"My manager turned down an offer from the London Philharmonic last week," Andrew Litton says, smiling into his drink in the Watergate's Peacock Lounge. "That feels good; not turning them down, but being in a position where I could, where I had to."

In London, where his manager sometimes has to say no, Andrew Litton is "that 25-year-old American Wunderkind," a brilliant young conductor and sometime pianist who appears regularly with the Royal Philharmonic and occasionally with other orchestras. In southern France, he is an "heureuse de'couverte" ("happy discovery"). In Washington, where he lives, Litton is almost unknown except to hard-core music fans, children and devotees of the National Symphony's pops concerts.

That should change tonight when he raises his baton for Carl Maria von Weber's "Euryanthe" Overture in the Kennedy Center Concert Hall. It will be the 61st concert in which he has conducted the NSO but the first in which he was regularly scheduled for the orchestra's subscription series.

Litton is an apprentice, supported by grants from Exxon and the National Endowment for the Arts, now in his third year with the National Symphony Orchestra and learning his trade as a conductor. The Exxon/National Endowment program is designed to remedy the most serious problem facing young conductors: If you are a pianist, you can usually find an instrument to practice on; but what do you do if your "instrument" is a symphony orchestra?

"A lot of it is vicarious conducting," Litton says. "You sit there at a concert or rehearsal, watching how someone else does it and thinking of how you would do it differently, resisting the temptation to run up to the podium and grab the baton."

Until tonight, Litton was supposed to have a low profile, and he has managed that fairly well in Washington, with one major exception, when NSO music director Mstislav Rostropovich took ill and Litton filled in at the last minute. His job is to attend concerts and rehearsals, observe the style and techniques of other conductors who work with the orchestra, conduct the NSO in family, youth and pops concerts, and get ready for the Big Day when he steps into the spotlight to conduct a subscription concert.

That big day, scheduled 14 months ago, is Dec. 6, 1984.

Having devoted his Washington career largely to youth concerts, Litton claims to like them -- though perhaps not as much as the spotlight of the subscription series. That is just as well, since he will be conducting 10 of them in five days next week, after his brief moment in the spotlight.

It was at a New York Philharmonic youth concert, conducted by Leonard Bernstein, that 10-year-old piano student Andrew Litton first decided he wanted to be a conductor. "I hope that at one of my youth concerts, somebody in the audience will catch the fever the way I did," he says. The music that made him want to be a conductor was Respighi's "Pines of Rome," which will conclude his debut concert tonight.

Now that a London critic has compared him favorably to Bernstein, Litton can be philosophical about youth and pops concerts. "Every time you give an upbeat and a downbeat, it is a valuable experience," he says. He also adopts a cheerful air about the limited rehearsal time available for such concerts: "To have to put together a program in one rehearsal: that is what we call learning efficient rehearsal technique, and it is a valuable skill. Rehearsal overtime is frowned on by all parties concerned."

A few funny things have happened to Litton en route to his rendezvous with destiny tonight. First, he won a conducting competition, sponsored by the BBC, three years ago and that launched him on a promising conducting career in the British Isles. Then he filled in for Rostropovich, conducting the NSO in Schubert's Ninth Symphony and MacDowell's Second Piano Concerto. That was in March 1983, and he had only two days to prepare the program.

Last month in London, another Russian conductor, Yuri Temirkanov, was stricken ill. Temirkanov is the principal guest conductor of the Royal Philharmonic, where Litton has been conducting a couple of weeks per year since January 1983. "The Royal called and asked me, 'Can you come and help us out?' " Litton says, "so they wound up flying me over on the Concorde, which was nice; I must say it's ruined me for life."

Litton was in France, rehearsing for his debut with the Orchestre Philharmonique de Nice, when the emergency struck the Royal Philharmonic on Nov. 10. On the 17th, he flew from Nice to London, rehearsed the orchestra and substituted for Temirkanov in two different programs on the 19th and 21st. Then he had to take the Concorde back to Washington on the 22nd; he had a date to conduct the NSO and the McLain Family Band in pops concerts on the 23rd and 25th. On Nov. 26, he flew back to London for a series of concerts with the English Chamber Orchestra and the cello soloist -- Rostropovich. He flew back to Washington on Dec. 3 and began rehearsals at 10 a.m. on the 4th for this week's subscription concerts.

After a month in the musical jet set, Litton muses, "I don't know how Slava does it."

Some of the works Litton conducted during the whirlwind of the last month were pieces he had never conducted before. At 25, it could hardly be otherwise. He prefers not to discuss the limitations of his repertoire, but admits that his premiere performance of Elgar's "Enigma" Variations was given with the Royal Philharmonic on Nov. 19. But he managed to convince the London critics -- as hard-nosed a group as any city in the world can claim.

"Conducting such a work in London really is a matter of entering the lion's den," said Edward Greenfield in the Guardian. "Yet Litton . . . gave the impression that he had been conducting Elgar all his life." The interpretation was not "exaggerated in a Bernstein way," the critic said; it was "a reading as authentic as any I have heard in years."

Although he has committed himself to conducting and claims that he seldom has the time (or the inclination) to practice the piano, Litton has not entirely given up the piano. He plays chamber music in Washington occasionally with other members of the NSO (the next performance will be Beethoven's "Kreutzer" Sonata, 10 days from now on Beethoven's birthday, with NSO concertmaster William Steck). He is also developing some specialties for piano and orchestra in which he can conduct from the keyboard. He did that with "Rhapsody in Blue" in London in October and the response was enthusiastic. Now, he is thinking of doing it with Ravel's Gershwinesque Concerto in G and looking for other pieces with similar possibilities.

Besides his English and French careers (soon to be augmented by an Italian debut), Litton has a small orchestra in the Washington area, the Virginia Chamber Orchestra, to take up his spare time. In spite of all this, he can still give you a self-mocking smile and say: "The most athletic thing I do is wonder where I will go for dinner."