BECAUSE OF an accident, because some hard-pressed musicians didn't want to lose a regular job, because something clicked 25 years ago to the night, Washington became the bluegrass capital of the world. And the Country Gentleman became its urban gentry.

Kentucky's Bill Monroe may have fathered bluegrass out of traditional string band music, and he may have joined Flatt and Scruggs and the Stanley Brothers in helping it achieve mass popularity, but as ex-Gent Eddie Adcock says: "The bluegrass music that people listen to today came from the rolling hills of Washington, D.C."

Charlie Waller, the group's gifted guitarist and singer--the one constant Gentleman over that quarter-century, the irreplaceable rib, the cornerstone--shakes his head. "I know how long 25 years has to be, but it doesn't seem it to me. I enjoy the music so much that I'm lucky to be able to make a good living, even though it's still tough traveling the road."

The road. It's something the Gentlemen hit with the regularity of waves at high tide, a place where sometimes it takes a minute coming out of interrupted sleep to remember the name of your 18-year-old son. The famous bluegrass tenet "Don't give up your day job" has been eroded after 200 nights a year on the road, but Bill Yates, who's been playing Gentlemen bass for 12 years, still uses old skills as a mechanic to keep the band's massive Silver Eagle bus running. Home on the road, home on the bus, home again, home again soon.

On Monday night, the four current Gentlemen--Waller, Yates, banjo player Dick Smith, mandolinist Jimmy Gaudreau--are home to celebrate 25 years of bluegrass innovation with a concert at Wolf Trap. They'll be joined on stage by a dozen former Gents, chronologically recreating the progressive blend of style, material and humor that made the Gentlemen the most influential bluegrass band since Bill Monroe. WASHINGTON in the mid-'50s was an almost-haven for country music, and for bluegrass in particular. There were no rock 'n' roll clubs, no discos, no singles bars. Still, the music was hardly a living, more like some extra money to supplement the day job. Waller, a brash 22 year old, born in Texas, raised in Louisiana and polished in Washington, had been playing between here and Baltimore, with Earl Taylor, Buzz Busby's Bayou Boys, a dozen other forgotten bands. They sang the songs of the Osborne Brothers, Bill Monroe, Don Reno, Jim and Jesse and the other top groups; that's what was expected, that's what was known.

The Busby band, featuring banjo player Bill Emerson and guitarist Eddie Adcock, had a regular gig at the Admiral Room at Bailey's Crossroads when several members of the band were involved in a late-night car accident. Busby was seriously injured--actually, he was declared dead on the scene, but showed slight signs of life at the hospital. Adcock was also hospitalized. Emerson (who left in 1958, returned in 1970, left again in 1972 after being shot in the arm outside a club) was actually the man who convened what would become a society of Gentlemen on the night of July 4, 1957.

"In order to keep the job going for Buzz, I asked John Duffey who had grown up a mile away and been a friend for several years if he would fill in on mandolin, and he called Waller , who came down to help. We played there till Buzz got out of the hospital and the whole thing worked so well that we thought, 'Let's do something on our own.' " Which Duffey, Emerson, Waller and bassist Larry Leahy did, landing an early-morning show on WARL, starting to play the circuit. The group's repertoire was still mostly standards, but the combination of voices was already unique: Waller's biggest influence had been country music, and his distinctive tenor sounded like a young rugged cross between Hank Snow and Mac Wiseman; Duffey, whose father had been an opera star, was classically trained, which helped his rich, high tenor soar even further.

In 1959, eight bass and four banjo players later, the last vocal and instrumental ingredient joined up in the person of Eddie Adcock. Only 20, Adcock had been playing in bluegrass bands professionally since he was 16 (including a pre-Gent stint with Bill Monroe's Bluegrass Boys). He brought a distinctive and original banjo style (closer to guitar picking, in some ways) to augment Duffey's jazzy mandolin runs. And Adcock's vivid baritone was the breathy elixir that, when joined with Waller's beautifully enunciated leads and Duffey's aggressive tenor, created a spectacular harmony that had never been heard in bluegrass. The music itself was slick, a decided contrast to the raw hillbilly sound usually associated with bluegrass. But it was still straight-ahead. And what the public heard, it liked.

The Gents were still scraping in the late '50s, not unlike a Broadway show testing itself on the road. Things started getting better when they changed the basic book. Duffey started hunting up folk songs in the deepest reaches of the Library of Congress. Doyle Lawson, who replaced Duffey on mandolin in 1969, points out that it was the Gentlemen who "broke the mold of what was considered bluegrass by selecting material that was not bluegrass in the least. They were listening to people like Bob Dylan and Joan Baez. And Adcock had his Merle Travis style of banjo, so they used that a lot. A lot of things came together. They were the trailblazers, the fathers of modern bluegrass."

Coincidentally, the folk-boom of the early '60s hit its stride; with the Gentlemen doing songs like "Copper Kettle," "Long Black Veil" and "Handsome Molly," they achieved an immediate rapport. "We may have offended some of the diehards," Waller admits, "but basically we did tasteful stuff, and me being really more of a country singer added another flavor to bluegrass. We made an awful lot of people come over. If they heard us play 'Greensleeves,' they'd listen more carefully and decide we was pretty good and become a fan."

As their repertoire expanded to include such unlikely tunes as Belafonte's "Banana Boat Song," the "Exodus" theme, the Beatles' "Yesterday" and jazz tunes like "Bye Bye Blues," the Gents' shows began to sneak into new venues: colleges and concert halls (they shared the Carnegie Hall stage with Pete Seeger). "One of the things I liked best was when we went to one college and saw all these kids going up and down the street with a guitar or banjo. A boy said to me the next morning, 'I really enjoyed you fellows' concert last night.' I'd never heard it called 'concert' before. It was such a nice thing to have people really listen to what you were doing after playing so many years for noisy barroom audiences."

And where most bluegrass bands played their music deadpan, the Country Gentlemen were having a ball on stage. They'd crack jokes and crack each other up, get into slapstick one-upmanship and parody their own influence. "Cripple Creek," with its lightning runs, was a standard that young instrumentalists used to learn by slowing it down to 16 rpm on their record players; that's the way the Gents played it, right down to slurred harmony vocals that sounded like three drunk coon dogs. "It was just a natural thing, never planned," Waller chuckles. "If you have fun with what you're doing, let it be shown."

Times got better, but they didn't necessarily get good. The Gents spent 12 straight years playing at the Shamrock in Georgetown, touring on weekends. The money was never as easy as on the pop side; one of the band's 50 albums was recorded in a basement, two-track studio whose engineer kept his family shivering. "When the furnace kicked on, it made enough noise so we couldn't continue," Waller recalls. "We had to stop and wait until it went off, so he just turned the damn thing off till we got finished. It wasn't the greatest studio, but we got a pretty good sound there; in those days we cut costs any way we could." The name of the album: "The Award-Winning Country Gentlemen."

Festivals--the very first one took place in Fincastle, Va., in 1965--gave bluegrass, and the Gents, another desperately needed boost. "Before festivals, there were only Sunday afternoons at parks," Waller recalls. "But festivals came in big and helped an awful lot of musicians make a living. It wouldn't be anything at all to see Bill Monroe walk up late at night and get into a pickin' session around a fire; that's one of the things that made festivals go, a real friendly, freedom type thing. Of course, it used to be we would work one festival for three days; now there's so many of them we work three festivals in one day. But I love that part, going out after finishing playing on stage. I can let my hair down and walk around and listen to the groups. One of the things that always turned me on was hearing someone copying us. There's an awful lot of that, we're a very copied group, and that is the highest form of flattery--unless they get on stage before you do and do your stuff."

Since the band is an institution, it's appropriate that it has its distinguished alumni. Whenever someone dropped out, someone else was ready to drop in. Duffey, whom many saw as the driving artistic force in the group, retired in 1969 to concentrate on instrument repair. Two years later, with Mike Auldridge, Ben Eldridge, John Starling and another ex-Gent, bassist Tom Gray, he formed the Seldom Scene, which has equaled, and possibly surpassed, the Gents in impact and popularity.

Eddie Adcock formed an experimental bluegrass band called II Generation; Gaudreau left to join him before starting his own bands, Country Store and Spectrum; last October, he came back. Emerson went into the Navy to develop their country-bluegrass band, Country Current. Doyle Lawson left in 1979 to form Quicksilver. Ricky Skaggs and Jerry Douglas, '70s recruits, eventually graduated to their own band, Boone Creek; Skaggs, now on his own, walked off with most of this year's New Country Star awards. Gray, Adcock, Douglas, Emerson, Duffey and Lawson will all participate in tomorrow's reunion concert, along with Kenny Haddock, James Bailey, Bill Holden, Ed Ferris, Tom Morgan and Pete Kuykendall, one-time banjo player who went on to found the music's monthly bible, Bluegrass Unlimited.

There have been other Country Gentlemen reunions (practically any time the Gents and the Scene are on the same bill) and there's always a lot of sitting in. "We're all still good friends," Waller insists. "Nobody's ever had any fallouts. With so many of the earlier groups, like Flatt and Scruggs and the Monroes, they definitely did not get along later. Maybe it was the earlier generation, but we always got along good and it's genuine, it's real."

So the Country Gentlemen have survived and prospered, with Charlie Waller at the heart. Without him, everyone agrees, there could be, would be, no group. Yet that's also part of the reason there has been so much turnover. What was progressive two decades ago, or even in the group's best years, the late '60s and early '70s, has not been as compelling in the last five or six years. "We are not looking to bite off any more style," Waller said seven years ago. He calls the shots and at this point, he sees no advantage in changing the target.

"New kids come along and want to do something different," he admits. "But I can't do anything different. Everything that I come up with seems to have the same sound and I guess that's just me. If the song doesn't fit me, I can't feel it, can't do it. We've not been out looking for any new things, we've not gone electric; so many groups keep running out on the limb and keep coming back to the thing that made them. I don't really care anything about letting down what put us where we are."