Bill Jones, a 50-year-old computer specialist, is the first musician to arrive. He strolls into Morningside House of Leesburg lugging three instruments and trailing a teenage daughter. He is grinning, and you can tell he is excited. His yellow T-shirt says it all: "Bluegrass Rules."

Ellen Gant, who used to work in a Laundromat and can't quite remember how old she is, sits in the same seat every Tuesday evening: front row, just left of the makeshift stage in the crafts room. "I never listened to much of anything," she says as she settles in, but she listens now. It's bluegrass night.

As 7 p.m. approaches and the last tables are being cleared in the adjacent dining room, Christine Ondocin, activities director at the assisted living facility, ushers more residents into the crafts room and makes them comfortable.

Charles Becker, self-described "nut," is not among them. Although he has struck up a friendship with one of the musicians, he remains in his room and is not planning to come down tonight. He is a musician's musician, and this bluegrass business is not his cup of tea.

"I am a crab when it comes to music," he says. Becker, 89, plays the violin, saxophone and clarinet and still writes melodies. A sepia-tinged photograph on the wall shows him with his band in New York in 1935. He prefers the big band music he used to play there and in Atlantic City; he prefers the chorus girls who were better drinkers than dancers.

"They mean well," he says of the Loudoun County Bluegrass Association members downstairs, but "in my days, you played dance music."

Every Tuesday since January, local musicians have come to the assisted living community to practice together, have some fun and entertain the residents and the odd stopper-by. Few of them are professionals and their abilities vary, but they share a love for "picking."

The Loudoun County Bluegrass Association is the brainchild of Randy Collins, president of the Loudoun County Chamber of Commerce. It was born during one of the chamber's monthly mixers, when Collins was talking with Morningside administrator Julie Franklin and the conversation drifted to their mutual love of the music. He wanted a place to practice with other musicians, and she wanted entertainment for the residents. It was a match made in bluegrass heaven.

"Bluegrass is very popular in the D.C. area. My goal . . . was to provide a place for what I call 'closet musicians' to play," says Collins, 38, who moved to Loudoun in 1995 from Front Royal, Va., where he fine-tuned his skills in a weekly jam session. Given Loudoun's agricultural heritage, he was amazed to find that there were no such jam sessions here--so he started his own.

"This is a contact sport," he says. "You can't learn this by yourself."

Bluegrass is an outgrowth of country music that originated in the 1940s. With its emphasis on acoustic--unelectrified-- instruments such as the banjo, mandolin, bass, fiddle and guitar, it was seen as a way to keep country true to its roots. Championed by the legendary Bill Monroe, the style developed into a genre all its own with distinctive high-paced tempos, close harmonies and complex instrumental displays. Bluegrass got a boost during the early '60s with a mass popularization of folk music that continues today, both as a traditional branch of country music and a progressive one called New Grass.

As musicians begin to drop in, Collins slaps each one on the back. "How you doing there, brother?" he asks, whether he knows them or not. Soon they are ready to play, practice and learn.

Winnie Lare, 72, loves bluegrass night. A retired hairdresser who used to own the Colonial Salon in Loudoun, she has been at Morningside for four years. The jam session, she says, "gives us a chance to stretch the body and kick the heels." Lare raises cockatiels in her room and is quick with a witty retort. She is not unusual among Morningside residents; there is a quiet energy among them, a love of life.

Evidently, the residents are learning about the music right along with the musicians. "One keeps asking for a Frank Sinatra song," Collins says, chuckling. He hopes to teach his audience that "acoustic music has a life of its own."

The musicians are sitting in a circle. Their numbers vary through the evening, as does their individual ability to keep up--but they never stop beaming. At one point, there are three guitars, three banjos, a dobro, a fiddle and an electric bass. The sound is a little mushy, but nobody seems to mind. Someone hollers "Woo-hoo!" The seniors are smiling, their toes tapping.

Tim Simpkins, 27, sits at the edge of the circle with his guitar in his lap. Between songs he shouts, "Do you know 'Sweet Sally Brown'?" The group frowns. "Do you wanna learn it?" They grin again as he launches into the tune, and within one verse everybody is more or less playing along.

Simpkins, an electrical engineer, started playing classical piano at 6. He moved on to claw-hammer dulcimer at 14 and guitar at 21. He volunteered at nursing homes for 10 years starting as a teenager. He liked the idea of the Morningside jam session so much that he has been coming by on Thursday nights to play the piano.

It was on one of those Thursdays that he met Becker. The two have begun collaborating to rearrange a melody Becker wrote and copyrighted. The song will be a tribute to life at Morningside, and Becker hopes to perform it some day for his fellow residents.

Jo Ellen Carci, marketing coordinator of Morningside, is poised for a huge increase in the demand for retirement communities as the baby boomers age. She said she'd like to see more community groups and businesses take an interest in the residents, as the musicians do.

The group moves into renditions of "Wabash Cannonball" and "Earl's Breakdown," bluegrass classics. Doug Adair, a chamber member and a friend of Collins's, belts out "Glendale Train" in a solid tenor. "Learning these bluegrass songs," he says, is "like learning a culture." He, too, is surprised that with all the pickers in the area, this is the only real forum for them.

Frank Markwith, 83, has had a lot of music in his life. His father was a violinist for the New York Philharmonic, and he used to play bluegrass on a five-string guitar. He has been at Morningside for a year now and likes to listen in on the jam session every week. The music is good--although the players do too much talking for his taste.

"They're laughing," he says. "They make us feel good."

As 9 p.m. rolls around, the audience has thinned noticeably. Borge Ulland, 59, a veterinary pathologist and treasurer of the Tri-State Bluegrass Association, begins packing away his banjo and guitar. Ulland says tonight's jam was one of the best--lively and enthusiastic, with a few newcomers. He likes playing for this built-in audience that clearly appreciates the musicians' efforts, even though "we kinda outlast 'em sometimes."

They have not outlasted Ellen Gant tonight. She is among the last to leave, moving slowly with her walker--the one who "never listened to much of anything."

CAPTION: Bob McVane, left, shares a laugh with fellow musicians Borge Ulland, Randy Collins. Collins organized the Tuesday sessions at Morningside House.

CAPTION: Marcelle Leckie, a resident of Morningside House in Leesburg, claps to the rhythm of the bluegrass music.

CAPTION: Bill Jones plays guitar during bluegrass night at a Leesburg assisted living community.