DreamWorks wouldn't screen the new Chris Rock comedy for critics until the last minute. Such cowardly policy always leaves the impression that the film is a disaster . Not so. Head of State is merely a missed opportunity. There are still flashes of Rock's take-no-prisoners wit in this story of Mays Gilliam, a do-gooder alderman from Washington, D.C., who gets suckered into running for President. The party boss, Sen. Bill Arnot (James Rebhorn), means to exploit Mays. But once Mays brings on his brother Mitch (Bernie Mac, a welcome presence on any screen) to run with him as VP, the gloves are off. Like Warren Beatty in "Bulworth," Mays — ith nothing to lose — decides to tell the truth.p>ock, who wrote the script with Ali LeRoi, gets in a few good licks. "What kind of drug policy," he asks, "makes crack cheaper than asthma medicine?" And the candidate running against Mays (Nick Searcy — a cousin of Sharon Stone, no less — runs on the platform: "God Bless America-and no place else." p>This is the Rock that makes the movie rock, at least for a few scenes. But Rock as a director blunders almost as badly as Joel Schumacher did trying to blend the brashness of of Rock with the gravity of Anthony Hopkins in the misbegotten Bad Company. There are times when "Head of State" doesn't seem directed at all; you half expect the actors to crash into each other. Still, give me the attempted satire of Head of State over the racial stereotyping of Bringing Down the House anyday. You can feel a mind at work when you watch Rock. The popcorn salesmen behind Bringing Down the House stopped thinking past the box office a long time ago.