FEW rock-and-roll artists have managed to weather the self-indulgence endemic to the pop music industry, and many have waded unashamedly into commercial compromise. But Irish blues-rocker Rory Gallagher, to borrow the title of his 1975 release on vinyl, has been going "Against the Grain" for almost his entire career.Mr. Gallagher is no journeyman guitar-basher. He brings a distinctive personal and virtuosic expression to his music by blending roots-blues elements and Celtic and zydeco sounds with driving rock and slow ballads. After a six-year hiatus - long by rock-music standards - the guitarist this spring made a brief swing through the United States, playing to packed houses. Gallagher returns later this fall to the American touring circuit with a new band. Best known in Europe and more a cult favorite on American shores, Gallagher is a pioneering blues rocker with a legendary career. In 1969, he fronted the power trio "Taste," which opened the American tour for the supergroup "Blind Faith" featuring Eric Clapton and Steve Winwood. Gallagher was on bluesman Muddy Waters's "London Sessions" and performed with such notables as Albert King, Jerry Lee Lewis, and the Rolling Stones. While many of his contemporaries - Jimi Hendrix and Clapton - immersed themselves in the psychedelic imagery of the '60s, Gallagher shied away from its excesses. "When you are touring a lot, you can take any road you like, but you won't last if you burn yourself with drugs and alcohol. Some musicians seem indestructible, but even they have to pay a price for it," said Gallagher in interviews from London, where he is currently auditioning new band members and remixing two previous albums for reissue on compact disc, and before he went on stage this spring at Boston's Paradise Club. As a solo act, Gallagher was like a Gaelic troubadour who went against the style, paint, and glitter of the early '70s, with his checked work shirt, jeans, and scruffy guitar. And unlike his peers Jeff Beck, Jimmy Page, and Clapton, commercial success eluded him - in part because of his unwillingness to release single hits, and his strict eschewal of self promotion. ve had too many opportunities to sell out," Gallagher says. "Obviously, I would like to play to bigger audiences and have a bit more success, but not if I have to commercialize. "I won't squander my credibility, whatever that is, just for one silly song," Gallagher says. "At this point, if I had a very good song that I believed in, I might consider it for radio play, but I tend to find many good rock musicians come out with very trivial songs as hits." Like many blues rockers whose careers were derailed in the 1980s, Gallagher had to contend with the era's synthetic sounds and techno-pop, which featured video dance divas and a few lip-synching frauds. Gallagher returns in the midst of a blues revival that has rejuvenated the careers of John Lee Hooker and Bonnie Raitt. This is also the year where the music recording industry was surprised by the strong sales of the Robert Johnson compact disc set, which features 50-year-old blues recordings. To Gallagher, all musical roads lead back to the 1930s and earlier. Although mindful of his Celtic heritage, Gallagher turned to those roots and country blues of the Mississippi delta for inspiration - music that he has an undisguised passion for, and sounds he discovered on radio programs while growing up in West Cork, Ireland. Gallagher says he found the "raw and rhythmic qualities," especially on acoustic guitar, to be "a deeper kind of music." The singer-songwriter, who first picked up acoustic guitar when he was nine, has made 14 solo albums, almost all of which include at least one track written by pioneers such as Sonny Boy Williamson and Big Bill Broonzy. His surprise visit to the US this spring coincided with the well-received release of "Fresh Evidence" (IRS Records) - Gallagher's first American album in almost a decade. On tour, the guitarist frequently had to explain his absence from North America. "Some of the tours we were offered in America just did not appeal to us, because it meant going around stadiums playing in front of some other huge group which had an audience not sympathetic to blues or rock-and-roll," he says. It is as a live performer that the 42-year-old Gallagher has few peers. He approaches the guitar with such passion, and critics say his improvisational journeys with the stratocaster actually go somewhere without getting lost in transit. On stage, he coaxes a whirlwind of deft harmonics and feedbacks from his open-chorded guitars in a sweat-drenched workout. In 1978, Guitar Player magazine wrote, "What Gallagher has to say about blues and rock-and-roll should be required reading for any aspiring guitarist, just as his many records and live performances should be required listening." Besides putting a new band together, the next several months will be busy for Gallagher. A film score may be in the works; the Celtic group the Chieftans have invited him to appear with them on television in Dublin; a new boxed CD set is planned; plus a world tour is in the offing. Gallagher also expects to complete several songs. And as an avid reader of mystery books and biographies, he often spices his lyrics with references to characters he finds from his books. "After writing quite a few songs now, I have not a method but a way of being patient with a couple of verses or a certain set of chords. I can match them up quicker now than I used to," he says. "The one thing you do improve is songwriting." And he has been asked by both Irish and Welsh television separately to do a video documentary on his career. "It is something I wouldn't mind doing - not for the ego's sake - but for the sake of covering 20-odd years of music," says the soft-spoken Gallagher.