Saturday night at the Warner Theater, a bona fide virtuoso will be offering a self titled "Intimate Evening." Pianist Keith Jarrett returns to the Washington area (he played a solo recital at the Carter Barron Amphitheater this past summer) with his new quartet and enough music to fill up a two-week stand. There is no question that Jarrett is a talented musician, with a fertile mind and the technique to bring his ideas to fruition. Still, the uninitiated should be aware of several things.

For one, some Jarrett music can be difficult to fathom, especially the esoteric "Hymns/Spheres" cycle (probably none of which will be heard Saturday, since it was written to be performed on church organ) and some of the more intricate compositions for quartet.

It remains to be heard how Jarrett will respond to his new supporting players (Jan Gabarek, Palle Danielsson and Jon Christensen) though he is no stranger to European musicians, having worked extensively with Gabarek on Jarrett's ECM releases.

Neither of his most recent albums - "Bya-blue" (ABC AS-9331) and "The Survivors' Suite" (ECM-1-1085) - offers any clues because both were recorded with Jarrett's old quartet: saxophonist Dewey Redmen, bassist Charlie Haden and Paul Motian on drums. That trio previously backed Ornette Coleman during his experimental days, and never failed to offer adventurous, if sometimes inaccessible, instrumental backing and compositional prowess.

The new Jarrett releases appeared within a week of each other, not the most advantageous marketing technique but necessary because "Byablue" marks the end of Jarrett's affiliation with ABC Records while "The Survivors' Suite" starts his quartet work with ECM, for whom he has recorded many solo pieces and other group projects in the past. It also signals the end of his working with Redmen, Haden and Motian. Apparently, both companies decided to ship their new material for the holidays and forget about possible competition.

Strangely, "Byablue" is the easier listening. Strange because Jarrett's ABC quartet work has usually been his outlet for ensemble experimentation. Here, though, "Rainbow" and "Trieste" are particularly lyrical examples of his keyboard abilities.

"The Survivors' Suite" also contains some brilliantly melodic passages but, since it is structured as one continuous piece, the passages are fewer and farther between. Both records, though, prove that, despite a prodigious outpouring of product, Jarrett remains consistently inventive.

Ironically, the only threat to Saturday's "intimacy" may be the star himself. Not that Jarrett's music does not lend itself to such a warm term: He has almost single-handedly created the genre of "chamber jazz" whih is quiet yet forceful and often touches the innermost chords of the mind and heart. Jarrett the man, though, can often be another story.

He has been known to lecture audiences on the etiquette of concert-going and has chastised critics, photographers and others of "that ilk" for both real and imagined slights. Sometimes he speaks to his fans like a camp counselor berating a group of eight-year-olds, and this can drain the wonder of an otherwise magnificent performance.

Eccentricity is the price one often pays for genius, and Jarrett certainly rates that accolade, which is tossed about awfully loosely of late. Any time Jarrett plays, expectations are high and the results usually exceed them. Few artists can truthfully make that-claim.