearsal, puffing away on a British cigarette.

Tennstedt rose to the top on the strength of his formidable talent and his specialty: the central European symphonic tradition of Beethoven, Brahms, Mahler and Bruckner. He arrived at the right time on the international scene. The most revered figure in this school of conducting, Wilhelm Furtwa ngler, died a generation ago. And other major conductors of this style -- such as Bruno Walter, Otto Klemperer and Karl Bohm -- have died in the intervening years. Even so important a German as Karajan mixes the German style with the primary alternate, the kinetic, lean manner fathered by the late Arturo Toscanini (this is the style that has dominated conducting here in recent decades). Perhaps Tennstedt's very geographic isolation during the years he matured as a musician kept him from being more influenced by international styles.

His career in North America began almost by accident. The manager of the Toronto Symphony heard the "unknown" conductor during a trip to Europe in 1971, and hired Tennstedt to conduct that orchestra. News of that remarkable debut reached the management of the Boston Symphony. The upshot was two weeks of concerts in Boston in December 1974 that created such a sensation that since then things have never been the same for Tennstedt.

The National Symphony would like to have Tennstedt as much as it could get him. The problem, said NSO executive director Henry Fogel, is "that everyone wants him. I would be happy to get him for four weeks a year, but that's the time he's giving to the New York Philharmonic, and then there's three to Philadelphia, and some to Cleveland and so on. My real goal is just to ensure that we get him at all. He has been worried, for instance, that there may not be enough rehearsal for these programs. So I told him to take all the overtime he wants. I don't say that to most conductors, but I want to keep Tennstedt happy."

For his part, Tennstedt regards the National Symphony as "a very good orchestra." He conducted it for a week some years ago, and now finds it to be "more flexible, and that is very important. Now it seems that everybody in the orchestra likes to work. It has reached the point where you have no big problems, and everybody can concentrate on the music."

But inevitably, now that he is taking on the London Philharmonic, he will be conducting less in the United States. "I cannot stop conducting the American orchestras, though; they are simply too good," he exclaimed. "I think it is not possible to have a bad orchestra in this country. There is so much talent and the system is good. In Germany, that is not the case. There are so many orchestras, and some of them are very bad. But if they are financed by the government, they will go on anyway."

Another link he insists on preserving is his relationship with the Israel Philharmonic, an ensemble that does not often invite a German to conduct. "I went there for the first time with some trepidation. It's a little funny. I thought, 'They do not know me. And, for all they know, this man is just old enough that he could perhaps have been a Nazi.' But everything went beautifully from the beginning. And it especially delights me that what they want me to conduct the most is Mahler," who was himself Jewish.

The only problem Tennstedt has had in his meteoric rise, he noted wryly, had to do with a pastime: hot-air ballooning. "I go up about 2,000 meters, and nothing could be more safe. And when you get up there it's the only moment in your life that is absolutely quiet. Even in some flying and in sailing you have the wind. But in the balloons you go with the wind, so you don't hear it."

Nonetheless, the London Philharmonic's management had its doubts. It suggested that some limits on the ballooning go into Tennstedt's next contract.