A woman a sassy, roly-poly hot mama wanders into the police station bearing a bouquet for Detective Murtaugh (Danny Glover), whom she's fallen for madly. Murtaugh himself is nowhere to be found he has ducked behind the nearest desk and so she relays her romantic message through his partner, the redoubtable flake Riggs (Mel Gibson). ''You tell that man,'' she says, ''that he's the jaaam in mah jelly roll!''
You want comic relief? In Lethal Weapon 3, you get comic relief. In fact, you get it long after the crime-thriller razzmatazz should be shifting into overdrive.
The first Lethal Weapon was a state-of-the-art piece of high-octane pulp. It was the same action-thriller demolition derby we'd been watching for years, only revved up, made wilder and funnier, more jauntily disposable. Lethal Weapon 2 delivered even greater kicks, with Gibson and Glover tossing jibes at each other as if they were playing badminton with firecrackers. So what's left for Lethal Weapon 3? Scraps, I'm afraid. The movie is like a pile of odds and ends some suitably entertaining that never made it into the first two films. Instead of shooting the works, director Richard Donner skimps on the basics: villain, plot, logic, suspense. ''If you want those,'' Donner seems to be saying, ''go rent The French Connection.''
Lethal Weapon 3 has something to do with Riggs and Murtaugh trying to nail an ex-cop (Stuart Wilson) who has been selling illegal firearms to street gangs. At least, I think that's what he's doing this baddie has such a perfunctory role we barely see him committing crimes. There's an attempt to give the weapons business a topical spin: For a few minutes, the movie turns into a just-add-tears version of Boyz N the Hood. But it's the silliest hypocrisy to inject ''antiviolence'' sentiment into a cartoon-nihilist bash like Lethal Weapon 3. The series was more honest, and more fun, when Riggs was jumping off roofs.
There are other letdowns. Joe Pesci, as the bleached-blond hustler Leo, shows up just infrequently enough to remind you he's there for no other reason than to reprise his role. More impressive is Rene Russo, playing an Internal Affairs officer with a kick-ass karate chop. With her beautiful big jaw, she's like a '40s siren reborn as a '90s terminatrix.
The movie zips around without any true forward momentum. The stars carry you along, though. As Murtaugh, Glover walks a witty line between slyness and exasperation. And Gibson drops his zingers with such supercharged flipness that he seems to be carrying on his own private, Mad-magazine commentary on the action; he's like a talking doodle in the margin. Gibson has become an ace comedian, but he'd do well to remember that there's a thin line between self-satire and self-indulgence. Time to invent some new weapons. C+