George W. Bush's campaign, in its harshest language to date against a GOP presidential rival, is accusing Steve Forbes in an Iowa radio ad of "slinging mud and distorting records."

While the spot doesn't mention Forbes, Bush campaign spokesman Ari Fleischer confirmed it is aimed at the wealthy publisher.

In the ad, Sen. Charles E. Grassley (R-Iowa) says of the allegedly mud-slinging candidates: "You might receive their misleading phone calls, negative mail, or see and hear their attack ads. . . . Hang up the phone, throw the mail out and change the station."

What's Grassley talking about? While Forbes has run ads assailing Bush's record, Fleischer said the line about phone calls and mail is a reference to Forbes's conduct in the 1996 campaign. "Governor Bush's position is, you can judge people's actions by what they've done in the past," he said. Asked if the ad implied that Forbes is using negative calls and mail, Fleischer said it used the word "might."

Forbes spokesman Greg Mueller denied that his candidate employed such tactics in 1996. Press reports then said that Forbes was a target of so-called push polling, involving the use of loaded questions, by Robert J. Dole's campaign.

"Every four years, the establishment--in this case the Bush campaign--tries to muzzle the conservative challenger in the race," Mueller said. "We're not going to be intimidated. Their idea of a negative campaign is challenging someone on the issues."