JOHANN SEBASTIAN BACH, born 300 years ago today, is as near as your stereo set, his face on T-shirts and coffee mugs, his music more widely heard than ever. Yet he is also as distant as the century in which he was born.

A while back the flamboyant organist Virgil Fox was giving one of his popular concerts for people who had come to music primarily through rock 'n' roll. Those things tended to be spirited celebrations of Bach -- the late Mr. Fox was one of his most ebullient interpreters -- calling for a certain amount of audience participation. After a couple of bouncy fugues, Mr. Fox changed gears. His next selection, he announced, would be an organ prelude to a cantata entitled, "Behold, I Stand With One Foot in the Grave." The reaction from the audience was telling: a second of silence followed by a ripple of nervous laughter. It was a reminder of the distance that separates us from the time and place in which Bach lived. A choral work whose sentiments must have seemed quite natural to congregations in the early 18th century causes uneasiness among celebrants in the late 20th.

Last Sunday a series of long lost Bach organ compositions, recently discovered in a Yale University library, was performed in a special concert at Yale. They were preludes to hymns, and there was in them, Lon Tuck wrote in a review in The Post, "that overwhelming sense of majesty, of something mightier than one's own self, that is the essence of Bach's organ music at its greatest." Soon they'll probably be played not only on church organs but on stereo sets -- sometimes listened to and sometimes serving as background for conversations on the benefits of racquetball and the prices of Italian wines.

How would Bach have reacted? Well, we wouldn't be surprised if he walkedinto the room, sat down and started listening intently to see whether the organist was getting it right. For while it's true that he was a religious man in a religious age, he was also an extraordinarily dedicated and hard-working musician -- a perfectionist both as performer and composer, a serious student of the works of his contemporaries and of those who had gone before him.

Much of his music was religious, but much was also secular. Not all of it was appreciated in his time, and some of it was called old-fashioned. Some of it sounds to us today as if it came from the future rather than the past. So Bach is, at least to some extent, a figure of our time also, and one to celebrate in this tercentenary week.