America's two gold medal winners in the Soviet Tchaikovsky music competition came to their supreme triumph from very different paths, but as they contemplate a future which in all probability will be richly rewarding, they speak of the same traditional wellsprings of self-confidence and creativity that have sustained musicians since the time of the Greek muse Terpsichore.

"Careers go up, down, sideways, everybody's career," mused Nathaniel Rosen, gold medal cellist, a few days after his success. "What's important is sustaining your own musical feeling, being plugged into constant growth.

"When you get down to it, you never reach the true meaning of a piece and can say, 'Well, I've played this piece as beautifully as possible.' You can't say that. I really never had that feeling. And when occasionally I thought I did, I've enjoyed it, but then I think to myself, what will I think about it in a month or a year from now, maybe I'll feel much differently about how I played it. That's the way I want to be, that's the way I am and I want to continue that way."

Elmar Maria Olievira, the American who tied for the gold medal with a Soviet in the violin competition her, spoke of it this way: "When you look at a painting, it's always within the same canvas, but there are a million different strokes.You always see something different though the painting is the same. Music is like this. You can always play it in basically the same frame, but each time there is something new, something different."

At the center of this fascination with each piece they perform is the incredile repertoire of the contemporary classical musician. Rosen at 30 and Oliveira at 28 have probably lived longer with their musical repertoires than most have lived with their spouses parents, siblings, lovers. And they probably know their music better than one knows those partners in life. Yet it is a knowledge that is not limiting, a familiarity that breeds no contempt.

Oliveira began playing violin, at the urging of his father, a carpenter, at the age of 9 in the Connecticut town of Naugatuck. "I've lived with the basic repertoire most of my life," he says. "A solo career starts at 11, 12 years of age. If you don't start playing young, it's very difficult later."

In his head, fingers and heart are, by his calculation, "all the standard concerti, the standard sonatas, shorter pieces, concertos that are not played very often and much contemporary music. A lot of this stuff you live with."

Rosen began playing cello also at the urging of his father, David Rosen, then a lawyer and now a workmen's compensation judge in California. Rosen was 6 when he began. His experience with his instrument has been, you might say, typically californian. Whereas Oliveira has honed his music virtually completely within the classical as well as rock 'n' roll, commercial advertising jingles, dance bands and the like on his way to Moscow in America, where classical music a triumph "that will help focus life toward one of those playing experiences above all others."

But he worries, as does Oliveira, of the uniform demands of mass culture in America, where classical music mu-audiences have laid down for the most part clear ideas to their cities' concertmasters what they will pay to hear and what they don't want to hear ever again or even for a first time.

"People complain that the cello has a small repertoire, but that's because great cellists are always asked to play the Dvorak concerto. Nobody asks them to play the Saint-Saens Second. And if the artist is interested in playing the Saint-Saens, even in suggesting it, then the answer will be, 'No, let's play the Dvorak that we played two years ago, it was such as success.'"

This poses the musician with the tough time of struggling to overcome ennui and going out there once more to saw away at the same piece night after night. "It's kind of disagreeable," Rosen concedes, "but it's very hard to avoid, not because you want it, but because they want it."

He contemplated the situation of Van Cliburn, the American who became a musical sensation by winning the gold medal for piano in the first Tchaikovsky competition 20 years ago. "He continues to draw tremendous crowds wherever he plays. He's very much in the business of playing piano. In his case, it seems he's offered major opportunities to come and play the Tchaikovsky First (piano concerto, which Cliburn played in the final of the competition to stupendous accolades from the Russians). You don't say no. That's what people want to hear, that's what the people fill the hall for."

Rosen has played with the Los Angeles Chamber Orchestra under Neville Marriner and now is principal cellist with the Pittsburgh Symphony Orchestra, which is under the baton of Andre Previn, whom Rosen describes as "my friend." An outgoing and humorous man, Rosen spent a year honing his pieces for the competition.

"There wasn't a day gone by in which I didn't say, "Did I really do it today, did I get a little better on this piece?" It wraps your whole attitude on music, there's something back there (in the back of the mind) that's saying. I gotta play better than anyone else. Gotta make sure I don't do anything the jury won't like. Who knows what they like? The jury obviously wants to hear something beautiful, but I can't be thinking about anything beautiful and be thinking at the same moment about how someone else is going to play beautifully. There's a lot of conflict there. You don't really grow, you might get more refined in playing, but not grow. You box yourself in by having a competitive mentality."

Oliveira, of Portuguese descent, studied under Raphael Bronstein in New York for 79 years and about eight years ago began his professional career, performing solo violin and getting concerts wherever he could. He is now averaging between 20 and 40 concerts a year. "I suspect they will go up now," he says with undue modesty. He left Bronstein's tutelage and the safety of the Hartt Music School in Hartford, Conn., where Bronstein taught, when he decided the difficult question of whether he was ready for a professional career.

"You have to have conviction in what you're doing, you go out and perform and develop and grow on your own. You leave your teacher when you know the teacher has given as much as he can for the time being, and throughout the rest of your artistic life, you draw from different areas, go back and play for your teacher at different times, and learn from this."

Oliveira's father, Jose, also makes violins, and Elmar ("it means the sea"), is pleased to say that he himself can perform minor repairs on his instruments if the need arises. An older brother, John Oliveira, is first violinist with the Houston Symphony, and a second brother, Joseph, works in a chemical factory in Connecticut.

Solo performance, with its demanding requirements of technical perfection and the intense audience involvement it draws, "is the toughest of all playing," according to Oliveira. "It takes a special amount of time, energy, skill, patience, struggle. Anyone can step out of a conservatory, audition and get into an orchestra. But a solo career starts at 11 or 12."

The intensity of the experience of the soloist confronting his music and his audience fascinates Rosen. "The ideals just to concentrate on what you're doing all the time - don't look at the audience, don't notice them, and when there is a breath in the music, then you can feel whether they are tuned in or tuned out. You can feel someone listening . . ."

Rosen is married to Jennifer Langham, herself a professional cellist, and they live in Pittsburgh. Oliveira lives in Binghamton, N.Y., a place he chose because it isn't too far from New York City (3 1/2-hour commute) and is yet beautiful and quiet. He practices and gives a select number of private lessons to talented students.

Both men know that they are on the brink of great artistic and financial opportunity. Oliveira declined to discuss his contractual arrangements with any specificity, beyond conceding that he has been contacted by record companies interested in signing him. Rosen feels that the terms of his two-year contract with the Pittsburgh are going to be enhanced by his victory.

And yet, as Rosen said, careers go every which way. The test comes in whether they will be true to themselves and their music.