"You can perform music any way you want, as long as it's convincing," says Eugene Fodor, the only American violinist -- in fact, the only Western violinist -- to win the International Tchaikovsky Competition.

The advice was offered recently during a string master class sponsored by the Fairfax Symphony Orchestra.

Fodor, an unpretentious young man (he just turned 30 this month) and a candidate for the John-Boy Walton look-alike contest, couches most of his pointers in "this-is-only-my-opinion" terms, but a quick sift through comments at the recent master class reveals the following description of a premier violinist, Fodor-style:

He's healthy: "I think running and swimming are the best exercises for anyone. And racquetball, I play racquetball. (Pause) And scuba diving, though actually skin diving is better exercise."

His head stays welded to his violin: "My teacher (the Russian-born Jascha-Heifitz, a world-class violinist) used to get upset if I so much as glanced at anything besides the music. He never moved anything but his left hand, his right arm . . . and his eyebrows."

His eyes occasionally focus on his fingering: "Imagine what it would be like if a pianist closed his eyes and played -- it helps to focus sometimes."

His left hand rests lightly on the underside of the violin: "Don't be afraid of it."

His left fingers press the strings "as far away from the cuticle as possible. We want it on the cushion."

His right arm (his bow arm) stretches continuously, playing the tip of the bow: "The major advantage we have over Bach is that we can use more than eight inches of bow."

The bow itself is loosely strung, "but not so that you can shoot arrows with it. I find that students tighten their bows much too much, to compensate for a lack of control."

His right wrist is low: "The reason you get false accents is that your wrist is too high, so your whole arm is weighted. I want to see a 'U' between the wrist and the forearm."

Concertos, running from Bach to Paganini, are clearly his favorites, and it was with evident disappointment that he discovered only one of the five Fairfax Symphony violinists subject to his musical dissection had prepared a concerto selection.

The first four violinists received gentle proddings and politely concealed winces from Fodor. But the last one, Michael Abramson, got extra attention.

Abramson ran through the First Movement from Mozart's "Fifth Violin Concerto in A" with some feeling for the drama Fodor brings to his performances, and Fodor's criticisms fell mainly along the lines of giving courage to the talented young man. At a difficult shift, Fodor urged Abramson to get his fingers in place before drawing his bow. "Don't be afraid of the shift -- it will just make you miss it."

Fodor long ago dropped any visible signs of fear, even in the tense atmosphere of competition. He finds these "a very unnatural arena for art," and after winning several and deciding his career was going well enough for a young man in his 20s, he decided to skip the prestigious Tchaikovsky arena.

But those running the contest kept the doors open for him "three months past the deadline," he says, so he finally entered -- and made it to the finals.

The welcome didn't seem to be as warm once he arrived in Moscow. The Soviets made it particularly difficult for Fodor to practice by scheduling his practice sessions with several pianists -- and his final performance was set for 11:15 one evening. Here's how Fodor tells it:

"I figured everyone (in the audience) would leave, since the Moscow subways close at 11:30. You can't get a taxi in Russia -- you can't get a sandwich in Russia -- so it would be a hardship for them.

"But they stayed in their seats, and heard me all the way to the last note. They they jumped up and ran for the doors, clapping as they left."

Fodor went from that victory to a White House engagement and a career that includes a lucrative recording contract with RCA and some 90 appearances each year. An interpreter rather than a composer, Fodor's ambitions run toward recording with Jorge Bolet and other acknowledged master musicians.

Fodor is adept at handling audiences awed by someone who has accomplished so much in such a short time. So when a fashionably dressed woman at a recent press conference cooed the inevitable, "What kind of person is Eugene Fodor," he answered without a trace of glibness:

"Very affectionate," he said.

His affections apparently include the Fairfax Symphony, which featured Fodor as the soloist at a concert this month.

After his performance, which observers called "breathtaking," Fodor told symphony conductor William Hudson that he hopes to return for the 1982-83 season.