THE SEVENTIES have been rough on the great rock bands of the sixties. The Stones stopped rolling, falling in to a stultifying disco beat; the Grateful Dead waxed and waned depending on the quality of their high; the Jefferson Airplane took off for the stars, finding commercial success but artistic failure. The Beatles, of course, never made it into this decade, and individually they've only embarrassed themselves and us. Here in 1978, the old jokes about aging rockers just don't seem funny anymore.

Nonetheless, those convinced that senescence is a legitimate excuse for the decay of rock talent should listen to Who Are You and think again. The most inspired, exciting album in a long while comes to you not from the latest New Wave band to slouch out of CBGBs, but from the nearly middle-aged group that sang "My Generation" 14 years ago.

Yes, the nasal chorus that backs lead singer Roger Daltrey on most of Who Are You hasn't changed very much since the days when the band dressed up in Union Jacks. It's striking how little else has changed. The Who's sound has remained consistent longer than most groups have remained together.

While other rock groups got lost in a technological doldrums which enervated their music, the Who--masterminded by Peter Townshend--stuck to the basic rock style of the sixties. Today, the financially strapped old-timers and the lobotomized New Wavers backtrack towards their roots, only to find the Who have been there all along, not stagnating but maturing, gaining depth, growing subtle.

Subtle hard rock? Most groups that sought it, like Yes and Genesis, vnthesized the rock right out of their music. Townshend's use of the synthesizer has always been comparatively restrained; if he never explored new frontiers, neither did he emasculate his group's music. This approach pays off on Who Are You, in songs like "The Music Must Change," a thriller in which the sound swells like an electronic tide rising and falling behind the rhythym section.

The depth and density of the music insures against mindlessness; we can be certain the Who will never produce mechanical monotonies like the Stones' "Hot Stuff" and "Miss You." Indeed, "Sister Disco," a Townshend song on the album, lets us know exactly where the who stand:

Goodbye, Sister Disco,

With your flashing tramp lamps

Goodbye, Sister Disco,

And to your clubs and your tramps.

A synthesized, speeded-up parody of a hack disco string section follows.

Though Townshend remains the Who's musical standard-bearer, it's clear that the other members are now full partners. John Entwistle, the bass player, wrote a full third of the album's nine songs, and they're every bit as good as Townshend's. "905," a song about a depersonalized future, has a cold, catchy beat recognizably not Townshend's but definitely the Who's. Daltrey has once again taken control of his voice and uses it with as much energy as in the past, and more dramatic flair, controlling the frenzy and leaving the primal screams for a few climactic moments.

THE APPARENT new unity of the band makes the recent death of drummer Keith Moon that much more tragic. Moon was always best known as the scourge of hotel managers across the world, but he was also one of the few rock drummers with a distinctive style--a feverish, restless beat that must have reflected his self-consuming way of life.

The lyrics on Who Are You are as hard-bitten as ever--only the Who would produce two different songs with the title "I've Had Enough." The newer one (the first was on Quadrophenia) reads like an update of "We Won't Get Fooled Again," but the words are even more desperate, the music unsettlingly ambiguous.

This pessimism prompts lines like: