The much-heralded 12-year-old Greek pianist Dimitris Sgouros made his Washington debut at Wolf Trap last night with his American champion, Mstislav Rostropovich, and the National Symphony. Sgouros played the Tchaikovsky First Concerto and made the same kind of brilliant impression as in his American debut with the orchestra at Carnegie Hall in April.

Sgouros has remarkable agility with his fingers, remarkable for any age. And there is no work that needs agility more than the Tchaikovsky, the most famous of all piano concertos. Those profusions of octaves in the first movement that cascade up and down the keyboard like heavy rapids were startlingly clean and even. And the last movement was taken as fast as this listener has ever heard. The orchestra, which played well all evening, was harder pressed by these speeds than the boy.

Sgouros also has power. Those huge chords that open the concerto as the orchestra plays the main theme in full force behind the pianist sounded out powerfully. And all this was from a pianist who looks like the pre-adolescent child that he is.

Obviously, in a 12-year-old, the musical gift is not going to be as refined as the technical one. But he showed considerable interpretive flair. Many inner voices that are crucial to harmonic detail were brought out. There was delicacy when it was called for. And Sgouros grasped with assurance the general shape and direction of the concerto and its component parts.

The 6,000 people in the audience broke into a sustained ovation after the first movement and were pushed to greater heights at the end.

It is problematic what to make of a child who can handle the notes of a concerto more securely than many of our finest pianists. It serves no useful purpose to gush just at the marvel of it all, because when Sgouros reaches full maturity what he could do at this age will be beside the point.

Perhaps the best question to ask is what impression last night's performance would make from a pianist in his or her early twenties, which is about the age at which Van Cliburn swept the Tchaikovsky with this work and Maurizio Pollini won the Chopin competition.

Digitally it would be just as impressive. The performance would seem short though of the interpretive individuality expected of an important artist in his twenties. One would also expect more nuance and variation of tonal color--more sharply contrasting the piano's hard octaves, rich sonorities and tender lyricisms. More would be accomplished by indirection, rather than the head-on confrontation of the work with which Sgouros triumphed last night.

It was clearest how much more Sgouros knows now about power than about subtlety when he played his first encore, Schumann's seemingly innocent little "Traumerei." The performance was direct and straight the way you might do a simple song. But interpretively the work is anything but simple. The delicate balancing of voices, for example, where Schumann sometimes leaves it quite unclear which voice is dominant, eluded Sgouros. But the Chopin etude that followed brought back the boy's bravura.

Rostropovich conducted an all-Tchaikovsky program. There was a particularly delicate and flowing version of the Nutcracker Suite.

And the program began and ended with Tchaikovsky battle music. At the first was the "Battle of Poltava" from the obscure opera "Mazeppa." It shares one theme, the Russian hymn "God Preserve Thy People," with the closing work of the evening, the "1812" Overture. Last night's "1812" performance was all you could ever want--broad, rich, precise and loud, without being strident. It was much better than the one Rostropovich did at the Kennedy Center less than a month ago. The music was meant for the out-of-doors. There were two brass bands and the 16 cannons of J. Paul Barnett, who was brought on twice for bows by Rostropovich.

The Meadow Center's lavish sound system, which Wolf Trap has had to devise in place of acoustics in the temporary structure, sounded splendid.

The concert will be repeated Sunday at 8.