MUSIC; Rappers Who Definitely Know How to Rock

WHEN Run-DMC and Aerosmith teamed up for ''Walk This Way'' in 1986, the result was a culture clash -- and a huge success. Critics and fans alike were captivated by the spectacle of upstart black rappers alongside veteran white rockers, and the music video played up the contrast: Run-DMC, clad in its trademark black jeans and sweatshirts, greeted the long-haired Aerosmith first with anger, then with enthusiasm. The song established Run-DMC as crossover pop stars and revivified Aerosmith's stagnant career. The Rev. Dr. Martin Luther King Jr.'s integrationist dream had returned as a brilliant marketing scheme.

Nearly 15 years later, such pop integration is more lucrative than ever. This fall, the rap-rock group Limp Bizkit broke sales records with its hugely popular third album, ''Chocolate Starfish and the Hot Dog Flavored Water.'' And there's more where that came from: rock bands from Sugar Ray to Rage Against the Machine have figured out that simple riffs and simple rhymes sell records. But all this mixing and matching doesn't necessarily create a radical cross-cultural pop utopia. In the first place, the old notion of rap-rock as racial harmony doesn't quite hold up in an age in which the most important rapper is an angry blond named Eminem. More important, the music doesn't sound as fresh as it once did: the riffs-and-rhymes formula that powered ''Walk This Way'' remains the blueprint for most rap-rock.

So is rap-rock played out? Well, no. In the last few months, three new albums have suggested fresh variations on a not-so-fresh theme. As it happens, all three come from the world of hip-hop, from acts that aren't usually mentioned when rap-rock is discussed. OutKast, Mystikal and M.O.P. are unlikely saviors for a subgenre ruled by heavy-metal heroes like Limp Bizkit. Rap-rock usually means rockers ripping off rappers, not the other way around -- more ''Headbanger's Ball'' than ''Player's Ball.'' These three new albums are exhilarating evidence of what can happen when rappers turn the tables.

The Atlanta-based hip-hop duo OutKast has always been too uncategorizable to be considered rap-rockers. In the course of three exquisite albums, Big Boi and Andre 3000 have made some of the best pop music of the 90's, tackling Southern soul music and space-age beats with the same hyperliterary glee. But a recent performance in New York City found OutKast in full rock 'n' roll mode: Big Boi's straightened hair hung down to his neck, his rhymes nearly drowned out by a pair of electric guitars. Indeed, electric guitars are everywhere on the group's fourth album, ''Stankonia,'' which draws inspiration from funk-rock guitar gods like Jimi Hendrix, Sly Stone, Prince and Eddie Hazel of Funkadelic. In the process, OutKast has created an album -- and a live show -- that is looser and more inventive than the usual rap-metal bombast. Tracks like ''Gasoline Dreams,'' ''B.O.B. (Bombs Over Baghdad)'' and ''Slum Beautiful'' feature guitars bubbling in and out of the mix, and it's often hard to tell the live instruments from the electronics.

By invoking an often overlooked history of black rock, OutKast collapses the rap-rock dichotomy that groups like Limp Bizkit take for granted. On ''Chocolate Starfish,'' listeners can choose between a rock song called ''Rollin' (Air Raid Vehicle)'' and a rap song called ''Rollin' (Urban Assault Vehicle)''; Limp Bizkits treats the two genres as an either-or proposition. OutKast, on the other hand, sees rap and rock as kindred spirits that are more or less inseparable. On planet Stankonia, rock and rap are twin traditions bringing an earthy aroma to an alien landscape.

Of course, rap-rock is about more than just loud guitars. It's also about screaming: on ''Chocolate Starfish,'' the frontman Fred Durst is at his best when he's roaring. But his vaguely monstrous vocals aren't as far removed from the world of hip-hop as one might think. He has a counterpart in Mystikal, a New Orleans-based rapper whose wild-eyed delivery makes the well-known hip-hop loudmouth Busta Rhymes sound positively serene.

Mystikal, a Persian Gulf war veteran who rose to prominence as a protege of the rap impresario Master P, struck out on his own in September, with a charged-up album called ''Let's Get Ready.'' The hit single ''Shake It Fast'' combines Mystikal's full-throttle vocals with a catchy little ditty celebrating the female backside. On the rest of the album, Mystikal goes from a conspiratorial whisper to a vein-popping scream in the course of a few words, and he's constantly accelerating and decelerating his delivery. The sound is new, but it's not unprecedented: one can't listen to Mystikal without being reminded of R-and-B screamers like Little Richard, Screamin' Jay Hawkins and James Brown. On the song ''I Rock, I Roll,'' Mystikal makes the connection more explicit, using piano and saxophone sounds to underscore the common history of rock and rhythm-and-blues.

When emulating 1950's rock pioneers, Mystikal casts contemporary rap-rock screamers in a whole new light, reaching back to the roots of rock to create something that sounds both utterly maniacal and startlingly traditional. Unlike Limp Bizkit's singleminded new album, which often drifts into noisy monotony, ''Let's Get Ready'' shows just how suggestive an ear-splitting scream can be.

It should come as no surprise that the best rap-rock doesn't always find the top of the charts; when it comes to popular culture, marketing and timing often trump artistic achievement. Nevertheless, the story of the Brooklyn-based group M.O.P. is striking: in 1997, it released a hard-rock EP called ''Handle Ur Bizness,'' which hit stores about a year too early to capitalize on the rap-rock boom. The duo of Lil' Fame and Billy Danze had made a name for themselves as rowdy hip-hop traditionalists, and their fierce, simple rhyme style seemed perfectly suited for a heavy-metal crossover. But ''Handle Ur Bizness'' didn't much impress critics or listeners, and the subsequent album sounded unexpectedly flat.

This fall, M.O.P. returned to form with ''Warriorz,'' a thrilling, stripped-down collection of songs powered by sampled beats that mimic the bold simplicity of hard-rock guitar riffs. ''Warriorz'' doesn't sound much like ''Handle Ur Bizness'' -- the group samples everything from old jazz records to the soundtrack from the movie ''Carrie'' -- but M.O.P. hasn't entirely abandoned rap-rock.

In fact, ''Warriorz'' contains the year's most exciting (and most unlikely) rap-rock single, a song called ''Cold as Ice.'' If the title sounds familiar, it should: M.O.P. reworks the 1977 song by the much-maligned hard-rock balladeers Foreigner. The rappers use only a brief sample of the original, replaying Foreigner's classic couplet at double-speed: ''You're as cold as ice/ Willing to sacrifice.'' While too many rap-rock acts are content to appropriate musical traditions without much changing them, M.O.P. embraces the transformative potential of sampling, turning the singer Lou Gramm of Foreigner into an R-and-B diva. Add a tremendous bass line and boisterous lyrics threatening physical harm, and suddenly Foreigner and M.O.P. sound as if they're in cahoots: ''Stop him if you could (You're as cold as ice)/ And you'll be stiff as a log, in a suit, looking nice.''

The bottom line is that rap and rock aren't as different as they sometimes appear. In fact, hip-hop's rock envy stretches back to the late 1970's, when pioneers like Grandmaster Flash and Kool DJ Herc chopped up records by everyone from James Brown to AC/DC, proving that a heavy guitar line could be just as effective as a funky bass line. Back then, rap's fondness for sampling and stealing seemed like a weakness; it was easy to disdain songs built from bits of other songs. But over the years, this tradition of shameless appropriation has turned out to be hip-hop's greatest strength: it's an anti-traditional tradition, and it ensures that almost every rap album contains a few surprises. From the outside, the hip-hop world may seem impregnable, hermetic, but these three albums reveal a different story: they suggest a world where no form of popular music is out of bounds.

Indeed, by looting rock music the way they loot everything else, OutKast, Mystikal and M.O.P. raise a tantalizing possibility: that rap-rock -- and perhaps rock 'n' roll itself -- isn't quite as lifeless as it often seems. By repositioning rock 'n' roll in the broader context of popular music, all three groups set it free, making rock sound the way it was always supposed to sound: youthful, energetic and utterly unpredictable.