To the political revolutionary, the words "golden age" imply the future; to the lover of classical music, they imply the past. Often, it is the not-too-distant past -- perhaps because no music sounds so sweet as what we heard with teen-aged ears. Whatever the reason, writings on music through the centuries abound in descriptions and reminiscences of a golden age just gone by. Seldom does anyone use the expression in the present tense.

But in many respects, the late 20th century is a golden age of music -- though, living in the middle of it, we may have trouble perceiving this fact or distinguishing gold from its near imitations. Human nature (and the nature of music) being what it is, we must leave this perception to be developed in the early 21st century -- as always, just a little too late to do much good. In this, our time does not differ much from the age of Beethoven or Mozart.

The volume and pace of musical activity in recent years has reached levels unimagined in the past. There are undoubtedly more composers alive and working today than at any previous time. If we include popular music, there are certainly more composers alive today than in all past ages put together. Estimates on the quality of music being produced vary widely, and properly so -- de gustibus non est disputandum. But the quantity can be measured and it is amazing.

The quality of performance seems more subject to objective measurement than the quality of the music itself -- at least when the music is new -- and in this, the late 20th century is clearly a golden age of sorts. Performers of transcendent genius -- a Horowitz, Paganini, a Liszt, a Heifetz, Rachmaninoff or Casals -- cannot be produced on demand. They are the result of a happy interaction of heredity and environment; they arrive when destiny says they should, and mere humans can do nothing about it but hope and wait.

But competence -- that which can be taught and learned and systematically applied -- has never been at a higher level in music. The entrance auditions for our major conservatories are more demanding now than the graduation auditions were a generation or two ago. This may cause difficulties for aspiring young musicians, but it makes life better than ever for audiences. The competition for the spotlight is fierce among soloists -- would-be virtuosi -- and those who do not become the Paganinis of our time become superbly qualified, even overqualified, rank-and-file musicians.

The result is a significant enrichment of our musical life outside of the international jet set. Audiences have never had it better in terms of the technical quality of orchestras, the prevailing standards in free concerts and the qualifications of music teachers, who may be building an even more golden age just ahead.

Still, we tend to think of the past when the words "golden age" come to mind.

One such age, the second quarter of the 20th century, is distilled, embodied and documented in a new book-and-record package, "Virtuosi," just issued by the Smithsonian Collection of Recordings (LP Edition R 032 LCR-9265; seven records and a 160-page book; also available on five tape cassettes: 4X5L 9265). It is a more than worthy sequel and complement to the distinguished collections of jazz, pop and country music already issued by the Smithsonian.

The 30 selections range in date approximately from the beginning of the era of electrical recording to the birth of high fidelity. They are impeccably chosen and annotated by Richard Freed, and the Smithsonian's technicians have done a remarkable job of restoring the sound. The list of soloists (too long to present in full) is sheer magic. Casals, Landowska, Rubinstein, Heifetz, Lipatti, Kreisler are among the best known. Others, such as Dennis Brain, Leon Goossens, Alfred Cortot and Walter Gieseking, are equally worthy if not quite so widely recognized.

In the book, musicologist Peter Eliot Stone discusses the mystique and the history of the vituoso musician from classical antiquity to the present, with particular attention to such legendary figures as Liszt and Paganini. But these musicians can be presented only in words and pictures; the sounds packaged with the book are, necessarily, of more recent date.

Still, listening to these vintage performances -- Heifetz and Beecham in the Sibelius Violin Concerto, Brain in Mozart's Third Horn Concerto, Casals in a Bach suite and Piatigorsky in a Beethoven sonata -- one slowly drifts into a new idea of the meaning of "virtuoso."

In our time, it usually indicates someone who is eager to make the audience say "gee whiz" while keeping a deadpan, "shucks, it was nothing" attitude. In the calmer period between the wars, it seemed to mean, above all, a man in love with his music. That is the quality that emerges from these performances more than any other -- even from Heifetz, who became famous as a master of the deadpan style. There is an involvement that today seems to happen more often among the less-known musicians than among the virtuosi, who may feel that they are being paid to perform tricks -- the same tricks over and over again.

In these old recordings, you often get the feeling that the performer has lost himself completely -- abandoned all self-awareness -- in his concentration on what he is doing. Nothing that happens in music is more precious than this. And the very nature of the modern recording studio, with its orientation toward an artificial and ultimately uninteresting perfection, seems to counteract efforts toward such spontaneity.

There is also a kind of relaxation that is rare in the tensely competitive music scene of today. Some of these recordings were the first -- and for many years the only -- recorded versions of the music. The psychological atmosphere of the performance is therefore totally different. A musician taping the 10th or 20th recorded version of a concerto knows that he will be measured against others; that critics and music lovers can analyze his work through repeated hearings and compare it with any number of competitors. This knowledge cannot help affecting the quality of the performance, and the effect is not particularly positive.

All of this music is available in competing recordings that will sound better in purely physical terms. Whether they are better interpreted by later performers (who have the advantage of knowing and studying their predecessors) is something each listener must decide for himself. But this collection has a unique value not only for the extraordinary quality of music and interpretation it contains but even more for the way it allows us to slip, for a few hours, into the more relaxed and humane atmosphere of a bygone era.