The World of Hard Rap : CHECK LIST****<i> Great Balls of Fire</i> ***<i> Good Vibrations</i> **<i> Maybe Baby</i> *<i> Running on Empty </i>

*** BIG DADDY KANE. “Long Live the Kane.” Cold Chillin’/Warner Bros.

** BIZ MARKIE. “Goin’ Off.” Cold Chillin’/Warner Bros.

*** 1/2 EPMD. “Strictly Business.” Fresh.

*** TRUE MATHEMATICS. “True Mathematics Greatest Hits.” Select.

** 1/2 SCHOOLLY D. “Smoke Some Kill.” Zomba/Jive/RCA.

* 2 LIVE CREW. “Move Somethin’.” Luke Skywalker.

Welcome to the topsy-turvy world of hip-hop, where guys you’ve never heard of sell more records than Motley Crue, producers are more acclaimed for the beats they rip off than for those they create, and the nicest thing you could ever do for a rapper is to call his music hard : raw, unpalatable, completely uncommercial. Hard rap records occupy roughly the same niche in black music that heavy metal does in rock, and the very slickness of, say, Run-D.M.C.’s last record, is anathema to the core hip-hop audience.

A 15-year-old rapper can make a cheap demo tape in a friend’s garage one afternoon and have it become a club hit a couple of weeks later. An unemployed Compton kid with no experience in the industry can create a record empire in a few months. KDAY (1580 AM), the premier L.A. hip-hop station, has records in steady rotation--good records--that sound as if they were mastered off the producers’ answering machines.

With major record companies tripping over themselves recently to acquire tiny independent labels, such previously obscure acts as Boogie Down Productions and Jazzy Jeff & the Fresh Prince made truly great rap albums that vaulted them into the front ranks. And for the first time, almost every second-tier rapper put out not just 12-inch singles but full LPs.

Warner Bros. picked up Cold Chillin’, a label based around the considerable talents of Marley Marl, a master-mixer who has nurtured an entire generation of Queens rappers. At their best, Marl’s productions have an eerie, nervous edge, a twitchy moodiness sometimes closer to “serious” music by people like Harold Budd than to the street. When he scratches, the grooves wail with grief.

Marl’s best production so far is “Long Live the Kane” by Big Daddy Kane, whose tough, smart rhymes and head-cold machine-gun articulation are set off well by Marl’s modalities and spare, shuffling beats. “Ain’t No Half Steppin’,” the cut you’ve heard on the radio if you listen to this stuff, is dense and mournful, with a strange, tinkly piano motif cutting over and over again through the mix. “Raw” approaches the top-rank chill intensity of the Public Enemy Armageddon groove. Even routine tracks are shot through with eerie, broken-record moans.

Marl’s arty approach works much less well with good-time party rapper Biz Markie, whose “Goin’ Off” is a ragtag collection of old 12-inch singles, goony brags and one genuine hit: “Vapors,” a sweetly naive number about the simple pleasures of Schadenfreude. Biz delights in dumb rhymes, and the production just overwhelms them. What can you say about an album whose best track is called “Pickin’ Boogers”?

The king of dumb rappers is Philadelphia’s Schoolly D., who is beloved by Europeans and (white) East Coast critics for the violence of his lyrics, from which they get some sort of an anthropological frisson . A lot of rap cognoscenti suspect his first album--all about the pleasures of gang membership, guns and smoking something called “chiba”--was a goof. His new one, “Smoke Some Kill,” is hardly less goofy, a dirty-lyric paean to drugs and fat gold chains on which a song called “No More Rock N’ Roll” follows one based on Led Zeppelin riffs. The beats are hard, and the thing is as funny as a Redd Foxx routine.

No less a liberal than Dave Marsh has suggested that if censorship has to start somewhere, it might as well start with the 2 Live Crew’s “Move Somethin’.” I agree. The Miamians’ backing tracks are watered-down, speeded-up versions of stuff you’ve heard a million times on Power 106. The rhymes are witless pre-adolescent naughty-wordplay. You can’t dance to it, either.

You can dance to the clean-cut, collegiate rap of Long Island’s True Mathematics, who thank no fewer than 10 fraternities and sororities on the jacket of their ingeniously named first record. “True Mathematics Greatest Hits” has a feel not unlike the loose, warped ‘70s-funk groove of PE’s first album. The rapping is reminiscent of a laid-back L. L. Cool J, the attitude that of the rapper-next-door.

And Long Island’s EPMD is hip-hop’s dance band of the year: sampled grooves infinitely repeated from your ears down to your feet and as hard to resist swaying to as the Time were in their heyday. “Strictly Business,” filler-less, rules party turntables because it transforms the room unobtrusively, like a brilliant friend you like to hang out with because he makes you feel smart. Hard never felt so good.