Poor Jeff Cole. Been under so long it looks like over to him.

Cole (Omar Epps) is by profession a narcotics detective. His job is to penetrate the thug life by pretending to be a thug and thereby get the goods on the true thugs. It's clearly a job of acting, except that in this case, the critics carry Glocks. One slip and he ends up floating across the Ohio River (the setting is Cincinnati) to Kentucky. So he has to become the world's best method actor or the world's deadest narc.

That's the gist of "In Too Deep." The young policeman has to become an invented character named J. Reid, an Akron dealer moved up to the big time in Cincinnati. As it turns out, Cole has talent; he can become this other man, he can even flourish in the environment. His gift isn't courage, or not entirely courage: It's conviction. He becomes what he believes, and it's the force of that belief that keeps him alive.

The movie, directed by Australian Michael Rymer, has a gritty authenticity to it and captures the bleakly cold look of Ohio in late winter, when the snow has turned to muddy slush and the trees are bare and everywhere you look you see damp, cold darkness. It also captures the spectacular crazed quality of urban violence, far from the syncopated choreography of the Hollywood product but much more like pie fights with guns, messy and squalid and permanent. But it's about what's under the surface, where fear and doubt eat the soul and where you have to commit to a style and, once that commitment is made, hew to it with every morsel of your imagination.

This hasn't always been the case. I'm remembering other undercover men in movie history. In "White Heat," Edmond O'Brien plays a lawman who penetrates Jimmy Cagney's screwball gang of armed robbers. It's easy for O'Brien, because Cagney's Cody Jarrett is such a screaming bull goose nut case, the detective never loses his bearings. Cole has another problem: It's that the man he's set to bring down turns out to be someone he comes to like.

His target is LL Cool J as Dwayne Gittens, a k a "God." God is the power on the streets of the river town; the police think he's tied to 80 percent of the crime in the city. It's the genius of "In Too Deep" that God is the most attractive character in the film, for that really is the nature of human evil. The evil man, being without doubts and restraints, is also the most free, which confers enormous charisma. His lack of fear may be psychotically based, but it feels like swagger and bravado and leadership. His willingness to punish feels like confidence. His slipperiness with the language, always finding a way to pass the blame, feels like eloquence. He's the scariest thing out there: bad guy as natural-born stud.

The fact that LL himself is, under the performance, an extremely likable man with natural charisma is the key to the movie's edge. The more attractive is God, the higher the stakes for Cole, and therefore the more intriguing is the film.

The movie also seems to have its anthropology right. I am no expert, but as an account of life on mean streets, and the attendant language of those streets, "In Too Deep" feels spot on. I like the way Cole's J. Reid rises quickly in the gang, because he has fast hands and can stay with God in sparring exercises, where the others can't. That makes sense. The writers, Michael Henry Brown and Paul Aaron, have thought about what is valued in that culture and build their movie around sound insights like that one.

Other features are less admirable. A love affair, between Cole and a dancer played by Nia Long, feels quite routine, except one scene where Cole's "Reidness" gets the better of him and he acts more like the man he's pretending to be than the man he is.

Then Stanley Tucci, in a minor role as the boss of the undercover team, seems not quite sure why he's in this film. It also uses Pam Grier too routinely, putting her in a role like the ones she used to get before "Jackie Brown," but not after.

Still, the real drama of "In Too Deep" is internalized: It's the struggle between the two halves of Cole's character. Omar Epps, almost asleep in the recent, awful "Mod Squad," manages exactly to get this man's torments, the seductions that he faces. It faces this stuff quite squarely, and with a great deal of raw power. There's something going on in this movie that lingers when the plot gambits have been forgotten.

In Too Deep (105 minutes, at area theaters) is rated R for graphic violence, some of it directed at women.

CAPTION: Hard hitting: Omar Epps, left, as an undercover officer, and LL Cool J as the leading thug in "In Too Deep."

CAPTION: Playing God: LL Cool J as a hard-to-resist bad guy.