Michel Petrucciani is carried onstage by his manager, who places him on the piano bench. The hands are normal but beyond the forearms his body dwindles. Halfway into his 21st year, jazz pianist Petrucciani is three feet tall, barely over 50 pounds. His bones grew without calcium to strengthen them, which means they scarcely grew and often broke--hundreds of times.

Then he starts to play, and none of that makes any difference as his fingers encircle a melody, explore its nuances, expound energies in a style that ranges between the lyrical quietude of Bill Evans and the aggressive insistence of McCoy Tyner, with touches of Thelonious Monk, Bud Powell and Keith Jarrett.

"When I play, I play with my heart and my head and my spirit," the young Frenchman says in an accent so slight one would hardly know he's only been speaking English for two years. "This doesn't have anything to do with how I look. That's how I am."

Petrucciani suffers from osteogenesis imperfecta, a rare disease also known as glass bones.

"My condition is getting better and better all the time," he says brightly. "Now the calcium is coming more and more. As I'm getting older, my bones are getting strong again. That's good. Also my arms are growing stronger."

He looks up, his face and voice younger than his manner. He sits on the edge of the couch in his hotel suite, his tiny crutches propped next to him.

"I never think about having problems," he says. "I'm here to have a good time. I like to have a good time. It's like driving a car, waiting for an accident. That's no way to drive a car. If you have an accident, you have an accident, c'est la vie. I don't think about what's happening to me. Hopefully I won't have an accident for a long time now. And that's good."

The unheralded Petrucciani was one of the major surprises this summer's Kool Jazz Festival, as much for the eloquence of his solos as the inspiration of his playing. There's no way to avoid acknowledging his condition, but he seems to have a wonderful handle on it. Having performed in the afternoon segment, he could be found zipping in and out of the various evening sessions, carried by his wife, Erlinda, or by his manager, Gabreal Franklin.

Instead of being bitter or frustrated, Petrucciani seems to transcend his problems. Ask him what's hard for him and he says "being a jazzman."

Mostly he is effervescent, with questions and observations flowing restlessly out of him. He blows out his cheeks in imitation of Dizzy Gillespie, he puts on a harsh business-like face in anticipation of upcoming record contract negotiations, he recalls a song by exuberantly scatting its melody, taking enough delight in his performance as a singer to announce: "I want to change my career, man!"

He moved to the United States two years ago, but he'd been absorbed in music his entire life.

"I was born in a jazz climate, listening to Wes Montgomery, Bill Evans, Errol Garner," says Petrucciani, whose father is a jazz guitarist. "That's what I wanted to do from the first time I played piano."

Initially, though, he went through eight years of classical training, giving it up mostly because he disliked the pretentiousness of the people in that field.

"But Chopin, Beethoven and Mozart wrote good stuff," he says. "They wrote songs that helped me out a lot. After that, though, I was jazz all the way."

He started playing in French clubs when he was 9 (on drums at first), expanding his performing radius as he got older until he became a familiar sight at European jazz festivals. He cut his first album when he was 16 and has done two others, including a duet project with saxophonist Lee Konitz. His precociousness is not only musical: two years ago, he knew no English ("well, a little bit, all the obscene words," he laughs). Now he sounds as if he'd been born in America of French parents. "I was born in France, my parents are Italian and neither speaks any English. Oh no, man, no wayyyyy!"

Petrucciano's speech is flecked with colloquialisms, the patois of the jazz musician. "It's our own, man, you can't go against that," he says.

"I didn't want to stay in France for different reasons--some personal, some musical--so I was really ready to go and live here. I checked it out and as soon as I landed in New York, I loved it, even the airport's smells. People think I'm crazy when I say that, but it's true."

Then he went to California and looked up an old friend who had dropped out of music and was working on a Big Sur estate that belonged to reclusive saxophonist Charles Lloyd. Petrucciani met Lloyd's wife, Dorothy, who "took me up to play the piano. I started playing one of her favorite tunes "I Can't Get Started" , and it . . . struck her. She picked up the phone, called Charles in Santa Barbara, held the phone up while I played."

Lloyd, complaining that it was impossible to "hear" music like that over the phone, jumped in his car and made the three-hour drive home in two.

"Charles doesn't speak any word of French and me no word of English either. But when we met each other, we laughed and had a really good time. Our eye contact was just enough . . . and the music that we shared. I don't have any problem to communicate with people, I never have. I like to share some stuff and to have people share some stuff with me, that was no problem when I came."

Lloyd had been out of the music scene for a while when he met Petrucciani.

"Charles is the kind of guy who doesn't speak too much but thinks a lot. He just said immediately 'We're going to play together.' "

Which they did, putting together a working quartet and recording an album at last year's Montreaux jazz festival. They will do a number of festivals again this summer, with Petrucciani also perfoming solo or with his new trio, which includes bassist Charlie Haden. In the next few months, there's a solo album project and, the pianist hopes, a trio record. He'll be on the road until November, after which he and his wife will move to San Francisco, to be closer to the action. "Jazz is very happening there."

In the meantime, the word is beginning to spread about this remarkable young pianist. Asked about any sense of discrimination in hiring because of his physical condition, Petrucciani thinks back hard. "So far, no. So far, so good."

He pulls himself up on the edge of the couch. "People should try to go further and further in whatever they do and that's what I'm trying to do myself. I try to grow all the time, for the people and for myself."

He looks at his hands. "I play piano, I'm happy the way it worked. I'm happy the way I am."