CLARENCE "Gatemouth" Brown's only nationwide hit, way back in 1949, was titled "My Time Is Expensive."

These days, his time is precious: Earlier this year, after a routine exam, Brown was diagnosed with lung cancer. At age 80, and already burdened with a heart condition, Brown was later deemed by doctors to not be a candidate for surgery.

By then, he'd already decided to forgo any treatment and simply continue touring as long as his health allows.

Calling from his longtime home on the shore of Louisiana's Lake Pontchartrain, the unrepentant pipe smoker -- "well, I'm slowing down on that some," he says sourly -- espouses a certain distrust of the medical profession.

"I can see right through the plot of doctors," Brown says. "Not that all doctors are bad, I can't say that, but it seems like they want a lot of money, and the first thing they want to do is cut you up and see if you do have anything like that [cancer], when it's a known fact that when air hits it, that's it."

Just don't go thinking this is it for Gatemouth Brown, that Friday's performance at the Barns of Wolf Trap is one final opportunity to appreciate his perpetually joyful celebration of American roots music.

This is not the last time, he insists.

"No, that's right!"

Still, there's a certain eeriness to the first words Brown sings on his brand-new album, "Timeless."

"Goodbye I hate to leave you now, goodbye / I pray that I return to you someday / You pray that it shall be just that way / So long for now." The song is titled "For Now So Long."

Except "I wrote that years ago," scoffs Brown.

More than 50 years ago, in fact. You can find the first version on "The Original Peacock Recordings," issued by Rounder in 1990, or hear the new one on "Timeless."

If you look for those CDs in any well-stocked record store, you'll probably find them filed under blues, which is a starting point, perhaps, but a longtime straitjacket for this multi-instrumentalist (Brown mostly plays electric guitar and fiddle these days) and master of multiple genres. Though he can play blues with the best of that brotherhood, he's generally distanced himself from the idiom, desperate to avoid its restrictions, or succumb to easy categorization.

Instead, a Gatemouth concert embraces jazz, country, swing, Cajun, R&B, jump blues and, yes, straight-ahead blues.

"I always say don't call me blues because there's more music in the world except blues. I tell 'em to use 'American music' because that's what I play," Brown explains. "I just like all kinds of music, man. I don't like to be stuck in no one market, like a lot of people -- they can't get out of the pocket. I just never wanted to be that way."

What he's been is an influence -- identifiable progeny include Johnny "Guitar" Watson, Freddie King, Albert Collins, Lonnie Brooks and Johnny Copeland -- and an inspiration. Which explains the outpouring of supportive messages from everyday fans to Brown's Web site, as well as the kindness of stars.

"A friend of mine did a great thing for me," Brown says humbly. "[Carlos] Santana sent a check for 10 grand last night!"

Santana sat in with Brown at this year's Montreux Jazz Festival and will likely guest at an upcoming San Francisco show, one of several high-profile club dates that will help defray mounting expenses. Greg Allman will do one in Atlanta, Ry Cooder another in Los Angeles. Given Brown's stature in music circles, the list is sure to grow.

Meanwhile, he's continuing on the road, as well as working on a long-planned book with Austin writer Colin Walters. And you know you want to learn the fleshed-out details of experiences that have made Brown a virtual encyclopedia of American music. That cross-pollination occurred should not be a total surprise since Brown was born in Louisiana and grew up in Texas, both fertile regions for such activity. His father was likewise versatile (playing guitar, fiddle, accordion, mandolin and banjo) and broad-minded.

"He played mostly Cajun, country and bluegrass," Brown recalls. "To me, that was a good wide range, and I imagine he took it further." The Gatemouth nickname came early -- as a child, Brown was known for his loud voice, as, apparently, was his brother James, known as "Widemouth."

In 1945, Brown began his professional career in San Antonio, as a drummer in such bands as Howard Spencer and his Gay Swingers and W.M. Benbo and his Brown Skin Models. But he'd learned guitar (and fiddle) from his father, and he finally put that to use in 1947 in a manner that has become legend. One night, Brown was in the audience at Houston's legendary Bronze Peacock club to see Texas blues guitar pioneer T-Bone Walker. During the show, Walker's ulcer acted up, and he had to leave the stage, at which point Brown stepped out of the crowd, picked up Walker's famous Gibson ES5 and improvised a boogie:

"My name is Gatemouth Brown, I just got in your town / If you don't like my style, I will not hang around / I've had a hard time, baby, trying to get a break / If I don't make it this time, it still won't be too late . . . "

Walker was not amused, but the crowd loved "Gatemouth Boogie," showering its author with an impressive $600 in tips -- a significant amount in that cash-strapped post-World War II era. Also impressed was club owner Don Robey, who soon made Brown a regular at the club and bought him his first Gibson L-5 guitar. Robey also became Brown's manager, hooking him up with a 23-piece big band that toured the South and Southwest, making Brown one of the first to front a big band with electric guitar.

And when several of Brown's 78s for the Aladdin label didn't get sufficient promotion, Robey created Peacock Records to take Brown to a national audience. With a roster that eventually included Bobby "Blue" Bland, Junior Parker, Joe Hinton and Big Mama Thornton, Peacock became the first successful postwar black-owned record label.

Brown would have a lot of regional hits, such as "Boogie Uproar," "Dirty Work at the Crossroads" and "Okie Dokie Stomp," most built around his big, riffing band. But "My Time Is Expensive" and "Mary Is Fine," both released in 1949, remain his only R&B chart hits, and he never realized much in royalties since Robey's business practices were somewhat shady, something fairly common in the independent record world at the time.

"Gate always says, 'I wouldn't be where I am now if it wouldn't have been for [Robey],' " says Jim Bateman, Brown's manager for the past 28 years. "But he'd perhaps have more royalties if Robey had been an honest businessman."

Brown stayed at Peacock until 1959, by which time his big band had been decimated by rising costs and diminished demand. In the '60s, he spent time in Nashville, sometimes singing country, sometimes leading the house band on Hoss Allen's syndicated R&B television show, "The!!! Beat." Years later, Brown would record a duets album with Roy Clark, "Makin' Music," and become a regular guest on "Hee Haw." He'd come to appreciate country growing up in Texas and "had been playing it all the time," Brown says. "There's always something new comin' in my mind that I'm gonna do, but there's nothing I've pushed for and haven't did."

In the '60s, Brown took a hiatus from music, moving to New Mexico to work as a deputy sheriff, which left him rested for the hectic '70s, when he developed a major following among Europe's developing blues audience. He toured the continent nearly a dozen times, becoming a fixture at the Montreux Jazz Festival, and recorded nine albums for European labels. Mid-decade, Brown became an ambassador for American music when the State Department sponsored a tour of Africa, China, Japan and the Soviet Union.

Stateside, Brown's recording profile improved with 1982's Grammy-winning Rounder album, "Alright Again!"; the title was taken from "I Feel Alright Again," another of those late '40s songs credited to Robey (who died in 1975). Brown has since recorded for Rounder, Alligator, Verve, Blue Thumb and now Hightone. While "Timeless" is typically all over the musical map, Brown says his next album may well be fiddle-focused.

"I don't know what it's gonna be, man. It might be something of everything, but I'm thinking I might do bluegrass."

No matter what style music he ends up with, don't expect Brown to jam. He hates it.

"It winds up being a train wreck," he says, "unless you're playing with older guys like Ernie Tubb and those people, some of the well-seasoned musicians. When they said 'jam session,' those people knew what they were doing because everybody played the right stuff. But you say 'jam' now, everybody's trying to outplay each other, and when that happens, it becomes nothing."

Not that Brown is worried about being overshadowed. "Let's put it this way, they would if they could but they can't. It's not that they don't want to. . . but they can't."

Which doesn't mean Brown won't show up as a special guest on other musicians' recorded projects. Earlier this year, he did a session with Los Super Seven, the border-music super-group that includes David Hidalgo and Cesar Rosas of Los Lobos, Ruben Ramos and country star Rick Trevino. They asked Brown to do Blind Lemon Jefferson's "See That My Grave Is Kept Clean" for their next album. Since 1928, it's been a blues classic, but the blues is probably Brown's least favorite genre. Apparently, he had no problem with the lyrics, but did change the music so he could "tolerate it."

CLARENCE "GATEMOUTH" BROWN -- Appearing Friday at the Barns of Wolf Trap. * To hear a free Sound Bite from Clarence "Gatemouth" Brown, call Post-Haste at 301-313-2200 and press 8121. (Prince William residents, call 703-690-4110.)

"I just like all kinds of music, man. I don't like to be stuck in no one market," says multi-instrumentalist Clarence "Gatemouth" Brown, 80.