Claudio Arrau

One of this century's titans of the keyboard looks like anything but. As the house lights dim, a man who could be Chile's answer to Charlie Chaplin waddles penguinlike to center stage. Half as high as the open Steinway piano, he sits on the bench, his feet barely touching the pedals.

Except for tie and tails, Claudio Arrau resembles a kindergartner at the wheel of a Mack truck.

Yet, in a world of supervirtuosos, where superlatives fly faster than Liszt's transcendental etudes, this bantam is known understatedly as ''his serene highness.''

This means that at an Arrau concert, pianistic display, speed, and power do not reign supreme. Sublime artistry does.

Whereas more restless performers aim for high-velocity, bravura performances that excite the visceral senses, maestro Arrau aims to produce aural architecture - sculpture in sound. Celebrating his 80th birthday this year after performing in public since he was 5, Arrau is more on target than ever, critics say.

''It's not that he doesn't play with fire,'' says Robert Silverman, editor of Piano Quarterly. ''It's that he doesn't ignite just to put smoke in the room, but, rather, to burn at a steady pace - flame with the added dimension of temperament.''

In Avery Fisher Hall for the concert that will kick off Arrau's anniversary year, the anticipation in the air is so thick it seems to be forming clouds on stage, even in this city where gala events are as common as street vendors. The capacity audience is buzzing, because this German-trained prodigy-cum-legend is playing much better than at his Golden Anniversary performance. That was 25 years ago. Arrau eases gently into Beethoven's ''Waldstein'' sonata. Eyes close and ears turn. A woman well back in the theater remarks to her husband: ''I've listened to this piece a thousand times; he still shows me notes I've never heard before.''

Arrau has devoted his life to pursuing what he calls ''the total fusion of virtuosity and meaning.'' To him, the pianist cannot just be a player of notes.

''I believe in general culture,'' he says. ''I don't believe in specialization. If you just spend your time practicing scales and exercises, you cannot gain much. But if, for instance, you suddenly come to understand the paintings of Turner, that understanding will suddenly work back on your interpretation of Debussy.''

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* Another sonata, then Debussy, Liszt, and Chopin pieces, and there is thunderous applause. Maestro Arrau nods endlessly, but refuses to play an encore. As he bows, he is nudged by one end of a tea cart pushed by a handsome young man and adorned with a piano-shaped cake. A few telegrams are read - President and Mrs. Reagan's among them. Then the man with the tea cart leads the crowd in singing ''Happy Birthday'' in an exquisite tenor every bit as good as Placido Domingo's.

Claudio Arrau is moved and later shaken to find out that the man was Placido Domingo.

''The singing was too marvelous a thing, yes?'' Arrau says back in his dressing room, the doorway choked with admirers. His respect for voice goes back to his philosophy that all music has its roots in singing. He thinks the pianist can learn much about artful, truly musical piano playing by singing each phrase first.

Since the piano doesn't need to breathe, he says, many unnaturally fast tempos or interval changes are forced by performers wanting to show off their manual dexterity. The piano becomes more a separate instrument rather than an extension of the artist. Inimitable human grace and beauty are inevitably lost, he says.

Although Arrau occasionally chats with followers in one or more of the seven languages he speaks, he has perfected a polite, nodding muteness to keep the attention from piling up on him. ''That's enough,'' he finally blurts to one man who is carrying on about Arrau's interpretation of the Debussy.

It's not only Arrau's interpretation of Debussy that astounds critics. He has the largest repertoire of any exponent, present or past. He became a legend in Germany in 1935, when he played the complete keyboard works of Bach in 12 recitals. He followed with all 32 Beethoven sonatas, the Mozart sonatas, as well as all of Schubert, Debussy, and Carl Maria von Weber.

He has also performed - although not in cycle - all the works of Chopin and Liszt and much of Isaac Albeniz, Ravel, and Schonberg, each with vastly different demands on the hands, fingers, arms, and musical intellect.

Just after World War II, London Times critic William Mann wrote: ''There are pianists who rank as outstanding in Bach, Mozart, Chopin, and Lizst. Arrau is the only pianist alive who can convince people that he is the outstanding interpreter of all these composers and a good many others too.''

Another journalist figured out that it would take 72 recitals of 21/2 hours each to exhaust Arrau's repertoire.

''I don't regard it as healthy,'' Arrau says of the practice of specializing in a handful of composers, as virtually all other pianists do. ''I have always thought that the wider range an interpreter has, the deeper he will understand everything he plays. By understanding a composer's total oeuvre, one can better interpret the individual pieces to his life puzzle.''

The Arrau home in Douglaston on Long Island mirrors the pianist's love of diversity. The rooms are decorated with Byzantine and Eastern European icons and African, Etruscan, and pre-Columbian figurines from a lifetime of world travels. A concert Steinway stands in front of the far wall, and through the window is a view of Long Island Sound.

There are also ceiling-to-floor bookshelves - ''I wish for a hundred years just to read,'' he says - packed with scores of books on art, architecture, opera, and all the famous composers. And reading about a composer's life is not just an academic exercise he pursues for aesthetic pleasure or even professional background. Arrau applies what he learns directly to the concert hall.

Take, for instance, his feelings on Bach:

''To insert crescendos and diminuendos into the music of Bach is to insert an element foreign to his time and to a world which was rooted in the spiritual essence of the Middle Ages. It is only when the philosophy of writing music changed, when the music became so very personal, that the use of a wider dynamic range and dynamic arching became valid. When music started to express passion and sensuousness and romantic feelings, it coincided with the invention of the piano itself. So I think that certain rules should be set up to interpret Bach on the modern piano.''

Arrau learned the musical language early. In 1908, at age 5, he was invited to play for the President of Chile. The young prodigy astounded his listeners by sight reading sophisticated works that he'd never seen before. He identified the composers of other works merely by seeing scores of their music. He mentally transposed works from one key to another, reading them in E-flat for example, while playing in D-major. And he identified all the notes in a chord played by another person while his back was turned.

''Today we have among us a prodigy who, at this early stage in his life, can be compared to Mozart,'' gushed the Chilean magazine Selecta afterward.

Today, Santiago, the Chilean capital, and Chillan, the town of his birth, both have streets named after him.

At age 10 he was awarded a 10-year scholarship to study abroad. He took his mother, two sisters, and aunt (his father passed on when Claudio was 1) to Berlin. He located the famous teacher, Martin Krause, a pupil of Lizst. After tryouts, Krause remarked on Arrau, ''He will be my masterwork.''

''Part of his way of teaching,'' says Arrau, ''was to insist that I develop gradually. For instance, he would never let me play late Beethoven in public. 'You think about it and try to understand it,' he would tell me, 'but never play it in public until you are quite sure you have come close to the meaning.'

''This is an area where I sometimes disagree with young pianists. They want to play everything right away, even the most problematic and difficult works. One has to be very careful to let certain works mature - but young people lack patience today.''

Once an established European star, Arrou came to the United States with a promised tour schedule of 30 dates. But after a poor reception at Carnegie Hall in New York, the number dwindled to five.

''That poor reception was quite a shock, because I had been playing successfully all over Europe and Russia with terrific adulation. I stayed away nearly two decades after that,'' Arrau says. When he did return, older and more mature, his concerts became sellouts.

It is reported that since then, during more than 40 years, there has not been a single month that he has not been playing somewhere in the world. Tours in 1968 and 1974-75 took him to the Soviet Union, Japan, Australia, New Zealand, Mexico, South America, and Israel, as well as through the US and Canada.

This year Arrau has been nearly as busy: special concerts in Paris, Berlin, Bonn, and London. He will finish with recitals at the Salzburg and Edinburgh Festivals and at the Vienna Musikverein in August, September, and October.

The Arrau discography is as vast as his repertoire. Since he began to record in his early 20s (he is still at it), the resulting stack includes all the Beethoven sonatas and concertos, both Brahms concertos, most of Chopin, Debussy, Schubert, Tchaikovsky, Schumann, and Liszt. Philips Records (his label since 1963) has just announced a reissue of 59 albums in eight deluxe boxes to celebrate his 80th birthday.Three other companies, CBS Records, EMI, and RCA-Paris, are also bringing out reissues for the celebration.

''One has to fight vanity,'' he says in soft tones with a slight accent. ''I found out about the blocks it can produce against creativity. You must learn not to try to play better than everyone else, but to find your own message and interpretations - wedded to that of the composer, of course.''

Arrau is engaging and grandfatherly. Mustachioed, hair neither quite gray nor black, he is a dapper figure in a three-piece business suit. Joseph Horowitz, in his recently published ''Conversations with Arrau'' (Alfred A. Knopf, New York, cynical, least devious, of men.''

Although he once played Schonberg, Stravinsky, Bartok, Copland, and other contemporary composers, he has long stayed away from modern music.

''It had to do with . . . what audiences were ready to hear,'' he says. ''I'm thinking of (Pierre) Boulez, (Karlheinz) Stockhausen, and (Luciano) Berio. I do not say that I will play them yet, but I'd like to.''

His favorite composer, however, is ''whoever I am playing at the moment.''

Audiences, he thinks, ''have improved tremendously in taste and interest over the years. ''I feel you can play anything anywhere, as long as you do it well and with understanding. It's a wonderful thing that's been happening.''

Weeks after the Avery Fisher Hall recital, Peter G. Davis wrote in New York Magazine:

''Well, Rubinstein has left us, Horowitz surfaces erratically when the spirit moves him, and Serkin gives just one New York recital a season. Only Arrau continues to play steadily and with the energy of a youngster . . . he has not lost sight of a performing musician's basic mission - to play great music in front of an audience in quest of the deepest musical values.''