MUCH OF THE APPEAL of heavy metal is a matter of musical muscle, aggression carefully channeled into crunching power-riffs and a bone-crushing beat. Trouble is, metal's dependence on sonic shrapnel cuts two ways. Without it, a band simply sounds wimpy; add too much and the group ends up too uncommercial for mass market acceptance.

The most obvious solution would be to hunt for a middle ground, but that's a lot easier said than done, especially given the decreasing tolerance of radio and video for heavy metal in general.

By rights, Judas Priest ought to be immune to such pressure. For one thing, the band has never sought the sort of validation brought by top 40 singles; for another, its sound so perfectly distills the Gothic glamor of classic British metal that additional hooks somehow seemed superfluous. Nonetheless, "Turbo Lover," the band's latest, seems surprisingly attuned to the chemistry of Contemporary Hit Radio.

That's not to say the band has sold out, for there is crunch aplenty here, from the high-torque title tune to the relentless riff-rocker "Wild Nights, Hot and Crazy Days." But the band has been careful to cram extra melody and harmonies into each song, where once mere musical muscle would have sufficed. That's not so bad when left to the likes of "Rock You All Around the World," but when paired with the pat protest of "Parental Guidance," it leaves Judas Priest seeming too calculating for comfort.

Still, that's better than Dokken does with "Under Lock and Key," an utterly unconvincing piece of heavy metal posturing. True, frontman Don Dokken has one of the most expressive voices on the California heavy metal scene, and the production team of Neil Kernon and Michael Wagener has given the band power and presence to spare.

But plumping each chorus with extra vocal harmonies and carefully compressed power chords doesn't quite make up for missing hooks and lame melodies. And that's what ultimately keeps Dokken from rockin'.

JUDAS PRIEST -- "Turbo Lover" (Columbia 06 40158);

DOKKEN -- "Under Lock and Key" (Elektra 9 60458); both appearing Saturday at the Capital Centre.