As far as most of the country is concerned, the Fabulous Thunderbirds is a Texas band. After all, the quartet, due at Merriweather Post Pavilion Friday night, is based in Austin, and its sound is flavored with the Cajun, blues and boogie traditions of the Gulf Coast.

But a quick poll of the band members finds that only one T-Bird, guitarist Jimmy Vaughan, actually comes from the Lone Star State. Two of the band members are, in fact, from Rhode Island.

Does this make it a New England blues band?

"That's where our bodies are from, but our souls are from the South," claims drummer Fran Christina. That's why he and bassist Preston Hubbard, the other Rhode Islander in the group, "always played rhythm and blues a la Freddie King and T-Bone Walker or New Orleans rock 'n' roll or swamp things, 'cause there really wasn't too much happening in the way of that music in New England."

Mind you, it wasn't as if all Texas was that much better. Vaughan recalls that he moved from his native Dallas to Austin in 1969 because "I knew when I moved down there that I could get a gig playing. They wouldn't let me play what I wanted to in Dallas.

"I'd always wanted to play with Freddie King for a little while, that kind of thing. And I wanted to play with a harmonica, do Slim Harpo and all that dirty stuff. They'd say, 'What's that?' So I said, 'Okay, I'm going to Austin.' I knew I could play at least in the hippie clubs, or something."

Vaughan actually was in a rib joint called Alexander's in 1974 when he first got a glimmer of his current band. He was playing with his younger brother, Stevie Ray, in a band called Storm, when in walked California-born singer and harmonica player Kim Wilson. Based at the time in Minnesota, Wilson was in Austin on the promise of a production deal and was being shown around the city's hot spots.

"At the time, I really didn't listen to Jimmy that much," Wilson recalls, "because I was too interested in whippin' up on the harmonica player that was there." But he did notice how well the guitarist handled a particularly tricky part on a Little Walter number -- the sort of thing that leaves no room for showing off, but that requires tremendous competence.

Wilson got up to play with the rhythm section during a break, and, he says, "the crowd loved it." He remembers shaking hands with Vaughan, but little else of the evening.

For Vaughan, though, it was an epiphany. "I heard him play, quit my band and got a band with him," he says with characteristic directness. "That's about it."

Wilson's account: "A month later, Jimmy gave me a call in Minnesota, and said, 'Hey, I'm coming up there.' So I really got to listen to him, and we started talking about the great music that was down in Texas. I decided, well, that's it. So I gave the band a month's notice, and boom! I was down there."

The rest of the lineup continued to be filled in by equally serendipitous occurrences. Christina was recommended to the band after its Texas-born drummer panicked in Boston and struck out for home. Trouble was, Christina was living on a farm in Nova Scotia with no telephone, and the T-Birds had to send the Mounties out after their man. "I looked like a lumberjack back then," Christina says, chuckling. "They said, 'Are you the drummer?' I said yeah. And we kind of looked at each other like, 'What are we getting into?' "

All along, though, it was the commonality of musical expression that made the connections stick. As Hubbard puts it, "See, we're all self-taught. We all learned from records. I think it's better. You learn by listening to the guys you love, and playing in dives."

"They can't teach you how to do this," agrees Vaughan. "That's basically what all our stuff is, stuff from here," he says, tapping his chest. "It's just how you feel."

No wonder, then, that the band has felt little need to heed the vagaries of pop taste, sticking instead to the blues and R&B basics that have sustained it for more than a decade. Which makes it all the more impressive that the group's latest album, "Tuff Enuf," is enjoying a surprising surge on the pop charts.

Not that the band is taken much aback. "It's very appealing," says Christina of the T-Bird's basic sound. "That's why it's always there. People can't help but get hooked on it. It may not be something that radio wants to play, but people still get off on it. And that's what has kept us going."

"You know," adds Vaughan, "you just keep writing songs, and your own groove gets happening after a while. To me, we're doing the same thing. It's just recorded better, and we play a lot more rock 'n' roll beats. But we still play the blues every night."