ALMOST THREE years ago, on a blustery February night in Lucketts, Va., a sellout crowd jammed the Old Schoolhouse to hear the Johnson Mountain Boys, the most celebrated traditional bluegrass band of the '80s, bid their fans farewell.

After eight years of roadwork and a half dozen widely acclaimed albums, after a couple of Grammy nominations and appearances at the White House, the Grand Ole Opry and a few overseas tours, the quintet known for its western wear and hard-core music called it quits to the tunes of Bill Monroe, Don Reno, Red Smiley and other bluegrass legends. Tapes rolled that night and the subsequent recording, "At the Old Schoolhouse," went on to win a Grammy nomination as well.

Now the Maryland-based group is back, if just for the moment, appearing at the Birchmere Friday and Saturday. To hear singer, songwriter and guitarist Dudley Connell tell it, the band's occasional regrouping was probably inevitable.

"I guess our priorities had changed," says Connell, looking back on the band's breakup. "We had been playing professionally since 1980. We had all gotten married and started families and couldn't stay on the road for 150 days a year. You could say we got burned out, especially from the road work, but after we'd been away from it for a year or so, frankly we just missed performing. The interest was still there and we had the opportunity to play, so we're doing a little here and there."

In the meantime, there have been some personnel changes. Bassist Marshall Willborn and banjoist Tom Adams, who both went on to work with the Lynn Morris band, have been replaced by Earl Yager and original JMB banjo player Richard Underwood. Returning with Connell are mandolinist Dave McLaughlin and fiddler extraordinaire Eddie Stubbs, who hosts a popular bluegrass show Sunday afternoons on WAMU radio. Instead of traveling by van, the quintet now flies to its performances, which are confined to about 15 dates a year. Most are Saturday concerts or festival dates, Connell points out, which allows each member of the band to hold down a full-time job and have a family life.

"It's hard for us to get together much more often than what we're doing," says Connell, who sings lead and tenor in the group and writes songs that fit neatly alongside the band's older material. "With the coaxing of some people, we came back to do a few things and it just took off from there. But it can't take off but so much because it's hard to coordinate things. It seems that this is a happy medium."

The band's hiatus has had some unexpected benefits, according to Connell. For one thing, the time off has allowed him to concentrate more on writing.

"I feel real good about that because I went through a real dry spell," he says. "What we're trying to do now is get enough material together to record again in the spring."

In the coming months, Connell says, he hopes fans who missed the band's recent performance at Carnegie Hall will get to hear it broadcast over National Public Radio. The concert, part of a folk music series, "was one of the most exciting things {we've} ever done," he explains. "Some of the people who came to the show knew about the music, but mostly they just wanted to learn and the response was just great . . . There's not a whole lot of bands out there that do what we do, so I guess that's always been a plus."

As for other plans, Connell says 1991 is pretty much booked up -- 15 concerts. Beyond that, he says, the band's not anxious to close any doors, but it's "not opening any either. We'll just have to wait and see."