BACH'S "Goldberg" Variations enclose the career of Glenn Gould like a pair of parentheses. They were the first music he recorded in 1956, and his new interpretation of the same work -- just issued and already unobtainable in several local record stores -- was the last recording issued before his death.

If Gould had wanted to summarize his life's work in one piece of music, he might well have picked the "Goldbergs," which have been given that role anyway by his untimely death. In this elaborately ornamented little tune with 30 variations, Bach created a self-contained and incredibly diverse world -- "to delight the hearts of music-lovers," as he said on the title page of the first edition. The sheer brilliance and variety of invention in the music is unmatched by any other set of keyboard variations except perhaps Beethoven's "Diabelli." It was ideal music to make Gould an international star, as it did almost overnight when he first recorded it in 1956. And now it is the ideal music to round out the story of his remarkable career.

In two words, that story -- as embodied in the two recordings of the "Goldbergs" -- is one of continuing growth. The young Gould was brilliant, not merely as a pianist but as a musical thinker. The 1982 Gould retained that brilliance and added a depth of nuance, a sensitivity to expression and the music's overall structure that shows the young virtuoso fully matured.

It is reported that Gould planned to stop recording music entirely after his 50th birthday, as he stopped performing in public abruptly in 1964, and that he felt he had already recorded all the music he found worth the effort. Without questioning his taste -- to which he was certainly entitled -- I would suggest, after hearing his new "Goldbergs," that he should have returned to some of his earliest recordings and taped new interpretations. The performances are different enough, and the differences interesting and exciting enough, to justify duplication.

The most obvious difference in the new version is that it gives the listener more music in terms of playing-time. This is not only because the mature Gould is more interested in observing Bach's repeat marks but because he is less interested in breaking speed records at the expense of expression. At 24, Gould was technically brilliant -- that is to say, fast and accurate. He could articulate an amazing number of notes per second without losing any clarity, keeping the voices fully distinct even in the trickiest passages of counterpoint. His 1956 record stands as a permanent and amazing monument to that ability.

In 1982, Gould is more often inclined to linger fondly over a phrase and probe its expressive possibilities and to accent this music, as it must be done on the harpsichord, with little tricks of timing -- microscopic pauses or little rushes between one note and the next. And these subtleties are more effective if sheer speed is not the primary consideration. Sometimes the differences in speed are not all that drastic. The 1982 Gould is about five seconds slower, for example, in the precipitous Variation 14 (the one with those cascades of three-note figures in measures 9 through 12 and 25 through 28), which lasts about a minute in the new recording. But the difference in effect is striking.

Also striking is the sense of overall architecture in the new interpretation. As in 1956, each of the 30 variations is given a distinctive character, but they fit together in larger structures more clearly than before. Particularly impressive (although it is only one example among many) is the crescendo of brilliance in the last few variations (following a lyric reading of No. 25 that might make one think of Chopin) that leads into a simple and hauntingly beautiful final statement of the original theme.

But whatever virtues the new performance has, they do not nullify those of the earlier version, which remains what it has been for more than a quarter-century--one of the most dazzling keyboard performances on records. In a way, the new version enhances the value of the old by putting it in perspective and documenting the artist's growth from the beginning to the end of his career. If it is wise, CBS will keep both versions (properly labeled) in its active catalogue -- but one cannot always expect record companies to behave wisely. CBS has been quite good, on the whole, about keeping Gould in circulation -- no doubt because the record-buying public has continued to be interested. But his Schoenberg recordings -- the complete piano music and the songs for voice and piano -- have dropped out of sight along with the complete Schoenberg set in which they were contained. I plan to replace my copy of the 1956 "Goldbergs" (which is somewhat the worse for wear) while I am still sure it is possible, and I would advise other Gould devotees to do likewise.