Heavy metal rock, such self-appointed experts as the organizers of the Parents Music Resource Center have informed us, is one of the most destructive cultural manifestations to grip the hemisphere since human sacrifice became passe'. How have the youth of America responded to this alarming bulletin?

Mo tley Cru e: 'Girls, Girls, Girls' Well, when the new album by L.A. metal provocateurs Mo tley Cru e entered the Billboard chart at No. 5 last week, it made the highest studio album debut since Stevie Wonder's "Hotter Than July" seven years ago, and four of the other records in the top six were by fellow metallurgists.

Such statistics don't tell the whole story, though. Chart-topping hard-rock bands like Bon Jovi don't play the caterwauling, antisocial metal that makes the PMRC particularly queasy -- their pounding power chords are frequently tempered by the keyboard riffs and backing vocals that make the sound acceptable to Top 40 radio. Even the bad boys of Mo tley Cru e have sheathed their iron hand in a velveteen glove this time out. "Girls, Girls, Girls" (Elektra 60725-1), in fact, sounds a little defensive.

Under the tutelage of former power-pop producer Tom Werman, the Cru e have attempted to broaden their reach. They salute Elvis with an adequate live version of "Jailhouse Rock," play some straightforward blues changes and even include a violin-drenched elegy for bassist Nicki Sixx's recently deceased grandmother (take that, defenders of the family!). None of the songs here is melodically well endowed, but most have a polished, radio-ready sound.

Lyrically, too, "Girls" often sounds like a bid for mainstream acceptance. The band members, who have publicly disapproved of substance abuse since lead singer Vince Neil was involved in a fatal DWI auto crash in 1984, have written two antidrug songs, though one, "Wild Side," sidesteps into an attack on the hypocrisy of politicians and other grown-ups. ("Papa won't be home tonight/ Found dead with his best friend's wife.")

There's one pleasure, however, the Cru e won't renounce: sex. They're quite fond of it, though their paeans to it are remarkably flat. The title song, a celebration of the band's favorite strip joints around the world, can muster only three appealing female physical attributes: "Long legs and burgundy lips," goes the list, "red lips, fingertips." (Maybe they thought "hips" was too easy a rhyme.)

"Girls, Girls, Girls" may live up to its No. 5 debut commercially, but the Cru e were better off as ignoble savages. The testosterone-fueled yelps of the band's early days weren't musically superior to their current work, but at least they had metal's essential ingredient, raw power. In cleaning up their act, the Cru e have just exposed how limited their skills -- especially their songwriting skills -- really are.

Heart: 'Bad Animals' Perhaps Mo tley Cru e will become reconciled to that weakness and seek professional help, as other rockers increasingly are doing. Beginning with the British Invasion, real rock bands (the Beatles) wrote their own songs; only ersatz ones (the Monkees) didn't. Recently, though, this has changed, with such venerable institutions as Starship enlisting ghost writers to guarantee hits. The new album from Heart, "Bad Animals" (Capitol PJ 12546), is the latest example of this phenomenon. Of the disc's 10 songs, only one was written without outside assistance.

When Heart debuted with the metallish 1975 hits "Crazy on You" and "Magic Man," it didn't need such support. A conventional hard-rock band with two twists, a woman lead singer and a lead guitarist who was the singer's little sister, Heart lost its way in the early '80s. Now, with outside material by such L.A. pros as Holly Knight and Billy Steinberg and a carefully constructed pop-metal style, the Seattle-based quintet has made a commercially impressive comeback.

"Bad Animals" doesn't make much of an impression musically, though. It's an archetypal soft-metal platter: The pounding drums, crunching guitars and melodramatic vocals are still there, but only as punctuation to the smooth, keyboard-dominated sound. (The title song is even built on a Philip Glass-like riff.) Nancy Wilson can still belt 'em out, but one can hardly blame her if she doesn't match the vigor of "Crazy on You." Prefab love songs don't inspire much passion.

Enthusiasm aside, the record is skillful work. Emphasizing ballads over rockers, it's bountifully supplied with catchy melodies, notably on the chugging "Who Will You Run To" and the tuneful "There's the Girl." The only thing the songwriting consultants couldn't provide is personality. Maybe real rock bands do have to write their own material.

Envy: 'Ain't It a Sin' Gina and Rhonni Stile write most of Envy's songs, though often in collaboration with their producer, Twisted Sister's Dee Snider. This New York quartet features a pair of sisters who sing and play lead guitar, respectively, but it has more than that in common with the Wilson sisters' group. It also wears its Heart, or rather the Heart of a decade ago, on its sleeve.

"Ain't It a Sin" (Atco 90605-1) is not a great debut record, and certainly not an original one, but it does have a freshness and sincerity the latest from Heart and the Cru e lack. Songs like "I See the Light (Let Me Rock and Roll)" are as formulaic as Gina Stile's trebly leads, but then part of Envy's appeal lies in its faithfulness to the form.

Real metal bands are dedicated to reproducing the sound just the way they first heard it. In fact, the PMRC may have more in common with metalheads than it realizes -- formally, metal is the most conservative of rock forms, something bands like Mo tley Cru e forget at their own peril. After all, there are always new traditionalists like Envy prepared to bang out the power chords their elders have forsaken.