Rob Reiner regrets making a political ad -- The actor now regrets aligning himself with presidential candidate Jerry Brown

Having a hard time grasping presidential contender Jerry Brown’s flat tax notion? So, in more ways than one, is Rob Reiner, who made a commercial for Brown with his old All in the Family colleague and Brown supporter Carroll O’Connor.

In the ad, O’Connor’s archconservative Archie Bunker wheelbarrows in volumes of the federal tax code and attempts to explain Brown’s simplifying proposal to his stupified son-in-law, Reiner’s Mike ”Meathead” Stivik. Now, after the spot has aired in five states and is slated to run in California before the June 2 primary, Reiner says he feels like a lunkhead for making it. The source of his unhappiness? The ad was produced before Brown announced Jesse Jackson as his potential running mate.

Reiner, a conspicuous no-show at a recent Brown celebrity fund-raiser in Santa Monica, won’t comment, but Fred Goldey of American Videogram, which produced the ad, says, ”I realize Rob is very Jewish. I understand Jews have a problem with Jackson.” How are Brown’s people taking it? ”Hold on, this is getting too complicated,” says Ileana Wachtel, Brown’s national press secretary, who declines further comment.