Practice, practice, practice. Rehearse, rehearse, rehearse.

Then, on the big night, most of the people who show up to hear you play are your parents, relatives and friends. And they've all been listening to you practicing for the past two months.

That's life for the members of the D.C. Youth Orchestra. During the past two decades, the orchestra has performed in a dozen countries, winning the praise of critics and the admiration of music lovers from Germany to Japan. Still, the group finds it must struggle to win the support of people in their own home town.

Last week, the Youth Orchestra celebrated its 20th anniversary with a concert in the Kennedy Center Concert Hall. Graduates of the Youth Orchestra, some of whom are now professional musicians, also performed. The house was half empty -- some 900 people showed up -- which the conductor said made the acoustics less then desirable, and orchestra members unhappy.

"The Concert Hall holds 2,500," said Lyn McLain, who founded the orchestra while he was a music teacher at Coolidge High School in 1961 and who has served as its only conductor. "People across the world think these kids are pretty special, yet they're right under people's noses here in Washington and they just won't pay attention to them.

"The problem is audience development," McLain said. "I guess we have weak P.R. We should easily be able to draw 2,000 people."

The Youth Orchestra's first concert, 20 years ago, was given with the D.C. Youth Chorale, which recently celebrated its 20th anniversary with a concert in the Kennedy Center Terrace Theater. Over the years, the Youth Orchestra, which began as a collection of Washington's best high school musicians, expanded into the D.C. Youth Orchestra Program, which includes elementary through high school students from the entire metropolitan area.

The program is a training mechanism that accepts students at the age of seven and teaches them to play half-size violins. Later, they may choose different instruments and compete to play with the seven orchestras and wind ensembles. The Youth Orchestra is the top of the heap -- only those who can perform par excellence may join.

"Educators are raving nowadays about curriculum-based education," said McLain, a laid-back musician, who talks like a hip jazz player. "Man our musicians have known about that for yearrrs . They have to compete with each other and perform at a certain level before they can advance. There ain't no other criteria for moving up, other than your ability to play.

"Many of the kids who come through the program go on to play with some of the top symphonies and orchestras in the country. But those who don't, go on to be tops in whatever fields they choose because they're used to applying themselves to their craft."

Melvyn Prince, 17, a trumpet player and a senior at Wilson High School, said "We always have trouble getting people to come out to our performances. Subconsciously it's going to affect your playing."

"We have special problems with effective publicity because most people don't understand what a youth orchestra is and what it can do," said Sara Green, Youth Orchestra concert coordinator in charge of media relations.

"People say, 'Well, they're just a bunch of kids.' But they're more than that. They're serious musicians. But a major problem is that there are many cases where we should be reviewed by critics, and we're not."

The old Department of Health, Education and Welfare's Office of Gifted and Talented evaluated the Youth Orchestra Program in 1971 and designated it as a "model instrumental training program," said Green. In its 20-year history, the Youth Orchestra has performed in youth festivals in Scotland, Switzerland, Germany, England and Japan. The group will go on a 3-week concert tour to Israel and Greece in August. About $75,000 is needed for the trip. Only $10,000 has been raised so far.

It takes $300,000 to run the program each year. The D.C. public schools provice $150,000; the rest comes from local performances, patrons and parents. The Friends of the D.C. Youth Orchestra Inc. coordinates the rund-raisers.

Raisaing money for the program is always a battle, McLain said. "That's the way it is in this city. We've managed to hang on for 20 years . . . . I hope the next 20 aren't going to be as difficult.