This Bruce Willis-Mos Def buddy-movie action comedy-drama is basically an outdoor version of “Assault on Precinct 13,” but though it’s a formula piece all the way, the chemistry between the leads and knowing direction from Richard Donner help it overcome the script’s manifest implausibilities and provide a reasonably good time. “16 Blocks” is just a popcorn movie, but unlike many examples of the genre, it’s an expertly crafted, enjoyable accompaniment to the kernels.

Willis, sporting a heavy five-o’clock shadow and prominent paunch to go along with his tired tread and exhausted manner, plays Jack Mosley, a burned-out, alcoholic detective on the NYPD. He’s assigned an onerous task one morning, just as he’s leaving the squad room–escorting a small-time hood named Eddie Bunker (Def) from a holding cell to an appointment with the grand jury downtown, where he’s scheduled to testify. Bunker, a loquacious, inquisitive fellow, immediately irritates Mosley; but when the cop stops to buy a bottle of booze and a couple of guys try to off his prisoner, the detective saves the fellow and calls for backup. Unfortunately, the colleagues who arrive–led by Jack’s old partner Frank Nugent (David Morse)–turn out to be behind the attempt to wipe out Eddie, who’s going to provide information on dirty cops, and their intervention forces Mosley either to allow them to kill Bunker and make it look like a justified shooting or to protect him against them and get him to the courthouse.

What follows is an elaborate chase, with Mosley and Bunker going through a series of clever evasions and close-shave escapes, bonding in the process. (The process is accelerated, despite Jack’s initial reluctance, by his realization that Bunker may be a low-life, but he’s really trying to turn himself around, and by a revelation about Eddie’s background.) Some of these episodes are rather clumsily comic (like one involving an elderly Chinese man) and others are almost absurdly over-the-top (particularly a lengthy sequence featuring a highjacked bus and some hostages), but they’re sufficiently well staged by Donner that while you can’t quite swallow them, you’re willing to let that pass and just sit back and take pleasure from the nice execution.

The ability to suspend disbelief just enough to have a good time is aided by the leads. Willis may be a trifle obvious in his weatherbeaten effects, and a twist Richard Wenk’s script gives to his character in the later going doesn’t quite work, but he mostly carries it off. And Def does what he needs to, which is to make Bunker a likable rogue. At first the voice he affects–nasal and strangulated–comes off as not just affected but really annoying, and the fact that he’s able to make the vocal delivery not only palatable but almost charming over the long haul is remarkable. Morse does his usual yeoman service as the nasty (and, as it turns out, pretty inept) Nugent, and Donner gets serviceable work from the rest of his large supporting cast.

On the physical side, “16 Blocks” is a solid piece of work, with fine cinematography by Glen Macpherson, who uses shadows, widescreen composition and bleached-out colors to fine effect (and also gets Toronto to stand in reasonably well for NYC). Klaus Badelt’s score is supportive without intruding overmuch, too. One curious fact about the movie is that if you count up the number of producers–full, co-, executive and co-executive–you get the same number as in the title. But if “16 Producers” is likely to be pure serendipity, the quality of “16 Blocks” would appear the result of solid craftsmanship on both sides of the camera. It may not be the best cinematic jaunt you’ve ever encountered, but at least it’s not one of those action movies that misses by a country mile.