As the final strains of Dmitri Shostakovich's Second Piano Concerto fill the Meyerhoff during rehearsal, concertmaster Herbert Greenberg leans toward the teen-ager at the Steinway, taps him lightly on the back with his violin bow and says, "Bravo!"

Orion Weiss, 17, nods and gives the concertmaster a huge smile, full of youthful exuberance. He seems to say, "Yes! I'm here, playing Shostakovich. Life is beautiful!"

He arrived Wednesday night, a young man in the service of his muse. At first he thought the offer was a joke: Fly to Baltimore and replace the great Andre Watts in three performances of a major work.

It made him giddy. Sure, he gave his all in every performance. This was different. This was something out of a Hollywood movie in which a personable, down-to-earth kid steps in at the last minute and saves the day.

That's how Watts, 52, started his career. In January 1963, Leonard Bernstein called Watts -- then a 16-year-old prodigy -- to replace Glenn Gould in a performance at the New York Philharmonic. With only two days of preparation, Watts took the stage and made history.

Now, it is Orion's turn.

Back home in Ohio, where he is enrolled in the Cleveland Institute of Music's Young Artist Program, his picture is in a display case along with a notice of what has happened. The school sent him flowers.

"Everybody is pulling for him," says Eleanor Holt, director of preparatory and continuing education.

Miryam Yardumian, artistic director of the Baltimore Symphony Orchestra, says she called about a dozen artist managers in hopes of finding a replacement for Watts, who canceled Wednesday afternoon due to a family emergency.

"No one had anyone who was available and had this concerto," says Yardumian.

She found Yuri Temirkanov, the BSO's music director designate, in New York and added three more names to her list. None of those pianists could do the show on such short notice. One of them, Sergei Babayan, suggested his student. Pinchas Zukerman, artistic director of the BSO's Summer MusicFest, backed the choice, calling Orion a "phenomenal" young artist, says Yardumian.

Orion was playing a computer game when the phone rang Wednesday afternoon at his home in Lyndhurst, Ohio. His mother, Miriam, was in the room, ironing. She always seems to be around when he's on the phone, he says.

"At first I thought [Babayan] was joking. But he was, like, 'No. I'm serious,' " says Orion. "I couldn't think, and I realized it was the most wonderful opportunity to be able to do this."

He practiced for a few hours, then caught a Southwest Airlines flight, arriving in Baltimore with no entourage or handlers. His parents, Miriam and Daniel, who are doctors, stayed home with his younger brother, Abraham.

"It's scary, and it's exciting. It's unbelieveably exciting," says Orion, an 11th-grader at Hawken High School. "I had a butterfly the size of a hawk or an eagle in my heart. But it's not something I think about when I'm playing."

By Thursday morning, he was on the Meyerhoff stage, rehearsing with a great orchestra led this week by the world-renowned Jeffrey Tate, who says Orion has a musical maturity beyond his years. The experience grew more magical with each hour.

After rehearsal, he munched on an apple and took questions from Booker T. Washington Middle School students. They wanted to know if he had ever been beaten up for playing piano, if anyone had ever chased him home. His answers: No, and No.

Orion started his journey into the classical piano repertoire when he was 3 years old. For years, practicing on the family's old upright was a hateful chore. There were a million better things to do, like playing outside with friends, rough-housing with his little brother.

Only bribery kept him at the keyboard. He got a silver star for every half-hour of practice. Five silver stars added up to a gold star. Three gold stars and he would get a plastic animal. Still, there was sulking and fightingwith his mother.

"When I was 9, after a great big fight, she said, 'I'm not going to keep forcing you to practice,' " he says. "That's when I really decided I wanted to play."

Last summer, he joined Zukerman, Itzhak Perlman and others at Carnegie Hall for a performance of a Dvorak piano quintet. Last month, he played a Liszt piano concerto with the Cleveland Orchestra. Some have called him a prodigy.

"I don't listen to people saying that," he says, frowning at the overused word. "I'm a pianist, or becoming a pianist."

Now his weekdays begin at Hawken, where he takes four classes and lunches with friends. Then he is off to the Cleveland Institute of Music for piano studies. Some days he stays until late in the evening. Other times, he might leave before 6 p.m. He approaches the keyboard on his terms.

"No one makes me practice anymore. I practice when I need to," he says. "I practice because I love playing the piano."

At the keyboard, his face tells the story of Shostakovich's concerto. An intense frown comes over him during the heavy octave work; an almost prayerful serenity takes hold during the romantic middle movement. He seems at one with the music, leaning to the left and digging into the passages in the bass register. He is having a ball, enjoying the moments, losing himself in the sound of his instrument and the music rising around him.

"That's what you have to put on the pedestal," he says later, "the music, because we're working for the music."

BSO

What: Orion Weiss with the Baltimore Symphony Orchestra in a program including Shostakovich's Second Piano Concerto

Where: Meyerhoff Symphony Hall, 1212 Cathedral St.

When: 8 tonight

Tickets: $27-$60

Call: 410-783-8000 Pub Date: 3/20/99