IN THE MID-1940s, in Buenos Aires, Bruno Leonardo Gelber used to go to the Teatro Colon to hear recitals by the great pianists -- Robinstein, Backhaus, Kempff and Serkin -- bringing with him another young piano student named Marta Argerich. Today, Gelber and Argerich are among the leading pianists from a continent that has been producing major pianists [more than great violinists or conductors] since the early days of Guiomar Novaes and Claudio Arrau. Both are international musical celebrities, jetting from continent to continent to fill busy performances schedules and known to wide audiences through their many recordings.

But then they were only 6 years old: budding prodigies who looked forward to the day when they would be giving recitals in the Teatro Colon.They were simultaneously enchanted and critical, as 6-year-old prodigies tend to be.

"We were allowed to sit in the orchestra pit, in the conductor's place," recalls Gelber, who was in Washington last week to play with the National Symphony Orchestra, "and our heads would stick up just a little beyound the rail, so that the people in the front rows knew we were there.

"When we heard a bad note, we would nudge one another, and the people in the first row, right behind us, would get very annoyed. They would tap us on the head and they would say, "These children have no musical sensitivity at all -- to act so disrespectfully when such a great artist is performing."

Three years later, Gelber was playing the piano on that same stage -- Beethoven's Third Concerto -- but in between, he had been stricken with polio [during the 1948 epidemic in Argentina, when he was 7 years old], and had made an amazing comeback.

The battle with polio marks one of the great dividing lines in a career that has added up to more than 1,900 concerts in 37 countries. The other major landmark was his winning of the third prize in the Long-Thibuad Competition in Paris when he was 18. "It was much better for me than if I had won first prize," Gelber recalls, "because it created a scandal. Everyone was talking about the 'injustice,' and everyone wanted to hear me."

The competition was held before an audience, and when the winners were announced, the crowd was indignant. "They were shouting 'Premier Gelber' ['Gelber First'], and they made it impossible to distribute the prizes," the pianist says with a reminiscent smile. "Finally, the police had to be called in. suddenly, I was being invited to give recitals and concerto performances everywhere. After that point, I have trouble talking about my career. It is too much, running from one continent to another and playing constantly."

As a child, Gelber recalls, "my life was like a dream. I had time for everything -- to learn, to practice and to grow naturally. Now it is all rushed, accelerated. I think I would like to give perhaps 20 concerts per year."

Gelber knew that he wanted to be a concert pianist very early in life, and the discovery horrified his parents, both of whom were musicians and thought that his life "would be sad" if he settled on a musical career. "My father was a member of the Colon Orchestra," Gelber recalls, slipping from one language to another with a facility that comes as part of an international career. "He wasalto, bratsche -- how do you say it? -- viola. My mother gave lessons at home, and when she was teaching I would stand very close to her and watch. At 2 years old, I would go to the piano after the lesson was over and pick out the theme with one finger. She began giving me lessons at 3 1/2, and she was very clever. She did not teach me to play by ear, as is usually done with children of that age, but she taught me to read, using a blackboard and different- colored pieces of chalk, so I was able to read music at 4, about the time I began to read words."

Later his parents tested him, he said, "to see if I was gifted to play before an audience, just as others are gifted to perform for an audience but not to play music. My father knew many great musicians, and he would bring them home to hear me play -- Karl Boehm and Arthur Rodzinski, Ferdinand Leitner, and Friedrich Guilda -- and I got used to playing for people. When I saw someone coming to the house, I would run to the bathroom and clean up and comb my hair -- and if they didn't ask me to play, I would ask them."

He made his public debut at 5, performing a Mozart sonata and [with his mother] a four-hand arrangement of part of a Beethoven symphony. "After this," he says, "she saw that the problem was quite serious, and she brought me to her teacher, Scaramuzza who told her that it was stupid to hesitate, I was born to be a musician."

Polio was a more significant obstacle to his career than parental objections. But by the time it struck, the 7-year-old Gelber was already a seasoned musician with dozens of public performances to his credit. It struck him chiefly in the legs (he still walks with a limp that makes him feel self-conscious) and he was bedridden for a whole year but not deprived of his music for long. "My only anxiety was one thing: Would I be able to play again?" he recalls. "I asked my mother, 'Will I walk again?' and she said, I don't know.' Then I asked her, 'Will I play again,' and she said, 'Of course,' although she didn't really know. My parents never gave me the feeling that everything was owed to me because I had polio, and my mother never let me know how upset she was, I saw her with red eyes, but I never saw her cry."

"After about a month, when they were sure that I could use my hands and arms, my father took the pedals off a piano and pushed my bed under it, so that I could play lying down. I played that way for months," Gelber says, holding his arms out a bit stiffly to show how to play a piano while lying flat in bed."After the first year, I gave a radio performance which was really a trio, with me playing the keyboard, my mother playing the pedals and my father holding me up on the piano bench."

A year after that, he gave a radio performance of Beethoven's Third Piano Concerto. By popular demand, this was repeated in public -- and then given again 20 days later.

Gelber feels that he was fortunate to be so young and resilient when he was stricken by polio, and that having the music to motivate him to recovery was "very helpful." When he was learning to walk again, his friendship with Argerich was also helpful, he says: "Marta would come to visit me, and when she was watching me, I would walk a little bit straighter." Looking back, he believes that his suffering from the illness was and is "primarily esthetic -- I am very sensitive to ugliness or awkwardness, and even my closest friends have never seen my legs."

But the aftereffects of the illness have also given special motivation to some of his activities -- a few years ago, for example, he raised nearly $100,000 for a hospital for handicapped children in Buenos Aires -- and he accepts it as a part of his life.

The life of a virtuoso pianist, flying from continent to continent, has some of the "sadness" that his parents had feared. "People like me have to learn to live exceptional lives, because to us the natural is exceptional," he says. "We have to leave personal life behind. The most important thing we have to learn is to be alone." Partly because of the constant travel and partly as a result of polio, he says, "affective relations are quite difficult for me."

Gelber still recalls the first concert he gave abroad, when he was 17. "I spent my whole fee," he says, "to bring my mother, father and sister with me -- to hear me play and, even more, to share the sensation of traveling by plane. The concert was in Chile, and the mountains are so high that we had to fly between them rather than over them. It was an extraordinary experience." When he went to Paris at 18, to study with the famed Marguerite Long, he was reluctant to leave his family and his father went with him for the first three months. Later, on his international tours, his mother would often go with him -- but now, he says sadly, "she is too old to travel."

Still, he says, the life he has chosen, the life for which he fought against a crushing illness, is the only one he wants: "If I am asked, 'Would you prefer to be a normal person with two good legs and have an ordinary life?' I would have to answer no. Making music is such a joy to me, and I feel that this is my mission in life, the meaning of my life."