After three shows over the course of three days this weekend, concertgoers who''ve never heard the celebrated guitarist Bill Frisell are likely to come away with three distinct theories about who he is: 1) a virtuoso experimentalist; 2) a Thelonious Monkish composer; or 3) a jazz-folkie.

Yes, yes and yes. As the smart luckies with full-festival tickets will see, Bill Frisell is a three-headed monster. A frighteningly talented monster, but a nice one.

The Friday night crowd, who will hear him perform with a quartet featuring L.A. steel-pedal session man Greg Leisz, bassist David Piltch and drummer Kenny Wollesen, will witness a country-jazz pioneer who creates bucolic soundscapes as gently pretty as a stroll on a late-summer evening. The Saturday audience, who will see the same quartet with the addition of a superhip downtown New York horn section--including trombone god Curtis Fowlkes and trumpeter Ron Miles--will note a bandleader and composer whose lyrical, intricate works tell profound musical truths. And folks who catch Sunday''s set, a duo with the legendary drummer Paul Motian, will behold a singular, virtuostic guitar player who seamlessly melts chunks of disparate musical genres into an exquisite sound all his own.

Over these three days, Frisell will demonstrate an unassuming mastery of the vast range of American music that is almost too big to be called simply jazz, even as he stretches the boundaries that define that word. Mostly, Bill Frisell uses his prodigious talents to play deceptively simple, stunningly pretty songs. His own compositions (which make up most of his live sets, though he has covered everyone from Monk to Bacharach) remind us that jazz, or music itself, can be adventurous and challenging and provocative and very beautiful at once. But while those who insist on a steady diet of pyrotechnical bombast should be warned that Bill Frisell is likely to softly shatter their preconceptions, fans of easy-listening jazz had better gird their minds for blowing too.

Frisell, after all, spent years wielding his ax as a member of John Zorn''s Naked City ensemble, furthering the avant-garde''s assault on the postmodern frontier. Their self-conscious dissection of the idea of jazz, a precise, often jarring cut-and-paste pastiche, sounded at times like a hyperkinetic cartoon soundtrack and at others like a punk-jazz affront. And although it''s true that before and since, on scores of albums with a half-dozen bands, Frisell has veered hard in another direction--toward the straightforward and pretty--he will still, in the midst of a gorgeous moment, kick his effects box and launch the music into a psychedelia that''s more Miles than Monk, more Jerry Garcia than Wes Montgomery. And then, like the Dead, in a moment he''ll return to the Americana that is his musical homeland.

Over the past year or so, the steel-pedal player Greg Leisz--a studio journeyman who has backed the likes of Jimmie Dale Gilmore and Joni Mitchell--has been Frisell''s most frequent collaborator on these backroad journeys. A back-to-back pair of songs on Good Dog, Happy Man (1999) offers an example of some of the things MJF audiences can look forward to this weekend.

"Cold, Cold Ground" makes its point immediately, featuring a four-bar melody so simple it''s almost more like a phrase, played in loose tandem by Frisell and Leisz. The melancholy phrase is repeated again and again until the band introduces the simplest blues riff imaginable, built around one chord and a throbbing four-four beat repeated bar after bar, relentlessly, almost painfully so, before the players return to the lilting, stripped-down melody. Eventually--more than six minutes into the nine-minute song--the pedal-steel seeps in for a solo, then swells and lifts off, soaring for a moment that stretches out into a couple of sweet, sublime minutes, and then it''s over.

This piece of hardcore folk-blues minimalism is followed by "That Was Then," another exercise in forthright country-jazz fusion put to the service of brainy hedonism. The song takes its time about declaring its intentions, teasing around the melody just long enough to create a pleasurable sense of anticipation, if you catch my drift, until Leisz and Frisell lock horns (or strings) to make the melody-and-harmony thing happen, which again is more like a riff in its utter simplicity; they repeat it immediately again, and again and again, hewing always close to the raw melody. It''s as though the theme is too pretty for the players to abandon for even a moment''s indulgence in a commonplace variation or jam.

Not even the studly horn section distracts Frisell from his unyielding commitment. On several albums with these guys, the repetition is a theme, the simplicity is a theme, the urgent prettiness itself is a theme, an idea, a metaphor. We can call what he does "jazz," but this isn''t about jazz, or about music either; Frisell''s music is about some ineffable place that sometimes only jazz can get us to. By stripping the music to its essence, he makes that stuff clear.

Simplifying even further in Sunday''s set of duets with Paul Motian, Frisell will return to his deepest roots. Motian, who started out playing with Monk himself, gave Frisell his first full-time gig as a sideman 20 years ago, and the pair have made a dozen albums together since. It''s certain that Sunday''s show will be influenced by the festive atmosphere of the festival, and therefore almost anything might happen. For serious Frisell fans (whose ranks are likely to have swelled over the prior 48 hours), this will be an opportunity to get a straight dose.

The man can make his guitar do anything, but it''s always easy to identify him after a couple of licks. His signature sound has a supple, sneaky attack, as though he were playing the steel-pedal himself, or as though he were blowing the guitar rather than picking it. Even before he started hanging in Nashville (figuratively speaking), he could get pretty twangy for a one-time New York hipster (he moved to Seattle a decade ago), and he will surprise you suddenly with something familiar, kind of echoey and trippy that sounds like (aha!) surf music.

He can also make his instrument appear to turn inside-out, vault into the sky and explode, but he does so with reserve. All of this virtuosity and range seem guileless. There is nothing show-offy about Frisell''s brilliance. He has something he wants badly for us to hear and feel, and he is willing to do whatever it takes to make us feel it. A Whitmanesque hero who''s mastered America''s musical gift to the world, Bill Frisell contains multitudes. And this weekend, we''ll get a rare chance to experience a lot of them.