How desperate does a major political party have to be to back a black man for President of the United States? In the loose and canny comedy Head of State, the first joke is that the only reason the big bosses (of a fictional faction) pick small-potato D.C. alderman Mays Gilliam (Chris Rock) as their last-minute standard-bearer is so that the backroom power brokers can bank easy minority loyalty for a future election while losing this one. The opposition is so far ahead in the race with Brian Lewis (''Cast Away'''s Nick Searcy) -- a candidate who's not only a war hero but also Sharon Stone's cousin -- that even if the unnamed party's original nominee hadn't died in a freak accident, his chances would have been killed on Election Day. (Lewis' pointed campaign slogan is ''God Bless America -- and no place else!'')
The second joke is that once Gilliam shakes off his handlers, he gets both the party and the Party hopping. Barnstorming from state to state accompanied by a bow-tied campaign manager (Dylan Baker), a buttoned-down consultant (Lynn Whitfield), and an on-staff call girl (Stephanie March), Gilliam is forced to dress uptight and speak TelePrompTer-ready bull on a theme of ''People like you are the backbone of America!'' But after his older brother Mitch (Bernie Mac) slaps him upside the head -- literally -- and urges him to get real, Mays goes off script and preaches truth to power. ''Takin' your pensions -- that ain't right!'' he exhorts a fired-up crowd. ''That s--- is wrong.'' Pretty soon, the most soulful candidate since Bill Clinton has gotten stuffy white folks on their feet to dance the electric slide at a fundraiser. It's a tribute to the threat he poses that his opponent begins to run negative ads: ''Mays Gilliam: He's for cancer!''
Anyhow, Rock's s--- is right. As a first-time director working from a well-made script he cowrote with longtime creative partner Ali LeRoi, the comedian has hit on a fleet, slightly unfinished-looking, and invitingly improv-ish personal cinematic style. And it's one that's a much better fit for his disarmingly smart observations than ''Down to Earth'' ever was. There's a lot of exuberant, nutty, try-it-and-move-on stuff spread around: A harpy of an ex-girlfriend (Robin Givens) who wants to sink her claws back into Gilliam now that his career is on the rise is regularly yanked off camera with a slapsticky tug appropriate for ''Amateur Night at the Apollo''; ''SNL'''s Tracy Morgan appears, for no good reason, as a local regularly trying to fence cellophane-wrapped stolen meat; the funky hip-hop master Nate Dogg regularly appears as himself, for very good reason, crooning his Greek-chorus commentary on the action like Jonathan Richman did in ''There's Something About Mary.'' And I love the notion of ''Law & Order: SVU'''s March as an efficient in-house superwhore. (Gilliam doesn't make use of her services -- he's sweet on a good-hearted cashier played by Tamala Jones.)
The rhythms are all over the place in ''Head of State,'' and not all of them are steady; Rock is most prone to stumbling when he tries to shoehorn stand-alone, stand-up lines into the action. (''You can get shot while you're getting shot,'' Mays says of the run-down D.C. neighborhood he represents.) More valuably, though, Rock, one of the most astute comic talents working today, revels in impassioned commentary about the state of American politics and race relations, all imparted with a grin, a twinkle, and a reliable crap detector: His movie is as blithe and fearless in talking about race as ''Bringing Down the House'' is nervous and coy. Decked out (once he sheds his safe, conservative suits) in a dazzling wardrobe of ghetto-fabulous threads, the star bounces through his own movie with authority, goodwill, and -- for all his gibes -- serious purpose.
Indeed it's just that confidence that allows Rock to bring on the magnificent Bernie Mac (himself a commanding vision in rainbow-colored ensembles) and, with the pride of a successful younger brother, let Mac's own powerful comedic personality out to play. In scenes together, the two exult in the kind of highly charged verbal and physical antics that are star-turn rewards for performers currently at the tops of their games. And when Mac is on the campaign trail himself as Gilliam's vice presidential running mate, his Mitch pretty well flattens every one of his interviewers, either with his motor mouth or with his big-guy meat hooks.
''I represent my whole race,'' Gilliam comes to realize, as the importance of what he's doing sinks in some 30 years after Robert Redford represented the daring Hollywood notion of a liberal idealist set up to lose a senatorial election in ''The Candidate.'' ''Head of State,'' in turn, does right by Rock, both as a performer and as a director. Here, he's an artist who dares to envision an America ready to vote for a black man, at least on screen. It's a start.