"But what about the kids?"

No matter where you are on Metallica's current tour -- backstage, at sound checks, on the tour bus, in hotel lobbies or most definitely, in hotel bars -- that is the question on everyone's mind. It's scrawled on almost all of the band's equipment cases, the last word usually spelled kidz. It's the standard Metallica response to every unavoidable road chore or promotional nuisance -- such as doing a press interview or making nice with the second cousin of a heavy local DJ who doesn't play the band's records anyway -- "But what about the kids?" someone inevitably groans.

But what about the kids? Well, they went berserko at the city hall in Sheffield, England, tonight. They pounded their fists on chairs, railings, walls and each other. They screamed themselves hoarse. And they kept up a two-hour orgy of head hanging and stage diving, looking less like a concert audience than a hurricane sea of denim, hair and black biker leather. While Metallica filled the smoky, sweaty air with its fierce thrash and lyric exhortations on death, disaster and heavy-metal brotherhood, the assembled teenage horde went ape. You have not lived the metal-concert experience until you've seen more than 2000 rock & roll animals bellowing in unison to Metallica's supersonic cover of "Last Caress," by the legendary punk gore hounds the Misfits: "I've got something to say/I killed your baby today!"

Now about a hundred of those animals are standing in the near-freezing cold outside the backstage door, hoping to get an autograph or at least to shake a hand when the band finishes toweling down and heads for the bus. Instead, "the kids" are all ushered inside, a dozen at a time to keep things orderly. They find the four members of Metallica -- singer-guitarist James Hetfield, guitarist Kirk Hammett, bassist Jason Newsted and drummer Lars Ulrich -- sitting at a table ready to give autographs, pose for photos and shoot the shit like normal every-day metalheads. They oblige their fans for the next hour and a half, signing everything thrust in front of them and listening intently to the fans' critiques of the evening's set. For Metallica, this is standard apr?s-gig operating procedure, as much a part of the evening as the show itself.

"I remember back when I stood outside for three hours waiting for autographs," says Hetfield later. "And when the star just hopped in his limo and took off, I'd think, 'You dick, I hate you.' I'd go home, rip down his posters. When there's a hundred kids outside, that don't bug me. They're there to see me. If they want my autograph, that's cool.

"We know where they're coming from," Hetfield says, because we've been there.

The phrase "But what about the kids?" is not a Metallica invention. Hetfield explains that the band's regular photographer, Ross Halfin, was on tour with Iron Maiden and that "he was telling one of their lighting guys, 'Hey, man, those red lights -- you gotta get rid of them. They look like shit in photos.' And the lighting guy says, 'But what about the kids? The kids need red lights!"

So Metallica gives 'em red lights, autographs and more, including one of the few truly raging stage shows making the 1988-89 arena rounds. It's a fair trade, too. Because it's the kids who have bought over a million copies of Metallica's latest album, . . . And Justice for All, zooming it straight into the Billboard Top Ten. And it was the kids who put the band's 1984 LP, Ride the Lightning, its 1986 LP, Master of Puppets, and its 1987 "covers" EP, Garage Days Re-Revisited, in the gold- and platinum-record winners' circles. It was the underground maniacs who were banging their heads to Metallica's legendary demo tapes and bazooka-metal LP debut, Kill 'Em All, back in '82 and '83, doing a word-of-mouth blitz on this killer California band that played everything faster than the speed of light and didn't put on any jive rock-star airs. It was the newcomers who saw Metallica's roaring bottom-of-the-hill sets last summer on the Monsters of Rock stadium tour and then bought more than enough Metallica gear at the merchandise stands to embarrass the headliners.