In his baggy gray trousers and rumpled tweed coat, the bespectacled Maurizio Pollini looks more like Woody Allen than a brilliant pianist with a Horowitz-size future. In contrast to his polished concert decorum, there is a genial disarray to Pollini's off-hours in the Watergate suite where he is staying during this week's visit as guest artist with Mstislav Rostropovich and the National Symphony Orchestra.

In an age of superstar self-promotion, the 39-year-old Italian behaves like a Brahmsian recluse, limiting his touring and shying away from publicity. His artistic biography is a model of taciturn brevity. The available facts make it seem that his genius sprang almost full-blown at the age of 18, when his first-place winning performance at the Warsaw Competition prompted Arthur Rubinstein to call him a "colossal talent," adding the opinion that "in his fingers he has more skill than any of the rest of us."

Since then, critics have ranked him among the handful of great pianists in his generation. But when asked about the comparisons to such keyboard giants as Horowitz, Pollini throws his hands up into the air, "Oh, no, no, no!" and reaches about for a cigarette. "Oh, please! Don't make me think about it!"

Which pianists does he particularly admire? "Do you mean when growing up? Many. Schnabel, of course, and I was able to listen to Cortot in the very last concerts. And Rubinstein was playing all the time in Milan.

"Today I like very much Serkin, who I find is a deep interpreter of music from Bach to Brahms." He reaches for another cigarette and sits back. Suddenly he lurches forward again, determined to be precise, to omit nothing.

"Of course, Horowitz and Michelangeli, Bachauer . . ." He gestures impatiently. "There is a whole list."

"It was always clear that music was my main field," says Pollini, whose father was a prominent Milanese architect. Studying piano privately and at Milan's Verdi Conservatory, he made his first public appearance at age 11. After his Warsaw win in 1960 he worked for a year with the noted pianist, Benedetti Michelangeli, and then spent several years in relative seclusion, giving few concerts. In the late '60s Pollini emerged with an interpretive depth to match his astounding technical command, reaping in the past decade critical notices steeped in superlatives.

In the last 10 years he has played with all the major orchestras in Europe and America, including the Berlin Philharmonic, the Vienna Philharmonic, the London Symphony, and the Boston, Chicago, New York, Philadelphia and Cleveland symphonies. His recording of the two Bartok piano concertos with Claudio Abbado and the Chicago Symphony won the 1979 orchestra.

In preparing a work, Pollini says, knowledge of tradition helps, but "it is also helpful to look at a composition as if for the first time, to have a personal approach. Of course, playing the music of many composers is a danger, but it's an adventure that makes the musician's life worthwhile for me."

Pressed to explain the danger, Pollini, who is known for his exceptionally broad repertoire, says: "Because it's very difficult to be convincing. In a certain sense every performance is a risk, though it's quite clear that there is a concept and a structure that holds the adventure together."

To build his concepts Pollini immerses himself in the thought process of a composer, becoming familiar with as much of his total output as possible. He studies manuscripts and sketchbooks -- Wednesday was spent inspecting the collection at the Library of Congress.

"I'm sure that composing is the biggest adventure," he said. "To look at the original sketch of the first movement of Beethoven's Op. 31, No. 2 [a sonata Pollini played last weekend in his NIH program], for example, was incredible. On a piece of paper less big than this" -- he points to a stenographic tablet -- "the whole idea was there. The whole movement apparently took Beethoven in one moment."

Told that his formidable technique makes piano-playing seem easy, Pollini laughs. "I think there is nothing easy and sometimes the most apparently easy is the most difficult -- a very simple theme by Mozart, for example." But, he says, "I'm not somebody who in any occasion practices six hours a day -- no -- but still I work constantly. I practice more some days than others."

Pollini, who lives in Milan with his wife and 2-year-old son, says that the life of a globe-trotting musician does not appeal to him. He confines his touring to America and Japan, making only isolated appearances in Europe after which he returns to Milan. His wife and son will be coming to America next week to join him for the rest of this American tour, which ends April 10, and then go on with him to Japan.

He grows effusive on the subject of his son, who will be making his third trip to the United States. "He has started listening to music -- by his own wish, absolutely. Apparently, he wants to listen to records," he says, denying that wants to turn him into a musician. "No, I just want to let him find himself, be happy in some way.

"But Rostropovich insists on teaching him the cello," he adds, laughing. "In fact, when he was born, Rostropovich sent me a telegram saying, 'Congratulations on the new cellist.'"

Asked if his life is all music, Pollini gives a laugh and the teasing reply, "Almost."

Would he care to elaborate on that "almost"? He looks about anxiously, unable to muster a diverting laugh or shrug. "Do you know the time? I think I must be going." With obvious distress he learns that five minutes are left in the hour he has promised. He lights another cigarette. "Well, you go to museums, you read, you see friends, et cetera. And there's a little bit of time in the summer at the sea" -- a slight pause, this time for dramatic effect -- "with no music at all." And he smiles broadly at his impish coda.

But it turns out to be a false coda. With the same intense concern for detail that he brings to his performances, Pollini calls back later in the day, concerned that he has perhaps sounded too romantic. "Though I speak of adventure," he says with imsistent humility, "you know of course that fidelity to the text is implicit. It is not something wild and free. To enter into the mind of the composer is a constant preoccuption. One succeeds more or less."