"I NEVER REMEMBER what I will be doing next," says Galina Vishnevskaya, who has left opera but not her intercontinental singing career. "I know that someone will put me on a plane to the right place, and that when I get there I will sing--I will have to give the best that I can, wherever it is. This has been my life since I was 17."

Vishnevskaya will be singing this week with Mstislav Rostropovich, her husband, conducting the National Symphony Orchestra. If the concert follows established patterns, it will be an intuitive collaboration that comes as close to lovemaking as anything that happens in classical music.

How do these two great musicians prepare for a performance of Shostakovich's brilliant, intense 14th Symphony? "We never spend time preparing our music together," Vishnevskaya said at lunch a few days ago. "We never rehearse together--or if we do, it is the night before the concert. Then, there is a huge quarrel and we don't talk to one another all the next day. Finally, when we go out on the stage together--that is the time when we try to please one another."

It is even more tempestuous--"a catastrophe," she calls it--when they try to prepare a new composition together. "It almost comes to fisticuffs," she says. "From the beginning, he would say one thing and I would say another."

In a city where her husband's figure dominates the musical landscape, Galina Vishnevskaya remains relatively unknown. This is partly because of personality; Rostropovich is one of the world's leading extroverts, while Vishnevskaya tends to be quiet, at least on public occasions--and only partly because of language problems. "I am a very private person," she confesses. "Sometimes, I think I turn people away because I am unable to engage in empty chitchat--but I don't mean to."

When they met and married, after a whirlwind courtship, Vishnevskaya was the prima diva of the Bolshoi opera--in effect, the musical Empress of all the Russias--a much bigger star than he was. She held this status for two decades and secured for herself a place in music history--except, perhaps, in the Soviet Union, where mention of her name is now systematically avoided in reference works and books about music.

Dozens of compositions have been written for and dedicated to her, and she inspired the soprano music in two of the greatest vocal works composed since World War II: Shostakovich's 14th Symphony and Britten's "War Requiem." (The latest work written for her is Ezra Laderman's 5th Symphony, which has a vocal part with a text taken from the Book of Isaiah: the passage about beating swords into plowshares. Vishnevskaya, still suffering from a flu recently contracted in Hong Kong, will be unable to sing the premiere performance. Her place will be taken by American soprano Lucy Shelton, a specialist in contemporary music with many world premieres to her credit.)

Vishnevskaya has at least two functional personalities. In public, she is the diva--the goddess--statuesque and regal in her bearing, reserved and usually silent except when it is time to sing. She fits into the role of the operatic star with evident ease, aided by striking good looks and the calm self-possession of one who has spent most of her life on stage. In private, a warm person emerges, a heart readily inclined to enthusiasm, tempered by a tinge of world-weariness. When she thinks she will be understood and accepted as a private person, her opinions are abundant, decisive and expressed with earthy vigor. She has known glory, gone everywhere, raised a family, and now thinks of settling down and living quietly--but wonders how she will be able to persuade her dynamo of a husband to decelerate with her. "I ask him to slow down," she says. "I don't think he needs to spend all his time working like a crazy horse."

The Rostropovich-Vishnevskaya union, musically and matrimonially, is an encounter of towering temperaments. "I don't think there is another marriage like it," she says; "I don't think there has been since the marriage of Robert and Clara Schumann." A tone of half-serious exasperation, wifely and artistic, creeps into her voice when her husband's name is brought up, and it is faithfully echoed in the voice of her translator, Nadia Efremov. Vishnevskaya's English is surprisingly good when she has something urgent to say in that language, but she prefers her native Russian when she is talking to the press.

"The many things we do together," she says, "I know that nobody else is capable of creating. Since he became involved with my music, I find I cannot do the same thing with any other. After all these years, he understands me better than anyone else, but also his abilities as a musician are so much greater. Everything I see after him is a great disappointment."

When they met and married, Rostropovich was known only as a cellist, though he had studied conducting. He is also an excellent pianist and sometimes plays piano accompaniment for her in her recitals, but his emergence as a conductor began at the Bolshoi and was directly related to his wife's work. "He started to conduct because of me," she says, "but not because I asked him to. I had sung with the Bolshoi for 15 years before he showed up there, and I didn't want him butting into my place. But I knew that sooner or later he would stick his nose into that part of my life, and he did. I think I am the primary cause in giving this conductor to the world--in spite of myself."

At a party last year, after her triumphant appearance in Tchaikovsky's "Iolanta" with the National Symphony Orchestra, Vishnevskaya turned to Rostropovich. "Cello!" she said, speaking in English with all the theatrical scorn available to a veteran prima donna. "When a cello string breaks, you get a new string . . . But try to get a new voice!"

Few singers could put it so eloquently, but this is the perennial complaint of any artist whose instrument is her body--an instrument that does not last for centuries as a cello does. Vishnevskaya was reflecting on a professional career that began with operetta in 1944, when she was 17 years old. In Paris last fall, that career reached a turning point when she sang her operatic farewell performance. The opera was Tchaikovsky's "Eugene Onegin," one of her greatest roles, and the reviews were enthusiastic.

At 56, Vishnevskaya's voice is no longer young, and it has never been completely problem-free, at least for tastes nourished in the western bel canto tradition. It is a voice in the Russian style, unique in timbre, heavily flavored with vibrato and somewhat uneven in dynamics at various points of its pitch range. These may be considered problems if total evenness of vocal production is set as the ideal, but Vishnevskaya has a dramatic power in her interpretations, a compelling quality in her ringing high notes, that can bring even a bel canto-oriented audience to its feet applauding wildly. That has happened in Washington in "Iolanta" and the "War Requiem," and may happen again in the Shostakovich this week.

Vishnevskaya does not mention vocal problems as a reason for her decision to leave opera. Through most of her career, her instrument has been not only her body but also, in a way, a whole opera company: the Bolshoi in Moscow, where she began to sing when she was 25 and became prima diva when she was 27. She has not been able to sing at the Bolshoi since she was sent into exile in 1974, and no other company (including the Metropolitan, Covent Garden, La Scala and the Paris Opera) has been quite the same to her.

"My career was connected to one theater in one city," she recalls. "I didn't tour in the Soviet Union; I would not live in drafty hotel rooms in order to sing with inferior companies, and overseas engagements were only an occasional thing . . . I was the favorite of the main conductors and the chief directors at the Bolshoi; my path was strewn with roses from beginning to end, no disappointments from beginning to end. The only problems came from political, not artistic, motives." She returns to the political problem, obliquely, a few minutes later, talking about operatic roles that she had wanted to sing and now never will. "I was saving them for later," she says simply. "I had not planned to become an exile."

Unlike many Russian artists now working in the United States--dancer Mikhail Baryshnikov, for example, or fellow Bolshoi soprano Renata Babak--Vishnevskaya and Rostropovich are not, strictly speaking, dissidents or defectors. They did not escape from the Soviet Union; they were ordered to leave, and a strong flavor of nostalgia--love of the land, mingled with bitterness toward its government--creeps into their voices whenever the subject comes up.

The chief reason for their exile, as far as they know, was their hospitality to Nobel prize-winning novelist Alexander Solzhenitsyn, whom they sheltered in their summer home for five years after the government made him a nonperson. "We gave him a home," Vishnevskaya recalls, "but we respected his right to a separate existence--one must have solitude for creativity. When I would come to the dacha to live, I might not see him for two or three months; I would respect his privacy because I know I need it myself. Sometimes I would look out the window and see him at the bottom of the garden, writing and pacing back and forth. Should I go down just to say 'Hello' and perhaps destroy his concentration for hours?"

Solzhenitsyn "controlled himself" in terms of public opposition to the government while he was living in the Rostropovich home, Vishnevskaya believes. "I think he tried to protect our family from the wrath of the authorities. Then he left our dacha, and six months later they threw him out. We were sorry to hear of this, but we didn't realize that we would be forced to follow him a month later."

Life in Moscow lasted long enough for Galina Vishnevskaya to raise two daughters (Elena, who is a pianist, and Olga, a cellist) to adulthood in a relatively stable environment. Both daughters went into exile with the family and are now married to fellow musicians. "I could not have had a proper family life as an international performer," Vishnevskaya says, "but it was possible because I was living and working in one city."

Exile has not been easy for Vishnevskaya. "What they did to me," she says, "it is like destroying your entire life. Now, I have a different life--that's over; it doesn't exist any more. In Russia, everything is turned upside down so easily and so often. Soviet history is remade over and over, like a pair of pants being retailored to a different height and build. In the end, you have to look into yourself and know that you have not willingly done anyone any harm. You cannot pay any attention to what is said by those dregs, who happen to be in power today but tomorrow will not even be worthy of the garbage heap. Their removing you from your pedestal is as meaningless as their raising themselves to their own pedestal."