VIRTUOSI are the activators of music, Paul Valery once observed. In the large literature about performance, their insights breathe with immediacy and vitality. And among them, pianists, from Clementi and Hiller to Schnabel, Rosen, Brendel -- and Glenn Gould -- have been the most perceptive.

The World of the Concert Pianist consists of interviews with 36 keyboard artists who consider the interrelationships between composition and interpretation -- as well as their diverse ramifications -- in terms of what Anton Rubinstein called a "soloist's balance of personal understanding and feeling." The youngest is the controversial 26-year-old Yugoslavian-born Igor Pogorelich, whose international career began explosively when despite enthusiastic audience acclaim at the Chopin Competition in Warsaw in 1980, he was denied a prize. The oldest is the venerable Claudio Arrau, who at 81 has enjoyed world-wide success uninterruptedly for the past 70 years. Dubal's World also includes such luminaries as Ashkenazy, Ax, Badura- Skoda, Bar-Illan, Bishop-Kovacevich, Bolet, Brendel, Browning, Davidovich, de Larrocha, Dichter, Entremont, Firkusny, Fleisher, Gould, Graffman, Horowitz, Istomin, Janis, Johannesen, Johansen, Laredo, Ohlssohn, Perahia, Rosen, Sandor, Schiff, Peter Serkin, Tureck, V,as,ary, Watts, Weissenberg, and Wild -- truly a Who's Who of modern pianism.

Each responds succinctly to a brief sequence of questions (about three dozen) posed by Dubal, pianist, radio commentator and producer, and a member of the faculty of the Juilliard School. In general, the respondents are revealed in terms of what Harold Schonberg, Pulitzer Prize-winning critic of The New York Times, has called the virtuosi and the virtuous -- those for whom the act of performance represents an ultimate objective -- an end in itself -- and those who view it philosophically, fulfilling, in the words of distinguished German conductor Wilhelm Furtwaengler, "an act of musical destiny."

Thus Horowitz recalls his debut, when he wanted "to eat the public alive -- to drive them crazy" with his prowess; contrastingly, Fleisher recalls the observation of his teacher Arthur Schnabel, who compared the role of an interpreter to that of a mountain guide, whose presence, while increasingly important the higher the climbing, is always mindful of the fact that he must make his charge, the climber, more aware of the mountain than the guide.

As might be expected in such a collection of personal judgments, there is much shop- talk; the problems of tendonitis, the characteristics of hand formation, the subtleties of pedalling and fingering. There are also revelations ranging from naivet,e to cynicism, egocentricity to humility. De Larrocha: "I hate politics. It makes me sick to hear people even talking about politics"; Fleisher: "Today most critics are former garden or fashion editors"; Dichter: "Conducting is one of the last bastions of quackery left in the music world"; Graffman: "I knew the entire violin repertory by the time I was four"; Weissenberg: "For me there can be nothing more personal than to make music. Like love-making, it is the strongest expression of one's innermost self."

Occasionally there are deeply felt contemplations about art and the creative impulses it animates. Fleisher: "It takes us out of ourselves into a dimension of higher awareness"; Istomin: "Art has to do with the mind and the spirit, the reaching beyond the physical and the material, even the inexplicable"; Laredo: "The most inspired performances are aways those which are inexplicable from a logical point of view"; Vasary: "Through the keyhole of art, we can see ourselves clearly."

While The World of the Concert Pianist sometimes seems fragmented because of the impression of flitting from one subject to another, the sequence of ideas creates a lively kaleidoscope of individual reflections; it emerges as a world as diverse as its practitioners, all unified by the challenges of musical performance. Dubal has also included rudimentary biographies of persons mentioned during the discussions, as well as a selected discography for each of his interviews.

THROUGHOUT the pages of the World, Glenn Gould's name appears frequently -- cited with admiration by his colleagues for his beautiful tone, and the lucidity and rapturousness of his interpretations. But Gould, who died unexpectedly in 1982 at the age of 50, was more than a pianist: he was a charismatically versatile personality, an imaginative writer and producer of radio and television programs, and an original essayist with elegant command of the English language and a quirky wit comparable to that of Lewis Carroll.

Like Carroll, he epitomized the loneliness of artistic commitment. And in a profession whose practitioners frequently take themselves so seriously, he was capable of charming self-deprecation. He was also a bizarre musical recluse whose attempts at isolation and whose odd life-style fascinated both the press and the public. No one since the notorioous virtuoso Vladimir de Pachmann (1848-1933), who during concerts crawled under the piano ostensibly in search of the wrong notes he had played, exhibited more eccentricities as a performer. De Pachmann dipped his fingers into brandy before playing; Gould soaked his hands in scalding water. De Pachmann prepared for a concert by milking cows in order to limber his fingers; Gould meditated in the dark, avoiding all tactile contact with the piano. Onstage both fussed constantly with their piano chairs -- adjusting and readjusting the height; Gould's was extraordinarily low, making him appear almost as if crouching at the keyboard. And no artist ever presented himself before the public looking so unkempt -- hair uncombed, formal attire oversized and ill-fitting -- his white vest worn over a heavy woolen sweater, in avoidance of imaginary drafts -- for he was also a compulsive hypochondriac.

Gould as commentator is reflected in Conversations with Glenn Gould conducted by Jonathan Cott, journalist and poet. Originally published a decade ago as a two-part interview in Rolling Stone, they seem long, exuberant soliloquies, greater in scope and more flowing in continuity than Dubal's interviews. Gould's prose is always lyrical, his ideas frequently irreverent.

His imagination ranges far and wide. Considering Stokowski in terms of movie-making techniques, he comments: "He's a dissolve man and not a hard-cut man -- he cries out for a Visconti and not a Bergman." Of the Beatles, he reports being "appalled by what they did to pop music." Of piano technique he comments: "Everything there is to know about playing the piano can be taught in half an hour. I'm convinced of it."

And he explains the reasons for retiring from public appearances at the age of 32 -- to devote his performances to the recording studio. There he could subject his keyboard activities to "analytic dissection by microphone"; there he could control the environment.

GOULD THE ESSAYIST is revealed in the compilation of 68 articles which Tim Page, critic for The New York Times, has assembled from the hundreds which the pianist wrote during the second half of his lifetime -- beginning with "The Dodecaphonists' Dilemma," which dates from 1956 when he was 23. It is a remarkable anthology of characteristically uninhibited insights about music as art and craft -- from a proposal to ban applause at concerts, to praise for William Byrd, "the patron saint of the keyboard," and disapproval of Mozart's compositions, especially his well-known 40th symphony, which "consists of eight remarkable measures -- the series of unaccompanied falling sixths after the double bar in the finale, the spot where Mozart reaches out to greet the spirit of Anton Webern -- surrounded by a half-hour of banality."

There are concise appraisals of conductors: Joseph Krips -- "the only man who ever made Bruckner work": Willem Mengelberg -- "along with Stokowski, he was the greatest conductor I have ever heard on records."

And there is a penetrating comparison between a contrived television quiz program in which the answers are already known to the contestants, and a symphonic concert on film in which "we are confronted with a platoon of cellos arrayed in crescent formation, while in the next shot the same cello section is set out two by two with a single double bass bringing up the rear . . . almost every sound we hear, in the best post-van Doren tradition is faked. For anyone steeped in concert-hall traditions, this film will be an infuriating experience -- but I love it!"

Indeed, similar enthusiasm pervades the pages of this book, a magnificent testimonial to the mind of a musician whose scope of speculation and clarity of inquiry are unrivalled in the writings by performers.

Glenn Gould Variations -- newly reissued in paperback (Quill, $12.95) -- contains three articles by the pianist including a fascinating "Glenn Gould Interviews Glenn Gould About Glenn Gould." There are also perceptions of the artist by 18 of his friends and professional colleagues, among them Leonard Bernstein, Yehudi Menuhin, and Herbert van Karajan; writers Richard Kostelanetz and Joseph Roddy; editors Robert Fulford and Robert Stevenson; sculptor Joseph Dann; critic William Littler; film-maker Bruno Monsaingeon; and Gould's biographer Geoffrey Payzant.

Through their different keyholes, they focus upon Gould, the multi-faceted activator, and in so doing create a complex picture of the contemporary world of musical performance in which he was so idiosyncratically a central figure. CAPTION: Picture 1, Glenn Gould in Moscow; Photograph Copyright (c) Glenn Gould Estate; Picture 2, Glenn Gould with Leonard Bernstein in 1957. CBS Photo, Picture 3, Glenn Gould. Photograph Copyright (c) by Karsh of Ottawa