Advisory to Metallica Fans: It’s a Pop Band Now : *** 1/2 METALLICA “Metallica” <i> Elektra</i> : <i> Albums are rated on a scale of one star (poor) to five (a classic). : </i>

For a couple of million kids, Metallica is the most important band in the world--and for the last six months, those fans have been worried.

Where Metallica had basically produced the previous albums themselves, the group went into the studio this time with Bob Rock, a producer best known for pulling slick, well-crafted, radio-friendly product out of Motley Crue, Bon Jovi and Kingdom Come, not exactly the sort of bands that get your average Metallica fan hot and bothered.

And despite the band’s careful spin control--inviting the editor of Rip magazine to sit in on recording sessions, jamming this year with every heavy-metal band that’s ever plugged into a stack of Marshalls and planning a Madison Square Garden listening party for 10,000 metalheads--the metal cult was still worried.

“Metallica” turns out to be a slick, well-crafted, radio-friendly album, as radical a departure from the symphonic scope of the band’s “ . . . And Justice for All” and “Master of Puppets” as, say, Dylan’s clangy “Bringing It All Back Home” in 1965 was from his earlier, acoustic stuff.

This is the album in which Metallica compresses its austere sensibility into a form palatable to the millions of people who would rather step into the path of a speeding truck than voluntarily listen to the new one from Cryptic Slaughter. And it might be as hard for a dedicated Metallica buff to come to terms with the band’s new sound as it was for hard-core folkheads when Dylan shifted to noisy electric guitars.

Has Metallica sold out? Well, only on its own terms. It takes a lot of chutzpah to risk alienating the biggest cult in rock ‘n’ roll.

Bob Dylan going electric is one thing--this is Metallica going pop.

For the first time, Metallica has hummable melodies, hooks, harmonies on the choruses, tight song structures like the ones on Guns N’ Roses tunes. Metallica’s riffs--rhythmic, precise monsters that had previously derived from drum rudiments--are suddenly based on the sloppy blues lick.

There are more prom ballads on this album than on the previous four combined; more bong-hit ‘70s stadium-style guitar solos; more moments when you can actually hear the bass. Where Metallica had stood alone at the apex of its genre, with an integrity and a purity of sound no other band approached, now it’s down in the trenches, with the Van Halens and the Motley Crues. And doing quite well.

Still, there’s a feeling that the band isn’t playing into its strengths--sense of space, alienation, compelling rhythms, crystalline beauty, awesome sterility of presence--and it seems as if it’s no longer in love with the possibilities of its sound. It’s as if, having lost the Grammy to Jethro Tull a couple of years ago, Metallica decided to become--well, not quite Jethro Tull, but maybe “Presence”-era Zep or something. “Metallica” has some genuinely catchy songs, even a hard-rock classic or two, but it’s been a hard album to get used to.