The news came first when the phone rang in the modest Hartford, Conn., dwelling of the Jose Oliveiras about 11 p.m., July 5.

"On the other end of the line," explains Oliveira in his Portuguese-accented English, "someone says, 'We are sorry to bother you, Mr. Oliveira, but would you comment on your son's victory in Moscow? He has won a First Prize in the violin division of the Tchaikovsky Competition." I say, 'You sure you got the right number?' And anyway people are always doing things like that for jokes.

"But then this newspaper person read me the story, and I got my wife on the phone, and, there was no doubt about it, it was our Elmar.

"Of course, after something like that, you cannot sleep. So we sat up fretting," recalls Oliveira, "and about 4 a.m. the phone rang. I thought, 'Oh no, call at this hour is ever good news. But I was wrong and had forgotten about the time difference. It was Elmar on the line from Moscow. It was one of the most exciting moments of our lives."

Oliveira related the story of that tense evening yesterday as he and his wife stood beneath the glittering chandeliers of the White House at a presidential reception honoring the winners from Moscow. Both of them speak shyly with the accents of their Portuguese backgrounds and Mr. Oliveira grasps your hand firmly with his gnarled ones and smiles the ruddy face of a man who has spent his career out-of-doors as a master carpenter.

They came to Washington to hear President Carter honor their 28-year-old son, for his first-prize gold medal in the competition that the president described to several hundred guests as "the top competition among the world's musicians."

During a reception in the afternoon President Carter heaped praise upon Oliveria and the second American to win a gold medal, 30-year-old cellist Nathaniel Rosen. The president noted that it was the first time Americans have captured two gold medals in the Tchaikovsky, "and I'm certainly glad it happened while I was president."

The Carter speech was short. And then a receiving line was rapidly assembled at the entrance to the State Dining Room, with the senior Oliveiras getting swept up into it.

If the sequence of such a line really ruled in this city it would have meant that the Carters outranked the Oliveiras, because they came first, but that the Oliveiras were closer to the salt than Joan Mondale, who came after them.

The winner's mother, obviously a practical woman, realized that with seven persons in the line, counting the winners, things were just moving too slowly. So she told her husband, "We don't belong here." And they were escorted into the State Dining Room.

"It is wonderful just to be here, we don't want to get in the way," said Oliveira.

Without the skills of Oliveira the carpenter, his son might never have become Oliveira, the prize-winner. Elmar Oliveira's career literally began as a result of his father's carpentry skills. The father learned to make violins from scratch so that he could present his son with a small one at the age of 9. As Elmar grew, his father kept making larger ones for him.

One tends to think that violin-making must be the product of years of highly specialized apprenticeship. But not so for Oliveria, who set out to master the craft because he could not afford to buy instruments for his sons (an older son, John, is a first violinist with the Housten Symphony).

"There was a book that I read. "The Life and Work of Stradivarins,' and that was really all I had to know. it's not really so hard," he says with a modest tone that makes you think he honestly believes there is nothing exceptional about what he has done. "It only takes about 60 hours for the woodwork, you know. It's the glue that's all the trouble."

Some years the Tchaikovsky Competition is made into a highly political event, as when Nikita Khrushchev turned the 1958 victory of Van Cliburn into a propaganda vehicle for easing East-West relations.

But this year, the commissars stayed away, in tune with the political times. In fact, the president is the first important politician by whom either winner has been honored.

There were 260 competitors from 37 countries. "We all lived together in a single compound, and did little but sleep, eat and practice," recalls Rosen. "The competition is so great, there's no time for anything else. It's like a closed society contained inside another closed society."

During the competition, the American had little contact with the Soviet dissidents, and most did not even have news of how the Ginzburg and Scharansky trials were going.

After the contest was over, however, American violinist Daniel Heifetz, who won a fourth, sought out the mother of Ginzburg and donated to her his prize money of about $2,000, according to his representative, Robert N. Levin, who also handles Oliveira's affairs.

Both Gold Medal winners had their schedules pretty full over the next season, before the Moscow competition placed them in the spotlight. Rosen already records, on the Desmar label, and is probably tied up for this season since he is the Pittsburgh Symphony's first cellist. He had played two recitals here before and does not now have another scheduled.

As a result of his price Oliveira has been invited to play in the Pan American Union series in September.

Yet another news development in the annals of string-playing came with the revelation at the reception that Rosalynn Carter has given up the violin.

"I turned mine in about a month ago. You know I took it up when Amy did only because that's part of Amy's teacher's method. The idea is for the parent to get to know all the technicalities, so the parent can help in practice. . . . No, I'm not a candidate for the Tchaikovsky Competition, but Amy's doing just fine."