Very few people at yesterday's Kool Jazz Festival saw the solo piano concert by Michael Petrucciani. Compared to the more familiar jazz figures performing in every nook and cranny of the Kennedy Center, he was thoroughly unknown, so it was little wonder that fewer than 75 people were in the Terrace Theater when Petrucciani was carried in and gently placed on a piano bench.

At age 20, Michael Petrucciani is not yet a name, but he's already a story, as exhilarating and inspiring as any soaring free-flight solo blown or plunked or hammered out during the Center's long day of jazz. By day's end, 14,000 jazz fans had turned out for the festival, which was kicked off by Ella Fitzgerald's concert on Saturday night.

Petrucciani is 3 feet tall and weighs 50 pounds; he connects to the piano's sustaining pedal with a special foot attachment. His condition, osteogenesis imperfecta (what some call "glass bones" because the absence of calcium not only inhibits growth but makes the bones extremely brittle), does not extend to his hands, and those hands burned and caressed the keyboard with a remarkable fervor.

Petrucciani's percussively edged set provided a summary of the entire Kool Festival: the music was dense, spare, driven, reflective, ornate, lyrical and dissonant. Several well-known and promising performers did little to advance their reputations, but for the most part, performances were skillfull, inventive and celebratory. For only the second time in its history, the whole center was devoted to one single event, one single genre of music. Several of the theaters provided inspiring backgrounds for the musicians. When the Art Ensemble of Chicago sauntered into the Eisenhower's high-ceilinged but slightly down-at-the-heels "Room Service" set, they immediately turned it into an hour-long rent party; at times, walls of casual percussion suggested radiators gone awry, while at other times the insistent cacophony of saxophones and trumpets hinted at traffic on its way to an after-hours jam.

In painted faces and vivid costumes, the five members of the Art Ensemble looked like hep "Cats," but a child-like pleasure in invented sound is just one ingredient of their brilliant collective improvisation. Coasting through the history of Afro-American music and culture, from field hollers, bugle calls and funeral marches to be-bop, free playing and beyond, their seamless performance ranged from a whisper to a scream and featured ideas as original as some of their 25 instruments (a plastic hose, and a Perrier bottle). The array of instruments allowed for engrossing textures, while the humor and energy seemed half circus, half theater. It was wonderful.

Later, when the sequin-resplendant Sun Ra marched his Arkestra in to the same set, he proved to be no stranger to the slapstick spirit that inspired the Marx Brothers years ago. Down the hall at the Opera House, the tenement set for "Porgy and Bess" was a marvelous backdrop for blues singer Big Joe Turner and trumpeter Clark Terry and his Jolly Giants. The 72-year-old Turner is the last of the classic shouters and his cavernous voice is as basic as the blues itself. Seated on a chair, Turner acted as if it was suddenly midnight and musky, a midland fish fry. He pumped out his lyrics, frequently centered on "pretty mamas" and "big brass beds," with the urgency of a 30 year old, his warm but masculine voice a boil of slurs, mumbles and trumpet-like blasts. Terry and saxophonist Billy Mitchell provided Turner with some classic backing riffs, with Terry also contributing a bright muted solo at one point.

Out on the Kennedy Center's blindingly white marble patio, the music was hot enough to fry an egg. Dorothy Donegan, the ecstatic pianist who was rediscovered last year, was anticipated by the crowd this time around. Her powerful attack provided jackhammer counterpoint to music that ranged from Rachmaninoff to "Cathouse Boogie" to interpolations on "Battle Hymn of the Republic."

Washington's Buck Creek Band, staunch Dixieland traditionalists, swung in style, while Panama Francis and the Savoy Sultans, a band full of legends, had a bit of a cutting contest with National Airport. Nearly every time a solo took off, so would a jet, but between flights, the Sultans managed to get the audience to tap their feet and sway their bodies with the kind of swing that did mean a thing.

And there were more highlights: Bob Wilber and the Bechet Legacy recreating "Down in Honky Tonk Town" and other sounds that emerged from low-ceilinged clubs on 52nd Street when Bechet worked there in the '40s; Jack DeJohnette's Special Edition sliding into an exuberant tune called "Festival" that was more Brazilian carnival and New Orleans Mardi Gras; pianist Oscar Peterson, whose blinding technique sometimes softened to merely frothy invention (at one point, he slipped from tireless stride to a one-note Basie ending that was as concise as it was uncharacteristic); Horace Silver pacing a quintet that couldn't even have been in diapers when he first established himself as a jazz force.

The major disappointment was VSOP II, the Herbie Hancock Quintet featuring young trumpet sensation Wynton Marsalis. VSOP II seemed unable to come to terms with the sound system at the Concert Hall; the group blasted away and the resulting muddy mix displaced the individual character of the players. Marsalis seemed distracted and blew hard but not brilliantly, while the group as a whole seemed content with rehashing their recorded efforts.

Similarly, the Festival Allstars, with Freddie Hubbard in charge, never seemed to jell, a case of disparate styles remaining disparate. Another marvelous trumpet player, the perennial pleaser and class-of-one, Dizzy Gillespie, teamed with young Jon Faddis and the apparently eternal Art Blakey for a pile-driving set of straight-ahead jazz that made the Opera House the hottest seat of the day. Fans were able to squeeze in only as other fans squeezed out; there was hardly room for Gillespie's bullfrog cheeks.

While Spyro Gyra, the festival's one concession to pop-jazz fusion, was crowd-pleasing but thoroughly unsurprising, guitarist George Benson made a powerful return to his jazz roots in a vocal-less set with saxophonist Stanley Turrentine and organist Jimmy Smith. All three are veterans of the funk and finesse lounge combos so prevalent in the '60s and in churning through some familiar material, they seemed to be having a fine old time.

The festival was a celebration of solo genius and group empathy: for every searing statement by a soloist, there were bright and brassy ensemble passages and a whole lot of Ellingtonia, appropriate for the Duke's birthplace. Archie Shepp paid homage to another Washington jazz figure, the late Sonny Stitt, with a transcendent "The Good Life," while the music of Thelonious Monk, Tadd Dameron and Sidney Bechet was revived and extended in performances by Sphere, Dameronia and the Bechet Legacy. The Modern Jazz Quartet, founder and definer of chamber jazz, celebrated themselves by reuniting and confirming the subtle grace and beauty of their style of jazz. Always, the past informed the present, even as it pointed the way to future musics.

A major failing (for the second year) is Kool's handling of local talent. With the exception of the outstanding singer Etta Jones, who was given a spot in the Terrace Theater, most of Washington's jazz figures (who had only been hired a week ago and were therefore totally absent from advertising, promotion and, apparently, consideration) were secluded in the hard-to-find Theater Lab, one of the festival's best-kept secrets. They performed gamely, relying on friends and passers-by hooked by a sound (as when The Saxes for Lester, four-strong, evoked Jazz at the Philharmonic energy, unison chases peeling off into a series of hot solos like towels at a sauna). Some locals received exposure on the terrace, while a number of pianists were misplaced in the hallway, glorified cocktail lounge entertainers. They all deserved better.

By not having music in the center's hallways as it did last year, the festival avoided the congestion that sometimes made getting to distant halls a problem. There's still something disconcerting about the wholesale audience shifting that goes on in the midst of brilliant performances. It compounds the standard problems of late arrivals and early departures, and while the clambering is good- natured and derived from curiosity rather than boredom, it still disturbs one's attention.

Nevertheless, the sheer wealth of talent outweighs the problems (without excusing them). Sometimes it's hard to make a choice, and future festivals might do well to stagger the show times, or even spread them over several nights at several different locations. Even without the in-house travel, 10 hours of uncompromising music is a bit much even for the jazz buff. It's almost too much of a good thing.