When Lyn McLain took the job as music teacher at Coolidge High School in 1956, the office assigned to him was a back room on the ground floor crowded with Junior Reserve Officer Training Corps uniforms. And the band was a few young men who had signed up just to avoid ROTC.

"It was like, 10 percussionists and two flutes and four trumpets and six saxophones, and that was it!" the 62-year-old McLain said with a laugh.

"I looked at {the band} and said, 'What am I going to do with this?' . . . . I probably quit five or six times in the first three or four months."

Well, McLain is still at Coolidge High School. And he still works out of that small room at the back of the building. But the musical group he heads has changed considerably.

It took him four years to turn the ragtag band into the citywide D.C. Youth Orchestra. Since then, the group has grown to four orchestras widely regarded as among the finest in the country, with ensembles that have performed around the world.

The young musicians, ages 5 to 18, number nearly 1,000 a year, 80 percent of them black or members of other minority groups and 75 percent of them from the city. The orchestra's annual budget, funded in part by D.C. public schools, is $500,000.

Youngsters must audition for every level. Instrument rentals cost $25 a year; registration is $75 a semester. And any parent who can't afford that can pay for it in volunteer time, which explains how the program has provided instrument instruction for more than 45,000 students over the years.

"Our professional orchestras have a great, great problem {that} they cannot do anything about. Major orchestras are not going to have what would be considered a reasonable representation with minorities," McLain said. "And they won't until the educational process makes these things available."

On Sunday, Dec. 30, the orchestra will celebrate its 30th anniversary with a special concert at the Kennedy Center that will include a performance by an alumni ensemble.

The concert is practically sold out, most of the tickets going to proud family members and to the hundreds of private supporters the orchestra has attracted over the years.

The soul of it all is Lyn McLain, a no-nonsense instructor who made a conscious choice one night in a lonely bar in Moline, Ill., to devote his career to something beyond the gigs and road trips of a union musician.

Born in Binghamton, N.Y., he was the son of two musicians who was expected to begin piano lessons at an early age and to play a variety of wind and string instruments soon thereafter.

By the time he was a teenager, McLain had settled on the clarinet as his instrument. He even joined a local orchestra that gave summer Sunday concerts.

He received bachelor's and master's degrees in music from Ithaca College, then moved to Greenwich Village in 1951.

"I was a regular union musician . . . . I played in New Jersey, I played 'em in Brooklyn, played 'em in upper Manhattan . . . in the Catskills."

It was a carefree existence on the road, McLain said, playing mostly nightclubs and weddings. But it also lacked something.

He realized it that night after a gig in Moline.

"I heard this guy who was a really great, great tenor sax player, and he was about 55 or 56 and we got to talking afterwards."

Later, he thought: "Geez, you know, here I'm about 24 or 25, and {I realize} I may very well look at this same scene when I'm 56, just like he is, and I don't really want to do that."

A week later he gave notice, drove back to New York and told his agent that he had decided to "do something else."

The something else started with a move to Washington and Catholic University to study under a professor who had written a few operas McLain admired. After about a month, the department dean told him about a job opening for a music teacher at Coolidge High and, after some urging, he went on the interview that won him the position and the ragtag band.

"The first thing I made them do is learn 'The Star-Spangled Banner.' I said, 'If we're going to play at a football game, we're going to play 'The Star-Spangled Banner.' "

For the next four years, McLain actively recruited students in and out of Coolidge, checking the records of new students for hints of musical skills, talking to junior high schools about his program and holding rehearsals after school so more students could attend.

By 1960, he had a band of about 110 pieces and a citywide orchestra of about 65: the first D.C. Youth Orchestra.

As the group grew, so did support. A nonprofit fund-raising group called the Friends of the D.C. Orchestra was formed, and it provides nearly 75 percent of the group's support today.

It wasn't always easy, however.

In 1974, then-D.C. School Superintendent Barbara A. Sizemore proposed bringing the orchestra under the complete control of the school system, arguing that "the basic assumptions of the program are racist" because they placed more emphasis on European music than the music of other cultures.

The school board voted against Sizemore's proposal.

Over the years, hundreds of orchestra graduates have gone on to musical careers as teachers or professional performers. Michael Morgan, the assistant conductor of the Chicago Symphony is one, and Tim Butler, a cellist in the Kennedy Center opera house orchestra is another.

But McLain said the youth orchestra experience is a valuable one for building character and confidence even if a student doesn't pursue music any further.

"We teach to the highest potential of the student," he said between morning practices one Saturday in the Coolidge cafeteria. "We put them at a level that they can function -- and then we push them."

Nsia Opare, a Friends board member with two children in the program, said McLain's students "know they can't put anything over on him, and they respect him."

"He's saying, 'Hey. We've got a serious program here. We're not here to fool around,' " said Claudette Kaba, whose son plays trombone.

McLain said the beauty of the program is that it often asks students to do more than they initially think they are capable of, but then they find out they can do it.

"Once you accomplish something, that can become a habit," he said. "Just as not accomplishing something can become a habit . . . . Kids will really do something if you give them something that they consider worth it."