There's a delicious irony in watching the three cowboys of Riders in the Sky sip their Cokeds and milkshakes in the chain restaurant run by and named after one of their inspirations, Roy Rogers. But it's not the cookin' they commemorate, pardner, it's the old singin' round the campfire with Roy and Bob Nolan and the Sons of the Pioneers, the celebrating of a time when there was a whole lot of western in country-western music, the heyday of romantic images and harmony singing and being at home on a range that didn't have a brand name.

The Riders, who appeared at the Door last night and who perform today at the Montgomery County Fair in Gaithersburg, have not only revived a music that fell out of favor in the late '40s, but have expanded their classic repertoire with new songs firmly rooted in the tradition. "The humor, the music . . . they're so fresh," says Ranger Doug Green, a former country music writer who plunged headlong into the historic end of his field. "What we sing about is wide-open spaces, the free life of the cowboy, the open range ahead, a grand and glorious West. It's just something beautiful that people can lock into, a fantasy that's part of all of America . . . and people can ride with us for two hours."

Just then a jet drowns out his words. "Mighty bad varmints in this part of the country," Ranger Doug says, while Too Slim guesses it was a "beanhawk." The Riders have just pulled into town in a 20th-century covered wagon, an 18-foot-long Dodge Ram which was occupied by wives and girlfriends, and cluttered with suitcases and instruments, the clutter of life on the trail . . . and tiny Annie Laurie Green, "our latest little Rangerette." The only difference between old trails and new is speed and horsepower; "we live it," says Green. "We stop for beans at the old chuckwagon. We have our talking skulls and campfire and saddles and blankets. Forgot the tumbleweed."

"Actually some vandals beat it to death in Davenport, Iowa," sighs Too Slim. It was good tumbleweed, too, picked off the roadside in Utah. Well, maybe some friends will ship them some like they did once before -- in a big box, care of UPS. Delivery would be made to Nashville, where the Riders all live now ("I have a little 1 1/4 acre spread," says Too Slim proudly, with Ranger Doug adding "my rambling ranch runs about the same").

The Riders popped professionally several years ago after a wholly amateur beginning at a party. Finally having an opportunity to do the old western songs, Green called Too Slim ("he was Fred LaBour in those days") and another friend and ended up "having the time of my live. We laughed all the way through and laughed for days afterwards." Bassist Woody Paul, a man of few words who has a PhD in physics from MIT, joined after a stint with Loggins and Messina. Still laughing after all these years, the band has become extremely popular in the Southwest and on campuses across the nation. Bob Nolan of the Sons of the Pioneers wrote the liner notes for their album before dying last year; Roy Rogers, another founding member of that pioneer group, appeared with them on the Grand Ole Opry. "He seemed real happy," Green recalled. "He said 'Boy, it's just like the old days.'" Unfortunately, there are no Roy Rogers restaurants in Nashville to capitalize on that friendship.

Part of the Riders' appeal, beyond their evocation of western myth, is that they look the part: Ranger Doug in the blue bib front popularized by Gene Autry and Wild Bill Elliot, fiddler Woody Paul in the Rogers-style fancy fringe, bassist Too Slim in the bright floral shirt, all three walking steady on cowboy boots. There hasn't been this much style -- such a far cry from 1981 cowboy chic -- in the Georgetown Roy Rogers in years. The band also plays its music in the old style -- acoustic and unaffected, punctuated with yodels and whoops and frequent jokes.

There's an irony in that their image is less a reflection of the real West than of Hollywood. Green concedes that "most of it developed out of the movies of the '30s," also a source for songs (along with old radio transcriptions and 78s). It's an almost absurdly romantic image that dates to Buffalo Bill's Wild West shows in the 1880s, dime novels and B-movies, but "a lot of people are glad to remember it. We wanted to take that tradition and build on it with our own material. But the spirit behind the music is something we all feel strongly about."

Having hunkered down for a spell, the Riders get ready to mosey on down to Trailways to pick up a box of T-shirts (hey, it's 1981, pardner). They unhitch the wagon from the illegal parking place, load up with family and friends and saunter out through the traffic. There's a sudden western breeze. The campfires keep burning inside Roy Rogers. Say, who was that singing "Happy Trails To You?"