Alfred Brendel began studing the piano when he was 6 years old, because his parents admired the way he sang. "They were not musical," recalls Brendel, who at 50 is generally recognized as one of the world's leading pianists, "but they noticed that I sang many songs correctly. I think they were quite bewildered later, when they found it would be a professional matter. Because they were not musicians, I had to find out many things on my own what others have learned from their parents -- but perhaps it was better that way."

Brendel, who was in Washington for a recital Saturday night at the Kennedy Center, was for years better known through his abundant recordings than through personal appearances in this country. He began recording when he was only 21, almost at the dawn of the LP era. He produced prodigiously for years, mostly on the Vox label, and by now has been able to record his second thoughts on a large part of his repertoire.

"My first recording was a Prokefiev concerto cor a company called Period," he recalls. "It is probably still around somewhere. It was made quickly and with very little preparation. They called me in December and asked me if I could record it at the end of January, and I told them, 'Yes; send me the music.' That was very courageous; I had never played a note of Prokofiev in my life. It was also courageous, perhaps, to record a complete Beethoven cycle when I was around 30." A trace of irony creeps into his carefully modulated, lightly accented voice.

In recent years, since he became affiliated exclusively with Philips, his recording activities have become more moderate. Like his style of playing, the Austrian pianist's career has shied away from overt spectacle. It has been building for more than 30 years, sine he won a prize ("not the first prize," he insists modestly) in the 1949 Busoni Competition. He describes his career as "more an unfolding than a succession of sudden changes," and as "a work in progress which can never really be finished."

His repertoire is still basically what it was in 1950, growing slowly and occasionally shifting a bit in emphasis, but completely consistent with its origins. He is an unusually thoughtful pianist -- or, rather, an unusually thoughtful human being whose personality is reflected in the way he plays the piano. Critics have called him "intellectual," or "the thinking pianist," but he objects to such descriptions if they imply an unbalanced, cerebal approach. Intellect acts as a control, a filter, he says, but feeling is "the alpha and omega for a musician . . . one must let oneself loose and control oneself at the same time."

Although he stopped taking regular piano lessons when he was 16 and began his career at 17, Brendel was not a child prodigy. He tends to find advantages in obstacles, and thinks his relatively unspectacular beginning was an advantage. "My career started itself out slowly while I was a teenage, and at first I was not at all sure I wanted to be a professional pianists," he says. "I also composed and painted, and of course, I wrote poetry like everyone. But after I won the prize, the piano became my choice, and I have never regretted it." He also has never regretted the slow start, he says, because it allowed him to learn his repertoire gradually and thoughtfully.

Although he performs everything from memory except a few 20th-century works like the Shoenberg Concerto ("just to be more comfortable"), Brendel does not have a photographic memory -- and that, too, he considers an advantage. "It saves a lot of time to have a photographic memory," he says, "but that may make things too easy. When I am preparing a season's programs, I try to forget as much as possible what I know about the music -- to reexamine what a composer wrote down, and perhaps reach a new conclusion. If one has to go back to the source, it may start a new chain of experiences."

It also leads to some nontraditional interpretations. In Schumann, for example, he says there has long been "a sort of consensus on what his music should sound like, a sort of warmth and tenderness that is not always easy to find in the music as it is written down. Schumann's music is often curious, with crazy, ironic and macabre traits that are not usually heard in traditional performances. I ask myself whether we have been living all this time with an image of his music that is not well-focuses. It may be that after hie death, his wife, Clara, may have tried to make his music appear more bourgeois than it is."

He has found similar distortions in many other places -- for example, Mozart's Concerto in A (now being called the "Elvira Madigan," a nickname which he dislikes). For years, he avoided playing it because he sensed something wrong in the first movement before pinning down the problem: the "Andante maestoso" marking which was not Mozart's idea but a 19th-century addition.

One previous distortion in our understanding of classical music, he believes, is a gross underestimation of how funny it often is. "Parts of the Diabelli Variations are hilarious," he says, "but no one ever laughs. Haydn is extremely witty and so is Mozart, but most of their wit goes unnoticed, although it must have been obvious to the people of their time."

One of his still unfulfilled ambitions is to write an essay on humor in music. He has already had one book published, "Musical Thoughts and Afterthoughts," and a large part of his aspirations relate to writing rather than playing the piano: a book on Beethoven's piano sonatas, an essay on silence, which he considers an important element in music, an essay on the Diabelli Variations, which he already has written in shorthand but needs to transcribe. But first, there are other commitments -- for example, the complete cycle of Beethovan sonatas that he plans to play in 11 cities in the 1982-83 season, and his family which has lived in London for the last 10 years -- his second wife, two small children, and a teen-age daughter who "writes her own pop songs, performs them with guitar and never goes to my concerts."