PART OF the dream for any young musician is to have an enthusiastic audience. Since 1979, the members of the Lettumplay Youth Ensemble have realized that dream every summer through an extensive series of free concerts in the Washington area. Organized by the late Tony Taylor, the Youth Ensemble originally did concerts for a target audience of preschoolers through teen-agers, but in recent years they have been doing many concerts at hospitals and centers for senior citizens, as well.

"We'll be rehearsing during the early part of this week," says Bob Wilson, executive director of Lettumplay, a nonprofit community arts organization dedicated to the preservation and dissemination of jazz. "On Friday, we'll perform at D.C. General Mental Health Area C, a noon-day performance. There also will be a noon concert at Farragut Square on the 18th, and a picnic for senior citizens at the Frederick Douglass Home on the 21st; that's with a group called Charisma as part of YES--Youth Entertaining Seniors." Other concerts will be held at Lorton Reformatory, the Washington Center for the Aging and Lincoln Park (the Ensemble also will open for vocalist Nancy Wilson at the Carter Barron on Aug. 12).

On July 26, the Ensemble will fulfill one of its favorite yearly obligations with a concert at Children's Hospital. "One musician writes a special piece for this concert every year and dedicates it to the children," Wilson says. "Ron Sutton Jr., our lead alto saxophonist, wrote a piece last year called 'Animated Rhythms,' a collage of seven cartoon themes which he took and put into a jazz version of each tune. The kids would recognize the head main theme of the tune as what they'd hear when they were watching cartoons, but then they'd hear variations, which was a different sound. It's great for these kids to hear music they hear every day but realize there are different ways of doing it."

Some of the musicians in the Ensemble recently have been kids themselves, Wilson points out. The age range is 16 to 21, with participants drawn from Lettumplay's ongoing music programs, the Duke Ellington School for the Arts, Howard University and elsewhere. For example, drummer Winard Harper is a student a Howard. His younger brother Phillip just graduated from high school in Atlanta and is in Washington for the summer (he'll be playing first trumpet).

"This year is the biggest band that we've ever had," bubbles Wilson. "We're using two trombones, three saxes, two trumpets, piano, bass, guitar, drums and synthesizer on certain tunes. We're doing a mix of original arrangements and some standards that the musicians have taken and rearranged. There's even a 'Lettumplay Theme' that was written by Snooks Reilly." The musical director this summer is Atiba Bakr, a multi-instrumentalist on reeds and a recent graduate of the highly respected jazz studies program at Howard. "He's been doing some rearranging of tunes to fit the complement of musicians we have this summer," explains Wilson.

Bakr, at 26 the elder statesman in the Ensemble, has had some student teaching experience and views his leadership role as "a great professional and learning experience. Even the young players in the Ensemble are very good. They don't have a lot of experience but they have a lot of promise and we have several experienced players--the Harpers, Ron Sutton, myself--for a backbone."

The Ensemble has been rehearsing for a couple weeks, though some players already were familiar with each other from playing around town together."When the opportunity arises we put together a basic ensemble to do performances when we're requested," says Wilson. "But when they go before the public, they want to do so as a well-prepared group and not just anybody playing together for the first time; that's the kind of dedication these young people have."

Dedication will be a prime commodity this summer because funding for the Ensemble's series of 23 concerts has run into some unexpected snags. A grant from the D.C. Commission on the Arts and Humanities was much smaller than requested and an expected grant from a local utility company fell through at the last minute. "We had a budget of $20,000, and we're $16,000 short of that," Wilson sighs. "Our staff is working knowing they may not get paid, but they too have dedication. We will suffer individually, but the program is not going to be cut back. We've made a commitment to the community and we're going to keep those commitments.

Wilson envisions the summer concert series concluding with the first Lettumplay Youth Jazz Festival, to be held at the Sylvan Theatre on the Washington monument grounds sometime around Aug. 20. "There are six programs besides Lettumplay doing summer programs in music," he points out. "Our concept is to pull all of these individuals together and present to the city a total picture of what was done with the music over the summer period."