As he leans back on the small white couch in Blues Alley's closet-sized dressing room, John McLaughlin looks surprisingly fit for a 45-year-old veteran of jazz nightclubs. His hair is graying, but his square-jawed face is tanned and, wearing a dark blue polo shirt, he looks more like an Annapolis lawyer than the British jazz guitarist and disciple of eastern mysticism he has been.

As soon as he begins to talk, however, it's clear that jazz and mysticism are not only foremost in his mind but inextricably linked. At the very first question, he throws his hands in the air and says with a world-weary sigh, "Why! Why! Everyone always wants to know why. The music just is; we accept it without having to put it into words."

In 1970, McLaughlin played on Miles Davis' "Bitches Brew," the breakthrough jazz-rock fusion album. As the electric guitarist, he had the crucial role of linking the big metallic sound of rock with the improvisational flexibility of jazz. He did this so well that Davis titled one composition for the album "John McLaughlin" and used the guitarist on three other records.

That same year, McLaughlin also became a disciple of Sri Chimnoy, the Indian spiritual teacher. The Yorkshire native was fascinated by the concept that religion and music are inseparable and began to explore both pastoral European music and traditional Indian music on the acoustic guitar.

Today McLaughlin says he admires both Davis and Chimnoy but is no longer a disciple of either. Nonetheless, those two mentors still influence his work. He continues to explore the more aggressive side of his personality with the electric guitar and the gentler side with an acoustic model. McLaughlin no longer wears the severe white clothes of the true believer, but he uses the vocabulary of a mystic.

"We are slaves to the music," he says. "I am a slave to the guitar. I'm an adoring slave, though sometimes I hate it, too. Music is a very demanding master, because it insists on the truth. There's no place to hide in music, because it is so obvious when a musician is lying."

McLaughlin is best known for his leadership of the Mahavishnu Orchestra, the early '70s electric fusion band that yielded such subsequent stars as Jean-Luc Ponty, Jan Hammer and Billy Cobham. When the group disbanded in 1975, he turned to the acoustic guitar and formed the European-Asian quartet known as Shakti.

His switches continued: the electric guitar for the short-lived One Truth Band in 1979 and then back to the acoustic as part of a touring trio with American guitarist Al Di Meola and Spanish guitarist Paco De Lucia in 1981-83. In 1984 he took on the guitar-synthesizer in a resurrected version of the Mahavishnu Orchestra.

"I can't tell you why I go in a particular direction at a particular time," McLaughlin says. "Generally speaking, it's the music that calls the shots all the time. When I have an impetus within me to go in a specific direction, I have to follow it." How does someone know just what the music is telling him? "You just reflect on it and work on it," he advises, "and it will make itself known. Music never lies to me. People in general would be better off if they trusted their instincts."

During his current stand at Blues Alley, which continues tonight and tomorrow, McLaughlin is playing a nylon-stringed acoustic guitar, and is joined by Jonas Hellborg, the young Swedish electric bassist from the latest Mahavishnu Orchestra. The duo thus balances the opposing tendencies toward electric and acoustic instruments that have marked McLaughlin's whole career.

"Because the acoustic guitar is such an old instrument, such an antique, it evokes something very ancient in the human imagination," he suggests. "It has the characteristic of a kind of pathos that the electric guitar doesn't have.

"With an electric guitar, you can go 'vro-o-o-m,' " he says with an illustrative windmill swing of the arm as if he were hitting a full chord. "With the acoustic guitar, you go 'plink' and the note is gone. It's born and it dies, and there's nothing I can do about it. But for that brief moment, it comes out of nothing and then goes back into nothing. It gives the acoustic guitar, especially the nylon-stringed guitar, a certain poignancy.

"On the other hand," he continues, warming to the subject, "the electric guitar note hangs in the air and creates its own atmosphere. While that first note is singing, you can play other notes and create a dialogue that way."

If McLaughlin's discussion of music reflects his years of immersion into eastern philosophy, his performance reflects the irreverence of Miles Davis. Seated before Blues Alley's exposed brick backdrop, McLaughlin throws out short, angular riffs that Hellborg digests and returns with a twist. Much as Davis does on the bandstand, McLaughlin tosses out another figure and then another until he has established a musical landscape of streamlined phrases and empty spaces.

"For a musician to work with Miles is a wonderful experience," McLaughlin insists. "It's like a painter working with Picasso. What you learn from Miles is so conceptual; you learn what to play in a certain situation and what not to play. When you work with Miles, though, you have to realize that when you give him an idea, he will turn it all around. It will work perfectly in his way, but it won't necessarily be your way.

"The best example I can think of is when we recorded Joe Zawinul's tune, 'In a Silent Way.' It had a lot of chord changes and we had run through it a couple times, but he {Davis} didn't like it at all. He told me, 'Play it like you don't know how to play the guitar.' So I played it all in E major, just one chord. When he played it back, I couldn't believe it; he had taken Zawinul's complex tune and turned it into something simple and beautiful. I just stood there with my mouth hanging open in the studio."