THE WHO WERE back in town Saturday night, and if it seems as if they were just here, they were. Less than five months has elapsed since their last appearance here, a December 1979 show in which the veteran British band played in person to a capacity crowd at the International Amphitheatre while videotape simulcasts of the show took the action into a number of movie theaters. Most bands, obviously, wouldn't — couldn't — come back so quickly; the demand simply wouldn't be there again so soon. But the Who, just as obviously, is no ordinary band; Saturday night once again found the Amphitheatre sold out for a show that was basically a repetition of December's superb performance — with a few notable differences.

Like lead guitarist Peter Townshend's beard, which disappeared sometime between the band's '79 show here and now, the Who's ambitious set has undergone some definite pruning. The keyboard player augmenting the quartet on their last year's tour remains, but the three-man horn section has been dropped, and the show has been shortened considerably from its original 2 1/2 hours. Instead of doing the whole show themselves, the band now tours with an opening act, which makes the whole affair seem less like the special event it did last time around.

Given the fact that last time around marked the band's first U.S. tour in nearly four years and their first with new drummer Kenny Jones replacing the wildly distinctive Keith Moon, things were bound to seem a trifle anticlimactic the second time around. Coming so quickly on the heels of their '79 show, such comparisons are inevitable; but taken solely on its own merits, Saturday night's show was extraordinary enough — the sort of thing that for the Who seems to amount to business as usual. Among the classiest of live acts in terms of both expertise demonstrated and energy generated, the Who at their best can be one of the most exhiliarating experiences rock has to offer.

THE WHO'S IS a show fairly short on special effects. Flashpots burst into flame as lead singer Roger Daltrey winds up "Won't Get Fooled Again," the band's name is spelled out in lights at the finale, and that's it. And while Daltrey's by now familiar trick of tossing and catching the microphone and Townshend's windmill guitar style add considerable visual appeal, it's the energy in the music that makes the band so special.

Saturday's set covered much of the band's history, from the late '60s hit "I Can See for Miles" to "Who Are You," the title track from their most recent studio album. As always seems to be the case, however, it was the songs from "Tommy" that got the biggest response — along with "My Generation," the Who's "youth anthem" of 1965. Fifteen years later, it still remains relevant — as do the Who.

Rock band Blackfoot turned in a decent enough performance as opening act, a fairly thankless task given the fact that the audience was hot for the Who. The band's performance has improved a good deal since I saw them last year at the Aragon, although maybe it has something to do with the respective sound systems. While the Amphitheatre isn't the greatest place for concerts in terms of acoustics, the sound quality Saturday was miraculously good.