Spinal Rap

A few days before CB4 opens, Rock has taken refuge in the paper-strewn, dorm-room-like SNL office he shares with fellow cast member Adam Sandler.

''Hey! This is funny,'' he cries, riffling through a battered black-and-white composition book. It's filled with ideas for sketches he jotted down a few years ago. ''Found out my mother was not a virgin,'' he reads aloud. ''Wrong-camera theater: the show where everyone's looking in the wrong direction.''

When Rock joined SNL in 1990 after winning a small but loyal black following as a stand-up comic, his characters, most notably radical talk-show host Nat X, made a vivid impression. But lately he finds himself appearing ''less than once a show. My own mother doesn't watch anymore,'' he says, with a self-deprecating laugh. ''She's like, 'Call me when you're on.'''

According to SNL's producer, Lorne Michaels, ''People have historically gotten out of SNL what they've put into it. When Chris is focused and on his game, then he does great work. When he's distracted, he's less likely to do so.''

Rock, who is writing another film script with Boomerang director Reginald Hudlin, has no plans to leave SNL before his contract expires in 1995. But that has more to do with his past than with his prospects. His father, who juggled three jobs to support his wife and six sons, died four years ago; it is only now, as an adult, that Rock fully appreciates his dad's strict work ethic.

''I went through my 'trying to be hard' phase,'' he says. ''Hanging out on the corner, drinking Old English. It was stupid. My mother used to give me this speech all the time: 'You are not bad.' My older stepbrother's in jail. I think he shot somebody in the face. What the hell is his problem? He was trying to be hard.''

As a kid, Rock was bused to a mostly white Brooklyn neighborhood where he ''was called nigger every day''; he dropped out at 17 and got his GED. ''It was never like I was this dumb, can't-do kid,'' he says, balancing on his haunches in a swivel chair. ''But I never aspired to be anything but out of school. It would be really cool to do the whole five years here (at SNL). To graduate. That would really be cool.''

While he stresses, ''I really want to succeed on the show,'' CB4 is his attempt to regain the core black audience he fears he may be losing. ''It's kind of weird being the black guy on the white show,'' says Rock, who was the only black performer when he joined the SNLcast (there are now two others, Tim Meadows and Ellen Cleghorne). ''I'm not the hip black thing I used to be: You've got Def Comedy Jam, In Living Color, Martin. I just want to keep the street credibility, I never want to give that up. CB4 is just the film I need — it's the blackest thing I could possibly do.''