An unfolding test of Metallica’s metal

Metallica has long seemed like some mighty leviathan of heavy metal, invulnerable to genre trends (unless they set them), the passage of time (their debut album “Kill ‘Em All� celebrates its 20th anniversary this year) and membership changes (the most recent exit: bassist Jason Newsted, in 2001).

But even this thunderous tank of a rock band now finds itself with health-related questions, and the answers start this week. Tuesday night, MTV will air “MTV Icon: Metallica,� a soundstage fete to the band that was taped this past weekend. Performers include the band itself as well as upstarts paying tribute (Korn, Avril Lavigne, Limp Bizkit among them).

Metallica joins only Janet Jackson and Aerosmith as honorees on the annual “Icon.� But they also go into the show with a lot of potentially unstable elements in their metal. For one, bassist Rob Trujillo (formerly of Suicidal Tendencies) debuts in the lineup and lead singer James Hetfield is making his highest-profile appearance since emerging from a rehab program.

Also, the band remains the Dixie Chicks of digital download with their fan-unpopular lawsuit against Napster (since dropped) and prominent soapbox.

More pressing to core fans, though, is the band’s new album, “St. Anger,� which reportedly goes to the hardest edge of the Metallica sound. Early word from the band’s label, Elektra Records, predicts an exciting listen for fans from the early days. “It’s back to this ridiculously hard edge,� one Elektra executive said. “No ballads, no guitar solos, just relentless and creative music.�

The CD is due in stores June 10. If a major success, it will be an especially welcome one for the band.

“There have been so many things in their band life lately and there is also a new musical direction with this album, so it is an interesting time,� said Long Paul, music director for KNAC.com, an online heavy metal hub.

The true proving ground for this band, as always, is the road, where Hetfield, drummer Lars Ulrich and guitarist Kirk Hammett have few rivals in power.

Their summer tour is shaping up to be one of the season’s blockbuster affairs, with red-hot Linkin Park on the bill and even Limp Bizkit, led by Fred Durst, who was a very public sniping rival to Ulrich during the Napster to-do.