When he was very young, Andres Segovia likes to recall, he once said a little prayer: "Lord, I am a very bad sinner who does not deserve your glory, so please leave me here on earth ."

Evidently, it worked; Segovia will celebrate his 93rd birthday next Friday. This year marks, believe it or not, the 70th anniversary of his first international tour. And he still plays to packed houses when he takes his guitar on the road, as he will in Washington next month.

When he began, Segovia has often said, "The guitar . . . was played only in cabarets, by Gypsies." That is a slight exaggeration; there were a few classical guitarists in Spain when Segovia was growing up, but none of any great stature, none performing in the province of Jae'n where he lived and no teacher capable of bringing out the full potential of a student as gifted as Segovia. He learned some basics of technique from a flamenco player and then became his own teacher.

Segovia's parents wanted him to become a lawyer or, if he had to be a musician, to play an instrument with some class: violin or piano. He tried and couldn't; he was born to play the guitar, he fell in love with it at first hearing, and he felt he was destined to find for it its true place in the world of music.

Today, he can look back and say that he has done exactly that.

When Segovia began, the guitar seemed to be an instrument with a promising past and no future. It had enjoyed a boom in the early 19th century. For a while, even the great Paganini abandoned the violin to perform as a guitar virtuoso, and there were several other fine guitarist-composers such as Fernando Sor and Mauro Giuliani -- not to mention Hector Berlioz, who was a guitarist but wrote almost no significant music for the instrument.

Today, largely through Segovia's efforts, the guitar is accorded a unique place among classical instruments. It is the only instrument in general use for classical music (let's forget about the accordion and the harmonica) that a performer can carry on stage, tune by himself and use for a musically complete performance, including harmony and counterpoint, without any kind of accompaniment.

The violin or cello can play limited harmonies for a while, thanks largely to the music of Johann Sebastian Bach. A player of monumental stature can hold an audience for a whole concert devoted to such music -- perhaps once or twice a year. But over a prolonged period, the process can become torture for audience and player alike. In its musical resources, the instrument the guitar most resembles is the cumbersome piano. It lacks the piano's range of expressionparticularly in terms of violence -- but it is like the piano in its ability to give complete and prolonged musical satisfaction without outside assistance.

In the early 19th century, at a crucial stage in its history, the guitar lacked three elements it needed to reach its full potential: great performers, great teachers and a wide audience. It could not reach the audience because of its physical limitations. For the guitar, the development of large concert halls in the later 19th century was a social disaster; the instrument's gentle voice simply could not match the new acoustics. The piano, faced with the same problem, evolved from the less assertive fortepiano into the roaring concert grand of today, but the guitar was physically incapable of such change.

If it had been possible (as it is today with amplification), the evolution would have altered the instrument's character beyond recognition. In fact, the introduction of amplification has changed the pop guitar into a completely different instrument -- not necessarily a monster but capable of becoming one if it falls (as it often does) into the wrong hands.

There are techniques for making an unamplified guitar's sound fill a fairly large hall, but the world had to wait until Segovia discovered them. Technique in general was a problem in the last century; it had simply not developed to the level where the guitar was capable of playing music as complex and expressive as that which was being written for the violin and the piano -- not to mention the symphony orchestra. Segovia was needed to show the way.

Ultimately, it is impossible for one performer to precipitate an instrument's renaissance. Besides giving an example of what could be done with the guitar, Segovia has been a very busy and productive teacher. At the beginning, he stood alone; today, he is surrounded by colleagues. There are hundreds of professional classical guitarists and dozens who have an international following. Quite a few are now technically better equipped than Segovia in his advanced years, though none can hope to achieve the stature thrust upon him by his historical position. Many are his students or the students of his students; all are beneficiaries of the possibilities he has revealed, the audiences he has built and the compositions he has inspired.

Sor is sometimes called "the Beethoven of the guitar," but the truth is that the guitar is still waiting for its Beethoven. The music composed for it in the 19th century is often charming and ingenious but lacks greatness. Segovia has not served his instrument as a composer -- at least not publicly. It is reported that he has composed music for the guitar but decided to withhold it from publication until after his death so that other guitarists will not have to worry about having their performances compared with his.

In any case, Segovia has inspired composers to take a new look at his neglected instrument. If nobody quite as good as Beethoven has composed anything for the guitar lately, the same complaint might be made about all the other classical instruments. And, inspired by Segovia and the guitarists of later generations (Julian Bream, John Williams and Narciso Yepes, to name only three), composers as diverse as Heitor Villa-Lobos and Benjamin Britten have produced masterpieces for the instrument. Joaquin Rodrigo's "Concierto de Aranjuez" -- for many listeners a revelation of the guitar's expressive and coloristic possibilities -- is one of the few works by a living composer lodged firmly in the classical top 40.

In a sense, Segovia consciously devoted his life to missionary work; in another sense, his entire career has been a love affair with an inanimate object -- inanimate, that is, until he touches it and the strings come to life. He decided while very young to show the world that the guitar was an instrument worth hearing, and he has done that brilliantly. When he talks about the guitar as a musical instrument, he calls it "a small orchestra -- an orchestra seen through the wrong end of a pair of binoculars," and in his hands, that is exactly what it is. It becomes capable of an enormous variety of expressions, though its natural tendency is toward tenderness, highlighted with rhythmic and harmonic excitement. It is not a good instrument for anger or grandiose fantasies -- and if it were, it probably would not have attracted a player as unassuming as Segovia.

When he talks about the guitar as a friend, Segovia inevitably compares this most intimate of all instruments to a woman. "You know that the guitar has feminine curves," he once told me, "and this influences her behavior. Sometimes it is impossible to deal with her, but most of the time she is very sweet; and if you caress her properly, she will sing very beautifully." When he flies with his guitar, he buys an airline ticket for her, refers to her as "Miss Segovia" and straps her into the seat next to his own.

Segovia is the last of the giants who revolutionized music earlier in this century by putting the spotlight on previously forgotten or neglected instruments. Like Wanda Landowska on the harpsichord and Pablo Casals on the cello, his biography is a large segment in the total history of his instrument.

When his Washington fans flock to the Kennedy Center to see and hear Andres Segovia next month, they will be participating in something like a religious ritual. At a Segovia concert, there is a silence in the audience like the silence at no other musical event. This is partly because the instrument needs and deserves such respectful treatment. But mostly it is because the audience knows that the figure on the stage is more than a man; he is a monument.