The Who defrosted a Coliseumful of quick-frozen pop freaks Wednesday evening and fished up a mess of parboiled, panfried and oven-baked rock ’n’ roll.

Why did they do that? To prove that unlike the other crack outfits of the initial American invasion by British rock — the Beatles, now disbanded, and the Rolling Stones, somewhat atrophied — The Who not only packs ’em in like Elvis but is still hungry for new instrumental tastes and theatrical savors.

Which brings us to “how.”

How they didn’t do it was painfully dramatized by Bell and Ark, a little-known rock quartet which at this point richly deserves its ample obscurity. Lone warmup group on the over three and a half-hour show, B and A occupied itself and perhaps even part of the audience with spaniel-like mimicry of Joe Cocker — contortions, vocal inflections and all — corrupted Bob Dylan and repeated ripoffs of the amp guitar wow sounds utilized by Isaac Hayes in his score for the movie “Shaft.”

After a tediously long intermission, during which technicians failed to anticipate all the bugaboos in a jungle of equipment, The Who crept onto a darkened stage and blasted off in a blinding prism of light provided by 36 — count ’em — onstage red, blue, green and yellow spots blended to magenta, fuchsia and cerise by pink and mauve gels on the massive Coliseum ceiling spots, each of which hugged one of the four superstars like a man covering a pass receiver.

But appearancewise, it was a new Who. Already long gone was lead guitarist Peter Townshend’s Union Jack jacket, replaced now by various but always white stage clothes. But gone too are the long haircuts and the machinegun guitar routines.

Despite electric feedback and mikes cutting out, The Who managed to stage a wild exercise in participatory media, less concentratedly musical than theatrical.

Surprisingly reticent in his rare solo choruses, Townshend, the celebrated guitarist opted for Townshend the mastermind of a powerful pop culture happening.

Bouncing about the stage adjusting sound levels, tuning his guitar and synchronizing licks with tambourines and taped Moog synthesizer patterns, Townshend wound psychic musical springs tighter and tighter with his flailing arms, sent colleagues toppling with his abandoned gestures of pure surprise and embellished long bouts of British boogie with leaps, kicks and crouches, at times whooping and dancing war like some crazed old rock ’n’ roll chieftain.

For his part, lead singer Roger Daltry pumped away on a close-to-the-floor mouth harp, hopped and crooned animatedly and constantly twirled his hand mike by its cord like a wildly elongated marshmallow yo-yo.

Churning through a few of its own oldies like “Pinball Wizard” and the more familiar parts of the group’s rock opera “Tommy,” as well as perennials like Eddie Cochran’s “Summertime Blues,” The Who focused chiefly on its later recorded works such as “Behind the Lines,” “Robert Hall Bargain” and “Barbara Riley.”

But even in its instant replays of earlier hits, The Who found new patterns to run and unfamiliar strategems to develop, heading its music toward a neurotic but wildly fluid form of theatrical spontaneity.

Its overhaul of “Magic Bus” from the early album "The Who on Tour” becomes with its new chassis a dizzily careening charabanc ride into the fantasy land of the British moors, poltergeists prancing at every portal and druids and mountebanks lurking at every turn. But the bus, as on all Who trips, bounces like crazy.

Near the close of the show, Townshend glanced downward and shrieked disbelievingly, “My God, we’re playing on carpet!” — as though they’d rolled one out especially for The Who.

They had.