The Northern Virginia Youth Symphony Orchestra sounded not merely like a good youth orchestra but like a professional ensemble in its concert last night. Considering the weather, it wasn't easy.

It was 8:20 at the Lake Braddock Secondary School in Burke, and there was no sign of the concert that had been scheduled to start at 8. School-age string players were still hurrying into the little theater, next to a gym where a basketball game was in boisterous progress. "Our first trombone is still missing," someone was saying into a pay telephone. "We can't play Ravel's 'Bolero' without our first trombone."

The second horn and piccolo were also absent -- possibly lined up in the hour-long traffic jam behind a jackknifed tractor-trailer on one of the main roads leading to the school. So were some strings -- but an orchestra can usually get along without one or two violins, even a contrabass, as long as there are others to cover the part.

"We got some indignant calls from parents because we didn't cancel," said a staff member of the orchestra, "but when could we get all this together again?"

"All this" included an orchestra of more than 100 pieces (at least when the roads aren't iced up), two solo singers, a narrator, two conductors and a composer, all of whom had been preparing intensively for a world premiere to climax a program of standard classics. And it was not quite together when the concert began, a bit after 8:30, with the "William Tell" Overture moved into the second spot on the program, after Schubert's "Unfinished" Symphony. The orchestra had all the players it needed for these two works but not enough for the "Bolero" or for the world premiere of "Nature-Life," a symphonic poem by Washington composer Andreas Makris.

Players materialized gradually during the first half of the program (a double bass coming in, for example, between the Schubert and the Rossini), and all the necessary instruments were in place by the time the hastily rearranged program reached its heavily orchestrated second half. By then, playing two of the most familiar works in the repertoire, the orchestra had already shown what it could do.

It was not note-perfect, but extremely impressive. The first horn entry in the Schubert was a delight, and the low strings played with exemplary smoothness of ensemble phrasing and mellowness of tone. The principal cellist was remarkable at the beginning of "William Tell," as were several of the principal winds throughout the program. Under the baton of music director Luis Haza (like composer Makris, a violinist with the National Symphony), the interpretations generated real excitement.

The Makris work explores the theme that to nature, life and death are a matter of indifference. The theme was explained simply in a narration delivered by orchestra manager Anthony Stark, but the music is highly demanding with rich, subtle, constantly shifting textures, tricky rhythms, a lot of exposed solo work for the winds and eerie, high harmonics for the violins. Its complexity sometimes reached a point where a second conductor was needed -- a role ably filled by Gilbert Mitchell.

"Nature-Life" is thoughtful, well-crafted music; it received a powerful first performance, and it was welcomed with warm, well-deserved applause. A set of wordless melodic lines, symbolizing life, death and their harmonization in nature, was well sung by soprano Pamela Jordan and baritone Charles Williams.