IT MAY SEEM like splitting hairs to some listeners but there is a difference between hard rock and heavy metal. Granted, both are loud, brutishly simple and guitar- obsessed. But where heavy metal tries to grind that down to a fairly narrow formula, hard rock uses the same sounds to batter the barricades of pop. Here are are some current hard rock albums:

AEROSMITH -- "Done With Mirrors" (Geffen GHS 24091). Although this reunion album is clearly the band's best in years, it's going to take more than the original lineup to put this band -- at the Capital Centre this Friday night -- back in the saddle again. The instrumental interplay is as sharp as ever, but aside from the Joe Perry oldie, "Let the Music Do the Talking," the writing lacks the bite of the back catalogue.

TED NUGENT -- "Little Miss Dangerous" (Atlantic 7 81632-1). Nugent, who will be opening for Aerosmith this Friday, hasn't exactly lit up the charts lately, either, but this ought to bolster his sales some. The material is classic Nugent, full of sex-crazed girlfriends and gonzo guitar breaks, and producer Pete Solley does his best to add bite to the Motor City Madman's sound. But the real difference seems to be the Nuge himself, whose brash enthusiasm infects the music with an almost irresistible energy.

THE FIRM -- "Mean Business" (Atlantic 7 81628-1-E). Between them, Jimmy Page and Paul Rodgers ought to epitomize all that was worthy in early '70s hard rock. Why, then, does The Firm (slated to appear at the Capital Centre March 19) seem so intent on reminding us of how pompous it all was? Granted, it doesn't help that drummer Chris Slade plays as though he's about to put in for early retirement, but it would take more than vigorous propulsion to enliven the likes of "Spirit of Love" or "All the King's Horses."

BLUE OYSTER CULT -- "Club Ninja" (Columbia FC 39979). As the band's lineup slowly erodes, Blue Oyster Cult seems more like a studio concept than an actual band. How else to explain the overriding anonymity of the instrumental track here? The irony of it all is that at times the lyrics, courtesy of Jim Carroll and Eric von Lustbader, among others, are among the band's best in years. That is, so long as you exclude "Make Rock Not War."

PETER FRAMPTON -- "Premonition" (Atlantic 7 81290-1). No pretty boy ballads here. Instead, Frampton works hard at honing his sound, updating the bluesy grit he had with Humble Pie while still keeping an eye on the pop side of things. That works reasonably well with "Lying." But elsewhere, the distance between Frampton's blues- drenched guitar and his feckless English accent seems almost insurmountable.