At times during the National Symphony Orchestra's concert last night in the Kennedy Center Concert Hall you might have forgotten to pay attention to the music -- when a green-faced villain, brandishing a wicked-looking sword, chased the clown-faced hero across the stage; when a snake came sinuously writhing out of a jar; when a dog with a purple nose wandered into the scene, or two dancing bears gyrated slowly across the stage, staying as close together as a pair of Siamese twins.

The music, too, sometimes threw into doubt the high seriousness of the occasion -- notably Igor Stravinsky's brief, brash "Greeting Prelude," which transforms "Happy Birthday to You" into a sort of Bronx cheer. But it was a special occasion, although it was a one-night-only family concert with free tickets.

Performing for an audience with a high proportion of children, the younger generation took over the orchestra last night, with results that promise a bright musical future. Two brilliant young Washington musicians, winners of last year's NSO Young Soloists' Competition, were featured: clarinetist Luis Baez in Debussy's "Premiere rapsodie" for clarinet and orchestra and 18-year-old pianist Mia Chung in the first movement of Beethoven's "Emperor" concerto. Conducting duties were shared by Andrew Litton and Hugh Wolff, both seasoned conductors although still in their 20s.

Bob Brown Puppet Productions provided the non-musical distractions, acting out the story of Stravinsky's "Petrushka," while Wolff conducted and narrated with a charm and lucidity that recalled the young Leonard Bernstein's lecture-demonstrations of music during the early years of television.

Wolff, who joined the orchestra as its Exxon-Arts Endowment conductor in 1979, has become a familiar and popular figure to NSO audiences and is now its associate conductor. His conducting of Stravinsky, even with the distraction of a rough-and-tumble puppet show on stage, showed once again how well he has earned this status.

Litton; the new Exxon-Arts Endowment conductor, demonstrated a comparable potential in the challenging Beethoven concerto. His gestures were sometimes sweeping but always lucid, and he precisely controlled the orchestra through a range of dynamic nuances, subtle changes of tempo and carefully calculated gradations of texture that brought out solo passages from orchestra members with exactly the right degree of prominence. Above all, even in the towering climaxes, he maintained an exquisite balance between the orchestra and Chung's glittering, beautifully formed solo. In 10 years, when Litton has lived with the "Emperor" and conducted it many times, the stamp of his personality will emerge more clearly in the way he handles this music. Right now, he has all the virtues one hopes for in a young conductor: a detailed knowledge of the music and an easy, total control of its technical demands. He looks like a very significant talent.

The Bob Brown pupets will appear with the NSO again next season in Manuel de Falla's "Master Peter's Puppet Show" under the baton of Rafael Fruhbeck de Burgos. Last night's "Petrushka" included mimes in colorful masks and costumes, as well as marionettes manipulated by puppeteers garbed entirely in black. Their visual style was somewhere between comic strips and children's television, and sometimes their movements were very effective in small details, but on occasion the coordination between their gestures and the music could have been more precise.