The half-million-dollar Stradivarius had just rolled successfully through a National Airport metal detector. And its demure owner, 26-year-old Viktoria Mullova, was ambling down a dark corrider to catch her plane to Winnipeg, where she was to play two concerts.

Mullova, tall and chic, was in jeans and a dark sweater. And Mullova -- a brilliant musician who defected from the Soviet Union two years ago after winning one of music's ultimate prizes, the Tchaikovsky Competition's Gold Medal -- had her hands full. A bag and a heavy coat hung from her right arm. The Strad dangled from a finger of her right hand while the other fingers held a Coke. In her left hand she balanced a half-eaten hot dog.

It was too much to handle. So she said, "Here. Will you take this?" and you took custody of the Strad for the course of the ambulatory meal. The instrument is the so-called "Falk" Stradivarius, which she purchased in auction at Sotheby's in London last summer to replace the Soviet-owned Strad she had to leave behind when she hoodwinked officials and escaped with her fiance' during a tour of Finland. The Falk actually cost a little less than a half million, "but the pound has gone up since then," Mullova explained in the cool tones of her fluent English.

She had never been to Manitoba, which she was told would be an hour behind Washington and as frigid as Siberia. "Ugh!" she responded.

Mullova was to play in Canada and then rush back to Washington to play for President and Mrs. Reagan in last Sunday's "Christmas in Washington" program. Only eight days earlier she had made her Washington debut playing the Sibelius Concerto superbly with the Boston Symphony. And in the week before she recorded the Sibelius and Tchaikovsky concertos with the Boston Symphony.

Finally two seats were spotted near her boarding gate in the teeming early evening jam at the terminal. She sat down, plopping hot dog and all in her lap atop a half million dollars worth of violin.

"Now, what do you want to know?," she said mischievously, fully aware that little could be learned in the few minutes before she boarded her plane.

Mullova's escape belongs in the annals of Frederick Forsyth or Robert Ludlum.

It grew from a conspiracy between herself and and her fiance', Vakhtang Jordania, who was conductor of the Kharkov Symphony in the Ukraine and who, after spending a year or two with little employment in the United States, is now music director of the orchestra in Chattanooga, Tenn. They live in a small apartment on Manhattan's Upper West Side.

Mullova and Jordania, 43, met when he was asked to help prepare the young violinist for the Sibelius Competition in 1980, which she won.

She was, like most Soviet musicians, a product of the incredibly productive disciplines of the Moscow Conservatory -- the closest rival in the musical world to Juilliard. Her teacher there was Leonid Kogan, next to David Oistrakh the greatest Soviet violinist of his generation -- and no other country has produced so many great violinists as Russia. Even Isaac Stern was born there.

Jordania has said, "From the very first notes, I knew that she played big, like a great musician. We practiced in the afternoon and gave the concert that night. We have been together ever since."

He himself had won the Herbert Von Karajan Competition in West Berlin in 1971, but the Soviet Ministry of Culture would not allow him to travel and his hopes of conducting in the West had withered. It was his idea that they defect, leaving behind his wife and two children in the Soviet Union.

Deciding to defect and actually doing it, though, were two different things. The notion that the apparat would let the woman who had just won the Tchaikovsky Competition, plus her companion, defect was ludicrous. They talked about the possibility only on long walks and never within earshot of their families.

After the Tchaikovsky the world had not opened up the way Mullova had hoped. She was still a student at the Moscow Conservatory, and she was supposed to finish her studies. There was a tour of the Philippines, but that was because Imelda Marcos had attended the competition and insisted that she come. Other invitations were rejected.

Then, in early 1983, she was told she would be able to play in Helsinki in late June, but would have to find a new pianist.

Who else but Jordania? Except that he had not been allowed abroad since the Karajan. And he was not exactly a pianist.

In the Soviet Union, apparently, there are ways around trivia like that.

According to writer Joe Klein in an article in New York magazine, Mullova visited Tikhon Khrennikov, the head of the Union of Composers, a mediocre musician but a powerful man. "I visited him in his office and he was very friendly," Mullova told Klein. "I told him we were about to leave for Finland, and we were planning to play one of his pieces -- it would be featured, a debut outside the Soviet Union. But we were having a small problem with the bureaucracy, the KGB in Kharkov was moving slowly."

The KGB gave in the next day.

The two went to Finland on June 28, without even telling their families they would defect.

Reviews of Mullova were ecstatic and reviews of Jordania were negative, proving that music critics are not always wrong.

Mullova told the KGB woman chaperone to leave them alone because Jordania was "very depressed" by the reviews. Then, carrying two cherished violin bows in a plastic bag, they hailed a taxi and crossed the border into Sweden near dusk on July 2, 1983, but found the American Embassy closed when they got to Stockholm. It was Sunday.

"They told us the embassy would be closed the next day, too: July 4 -- Independence Day," Mullova told Klein. "We could not request asylum until July 5. We were very frightened. The Stockholm police told us to stay off the streets, stay in a hotel until the embassy opens. They gave us disguises."

The Americanization of Viktoria Mullova began long before she got here. The last book she read before coming west was "Gone With the Wind." "It took a whole month," she grunted.

In an interview at her hotel here on the day she played for the Reagans, she kept calling it "this mad, crazy life in America."

Why did she come west?

"Inner development. I could not live and die there. I could not continue to live as I used to. As a musician I feel it's important to feel free. I had terrible difficulty after the Tchaikovsky. I didn't have so many concerts. And when you have concerts you are ready to work and it's a big stimulation when you know you are playing this particular concerto. New repertoire. And with the great orchestras, then you really work. [Mullova, it should be noted, is playing this season at the Kennedy Center with both the Boston and Philadelphia orchestras -- a remarkable, possibly unique, circumstance in this city.]

"When you don't have the concerts how can you work? You can practice just for yourself, but it's better not to. Some musicians who stay in Russia, of course, play very well. But it is difficult to live like that. You get gray hair, white hair, very quickly.

"I had hoped to have lots of concerts immediately. I thought, you just defect, which is very difficult to do. And immediately after you come to the West, you play in Carnegie Hall with the best orchestras in the world. Because we have disinformation in the Soviet Union, we think everything here is fine, everything is fantastic, everybody has big houses, big cars. It's unbelievable.

"For me, it was not surprising that I had immediate concerts. But now I feel I was really lucky. But at the time, I thought it was quite normal. Because, as I said, I expected even more the first year. I didn't realize it usually takes two years ahead to plan a concert schedule."

Artistically, the experience in the West that Mullova returned to in conversation was the seven weeks she and Jordania spent last summer at Rudolf Serkin's esthetically unsurpassed summer festival at Marlboro in Vermont.

Twice she said, as if in wonder, "He is so serious about music." She and the great man, who is now 82, prepared the Beethoven C-minor Trio together. "It is his seriousness that makes him so special," Mullova declared. "He doesn't care about career or fame. He is this old man. But, in fact, he is very young.

"What he cares about is what is written by the composer . . . each dot, each crescendo. After that, it opened to myself so many things that I did not have before."

She continued on the subject of influences and came up with an unexpected one -- Maria Callas. "Listening to her recordings was so helpful," said Mullova. "She was great. Her phrasing. It was so musical. Sometimes it's hard to express how she does it, the way she builds her phrase. It's wonderful."

Then Mullova mentioned Jascha Heifetz: "There are so many things I admire." Then her fellow e'migre' Mstislav Rostropovich, who has been an adviser: "He is a great musician."

But she got back to Serkin in a funny context. She was asked if she wouldn't be a natural talk-show personality, like Luciano Pavarotti. She seemed to dismiss the idea, but not completely: "You can do it once. You can do it twice. And I understand that for the public it's important. Especially for the American public. So you have to do it." Then suddenly she blurted, "But can you imagine Serkin on the talk shows?"

At first, Mullova's optimism about the future seemed to know no bounds.

Then she started critiquing her playing:

"Many times I hate my playing. And then sometimes I don't hate it, but I am not satisfied. It is very rare when I am pleased. But as long as it happens, I am upset when something does not work well. But I know what is wrong, so I try to do better the next performance."

One crack in Mullova's optimism, though, finally showed -- rather starkly.

How about the family she left behind?

"I worry a lot, of course. And we were lucky. Nothing happened to them. Maybe it was because they did not know about [the plans for] my defection."

Does she ever expect to go back, the way her colleague Gidon Kremer does?

"No. Not even if the government said I could go, I wouldn't go. How can you put your life in such danger? Something can happen. And they can say it was an accident."

The grim look on that normally bewitching face told you: There is no question in her mind.