ANDRES SEGOVIA began studying the violin when he was 6 years old. Fortunately for the guitar, his teacher was not very good.

"He was, himself, a mediocre player," Segovia still recalls 81 years later. "His tone and his sense of pitch were so poor that I rejected the violin as a musical instrument, and besides that he had a terrible temper. He would pinch me whenever I played a bad note."

During his visit here last week, Segovia showed once again what he has been demonstrating to the world through most of the 20th century: that the classical guitar, in the hands of a good musician, is a uniquely satisfying instrument.

He likes to compare it to "a small orchestra -- an orchestra seen through the wrong end of a pair of binoculars." He goes on at length about the guitar's variety of colors and the capacity for harmony and counterpoint, which enable it to play music beyond the reach of the violin or the cello. Ask him about the piano, and he will tell you the description he heard from a friend long ago: "a large, rectangular monster that screams when you touch its teeth."

He describes the sound of the guitar in a phrase he has used many times: "not voluminous, but luminous."

After a lifetime of missionary activity by Segovia -- now multiplied a hundredfold by his students and the students of his students -- people do not find it extraordinary to hear the quitar played as a classical instrument. But in the early 1900s, in the Spanish province of Jean when Segovia was growing up, the idea was shocking: The guitar was an instrument played by gypsies in taverns. And when the Segovia family became aware that young Andres wanted to be a professional guitarist, they were as shocked as they would be if he had chosen to be a bookie or a pimp.

Segovia is as much the gentlemen as the artist, and he phrases it a bit more gently: "My family recognized that I had received from heaven the vocation for music, but they wished that I would learn one of the instruments that were considered more noble than the guitar." But by then it was too late -- young Andres had fallen hopelessly in love. At the age of 87, he is still in love; his instrument is "she," and he speaks of her as a woman:

"You know that the guitar has feminine curves, and this influences her behavior. Sometimes it is possible to deal with her, but most of the time she is very sweet; and if you caress her properly, she will sing beautifully." He spends more than five months each year traveling with her, living in hotel rooms and airplanes ("I have a very sedentary life at the rate of 1,000 kilometers per hour," he remarks wryly), pays for her air ticket, puts her on the seat next to his own and calls her "Miss Segovia."

At home or on the road, they spend five hours together each day -- not continuously, but in four segments of about an hour and a quarter each, interrupted by meals, shaving, a stroll or other activities to stave off fatigue. He believes that longer hours than that are useless, and he states baldly that "artists who say they practice eight hours every day are liars or asses." Part of his daily practice, he says, is to "look through the stack of new music sent to me by composers." He holds his hand out horizontally as he says this, the palm downward, about a foot and a half above the floor, and touches an imaginary stack of new music for the guitar.

This new music is perhaps the most tangible sign of what the life of Andres Segovia has meant. When he came on the scene, the classical guitar repertoire was pitifully small and virtually unknown: a few neglected pieces by known composers such as Boccherini and Paganini and the work of good but relatively obscure 19th-century guitar specialists such as Sor and Giuliani. Today the guitar repertoire is large and rapidly growing. Nearly all of it in this century was written for Andres Segovia, and now it is being written for his students. "I have recorded more than 300 pieces," he says with obvious and justified pride -- not in himself, but in his instrument. "I do not commission new works," he says," but once they hear how their music can sound on the guitar, composers are eager to write for it."

It has been a long way from his boyhood enthusiasm to his present stature. When it became clear that he was serious about the guitar, friends began to help him find long-forgotten pieces of guitar music, and someone gave him an instruction manual. A flamenco guitarist showed him what he knew, but that did not take long and did not bring him very far, and there was nobody in Jaen who could teach him how to play his chosen instrument properly in the classical style.

"I became my own professor and my own student," he recalls. "Nobody can imagine the difficulty of learning without a teacher. I began to decipher the works of Tarrega, Giuliani and Sor. I observed a friend who was studying the piano, watched his fingers at work, and applied piano techniques to the guitar as well as I could." His aunt and uncle, with whom he was living, found that his constant attention to the guitar was interfering with his school work and threatened to break his instrument. Instead, he had a friend take the guitar away and leave it in a neighbor's home, where he would go to practice on the pretext of doing school work.

"Finally," he recalls, "when I was 16 and had a little bit of a repertoire, my friends pushed me to the stage -- it was in 1909 at the Centro Artistico in Granada. A friendly notice was printed in a small, provincial newspaper, and naively I thought that I had become world famous."

He quit school and went to Seville to continue his guitar studies and give concerts. Warmly welcomed by music lovers there, he found that his welcome had worn out a year later and decided to become what he has been ever since: a traveling performer. When he invited his fiancee to go with him to Madrid -- and eventually "the four corners of the earth" -- she asked him to stay, marry and get a regular job, playing the guitar for his own pleasure in his spare time. When he said that he had to go, she bade him farewell with a gypsy curse that he might lose his hands.

Segovia was by no means the only guitarist in Spain in the early 1900s, nor even the only classical guitarist, but being self-taught he had invented new techniques that have now become standard for all serious guitarists. One of his innovations, and probably the most important, was to make the guitar an instrument suitable for large concert halls and large audiences. One reason composers stopped writing for the guitar in the 19th century, after an interesting beginning had been made in the development of a guitar repertoire, was that concert halls began to grow larger.

Some instruments were modified to play more loudly for these halls -- most Stradivari violins, for example, were "improved" in the 19th century, and pianos developed stronger voices. Other instruments -- not only the guitar, but the flute and the oboe, for example -- had interesting solo music written for them in the 18th century but began to be neglected in the 19th because their voices were too gentle.

"Francisco Tarrega was composing and performing, but only for a small circle of friends and never in a room larger than this," Segovia says, looking around his room at the Watergate, which was large for a hotel room but not really large. "He thought it would be impossible to hear a guitar in a larger room. When I announced that I would play in a hall in Barcelona that seated 2,000 people, Tarrega's pupils were scandalized and thought I would be inaudible. But I had tested the hall very effeciently. I had the manager go to all corners of the hall and listen while I stood on the stage, snapping my fingers very softly, and he said he could hear me. Then I had him stand on the stage and snap his fingers while I went around and listened, and I was convinced that I could be heard all through the hall. By opening such halls to it, I opened the future of the guitar."

Not too widely, however. While he plays in large halls and makes himself audible to large audiences, Segovia refuses to use any kind of amplification. "It alters the beautiful sound of the guitar, nullifies it, renders it acid and metallic," he says passionately. "From a loudspeaker, you can still appreciate the artistry of the performer, the agility of his fingers, but you do not have the true sound of the instrument. I tell my students not to use amplification. Julian Bream does -- but this is not for artistic reasons. It is for commercial purposes, which I cannot accept."

After a career of more than 70 years, Segovia is able to look back with a satisfaction that he takes no pains to disguise. "I assigned myself four tasks for my career," he says. "To redeem the guitar from its flamenco associations, to develop a real musical repertoire for it, to travel to all civilized countries and play there in order to gain a following for it, and to influence conservatories to take the guitar into their curriculum at the same dignified level as the piano, the violin, the cello or the voice. I believe that all four of these tasks have been fulfilled. Did you know, for example, that in Japan alone there are now 2 million students of the guitar?"