Others may be more prestigious, and some are certainly more affluent, but no musical institution in the District of Columbia is more important than the Youth Symphony Orchestra, which celebrated its 30th anniversary yesterday with a gala concert in the Kennedy Center Concert Hall.

The music was quite variable among the half-dozen orchestras that took turns on the stage, ranging from a swarm of tiny tots who fiddled their way through "Twinkle, Twinkle, Little Star," Suzuki-style, to the large and highly proficient alumni orchestra, which gave brilliant performances of Copland's "Appalachian Spring" and Tchaikovsky's "Capriccio Italien" under the baton of Michael Morgan -- assistant conductor of the Chicago Symphony and one of the program's most successful graduates.

Figures given out at this concert speak for themselves: The program has had nearly 50,000 participants in its 30 years; the orchestra often has toured overseas to such places as Japan, Taiwan and the Soviet Union; alumni are playing in most of the major American orchestras and foreign orchestras in location ranging from Brazil and Canada to Germany, Austria and Israel. It has trained 25 percent of the minority musicians working in American orchestras.

The music was generally good -- in proportion to the level of the players in the various orchestras. Lyn McLain, the founder of the program and an excellent educator-musician, modestly took the Preparatory Orchestra through a slow, careful performance of variations on the "Ode to Joy" from Beethoven's Ninth Symphony, and the Elementary Orchestra through two adventurous excerpts from Tchaikovsky's "Nutcracker." The Junior Orchestra, under Kenneth Whitley, played with considerably more power and precision in Heikki Suolahti's pungent Sinfonia Piccola and Copland's "Hoe-Down," and the Youth Orchestra, directed by Alfonso M. Pollard, gave excellent performances of Warlock's "Capriol" Suite and Tchaikovsky's Festival Coronation March.

But musical quality is not the only consideration. Morgan, who is working on similar programs in Oakland, Calif., and Chicago, put it succinctly in a recent conversation: "A strong arts program in the schools would be a better investment than bars on the windows and metal detectors in the halls." The poise, dignity, enthusiasm and self-discipline shown by the students in this program were graphic illustrations of what he was talking about.