It is one of the more curious musical anomalies of this century that Mahler's electrifying Sixth Symphony, which the Cleveland Orchestra played last night under Lorin Maazel at the Kennedy Center, should enjoy its present commanding popularity with conductors, orchestras and audiences alike.

The work was alone on the program. The house was packed; the Clevelanders were performing to their fabulous hilt, and Maazel conducted with a degree of emotional involvement quite different from his sometimes dry, austere style. In other words it was a triumph.

The Sixth is one of Mahler's grandest creations. Where some of his work, for all is beauties, can occasionally ramble and seem overstated, the Sixth, for all its hour-and-20-minute length, is concise, sharply focused and all of a piece. There is less of the hysteria so characteristic of the composer. And, even though it is in a minor key and dubbed the "tragic," the real musical crux of the work is the ambivalence between the joy of the major key and the sadness of the minor.

But until recently virtually no one would have known that. The symphony was not even performed in this country until 1947, 41 years after its composition, when it was introduced by Dimitri Mitropoulos. But once it became known, the Sixth shot quickly to the enormous renown it now enjoys, and presumably will continue to enjoy. Last night's wonderful performance and the standing ovation that followed would seem to insure that.