What direction should the National Symphony Orchestra take under the celebrated Mstislav Rostropovich?

"That shouldn't be up to the management," says James DePreist, its former associate conductor. "It should go wherever Slava's muses take it. The kind of chemistry that Slava can generate with musicians is something very few orchestras ever get an opportunity to experience. He is intense and emotional in the best sense, and these qualities inspire excellence. This gives the musicians more confidence and they are less cautious about approaching the musical precipice. He's got them airborne; it's an uncommon circumstance and if they just let him go the orchestra will fly."

DePreist is not in town on National Symphony business, though he will meet with Rostropovich before leaving and will return to guest-conduct the orchestra in December.

After four years as the No. 2 conductor here under musical director Antal Dorati, Depreist decided the time had come for him to have an orchestra of his own. Soon he was engaged by L'Orchestre Symphonique de Quebec, which brings him here tonight for its Washington debut at the Kennedy Center.

The Quebec orchestra is Canada's oldest, if less celebrated than its equivalents in Toronto and Montreal. When DePreist arrived two years ago, it was "a good orchestra," she says, "but one that could be improved." And he has set out, on a smaller scale, to bring about in Quebec the kind of gradual upgrading that is the principal legacy of Dorati's seven years in charge here.

What was in 1976 an ensemble of 67 persons is now 75. The season has been lengthened each year and DePreist is introducing many works new to the orchestra's previously slender repertory. Also, he now guest conducts about five months a year, three of them in Europe and Israel.

He recently signed up for three more years in Quebec, but acknowledges tha his next aim is to run "a big orchestra."

In his years here, DePreist usually was an extroverted interpreter, more of the Rostropovich mold than the Dorati. "I grew up in Philadelphia (as the favored nephew of Marian Anderson) and I guess I just came to associate music with the opulence of the Philadelphia Orchestra. I am especially concerned with the emotional content of the music, but only if handled with the requisite technique. Whether Mozart or Mahler, you can't risk incoherent waddling."

At 40 he is, for a conductor, young, and it means "I am receptive to change; and I am satisfied if the message comes through to the audience. You can always go back and clean up a swamp of muddy clarinets the next time.

"And, you know, that's one of the things that's so wonderful about Slava (at 50). He's still a young conductor, with a young conductor's interest - exploring and willing to risk, and change."