Reprinted from yesterday's late editions.

When it came time for David Del Tredici's "Lobster-Quadrille" on Tuesday night's National Symphony program, guest conductor Aaron Copland came out, turned to the audience, and said, "We have a slight surprise for you."

The surprise was that the young composer was present to conduct his own music, the world premiere of which Copland conducted nine years ago in London on his 69th birthday. Tuesday night marked the first time that Del Tredici had ever conducted the "Quadrille," but nothing in the performance suggested that the composer was not completely comfortable in the less familiar role.

That is saying quite a lot, since it is music full of rhythmic complications - a pair of dances that after being played separately are later played simultaneously - and various other factors not found in a conductor's everyday assignment.

The most unusual feature of the work is the inclusion of a group of five instruments - banjo, mandolin, accordion and two saxophones - that Del Tredici uses as a kind of pops combo at intervals during the piece. Whether by themselves or joined with the orchestra, they make a fascinating effect, both in sonorities and in the kind of accent they provide. The accordion, especially, rarely gets a chance to show symphony audiences the expressiveness and dynamic shadings of which it is capable. Tuesday night's five players, who were not named, played captivatingly.

So did the orchestra throughout the tricky music, which, under the composer's spare but wholly adequate, explicit direction, showed an irresistible ingenuity and wit in its highly sophisticated garb. Now that Washington has heard one of Del Tredici's more than a half dozen works composed on various aspects of "Alice in Wonderland" surely we should be given "Final Alice" before long.

Del Tredici, 41, did not know until Monday morning that he was going to conduct his music at all four of this week's NSO concerts. But Copland, faced with an unusually heavy program, suggested his young colleague take over some of the job.

Copland opened the evening with Samuel Barber's Capricorn Concerto, raising the question of why this distinguished and elegant music comes to our concerts so rarely. With its three soprano solos for winds, flute, oboe and trumpet, over strings, it is a vibrant success. Irving Fine's Serious Song, for strings, makes thoughtful and ingenious use of familiar means. Copeland's Third Symphony was an impressive closing to a superb evening of this country's music.