The ad involving Forbes is in response to a spot the conservative publisher is airing in early voting states that accuse Bush of breaking a no-tax pledge during his tenure as Texas' governor. It is tentatively scheduled to air this week in Iowa, with the Bush campaign waiting to make sure Forbes' spot airs as widely as promised.

In South Carolina today, Bush faced questions about a critical ad that never aired. A college student who was volunteering for Bush in New Hampshire said she was asked by his campaign to criticize Sen. John McCain's tax plan. The woman is now volunteering for McCain.

Bush said today she should not have been asked to criticize the Arizona senator.

"The ad will not run," Bush said. "I'm going to treat my friend and opponent with respect. He deserves to be treated with respect. He's a buddy, but he's not right on the tax plan."

In a draft of the Bush ad set for Iowa, Bush promises to run a campaign free of "cynical and negative politics" and suggests, without naming him, that Forbes has not done so. "My opponent has chosen to run a negative campaign," Bush says, according to an adviser who read from the draft.

Bush hopes to capitalize on lingering resentment among some Iowa voters toward Forbes' 1996 critical ad campaign that hindered Bob Dole, the eventual GOP presidential nominee.

Bush's internal polls have indicated that Forbes would be vulnerable to accusations that he is going negative. The Bush campaign has been prepared since the beginning to level the negative charge against Forbes as soon as he turned critical of Bush.

Forbes' ad began running last week, and has not been on the air long enough to determine its effect on Bush, the adviser said. But the governor's team did not want to wait until damage had been done.

Forbes had already received priceless attention by raising the accusation during a GOP presidential debate Monday night in Michigan.

In focus groups last year, the Bush team tested the impact of ads it produced to look like Forbes attacking the governor. At least one of those mock ads involved Bush's tax record in Texas.

A separate ad will soon run in New Hampshire promoting Bush's $483 billion, five-year, tax-cut plan, with Bush assuring voters he could cut taxes and protect Social Security.

"This is opportunity to talk about what I intend to do," Bush said today in Lexington, S.C. "It's an opportunity to remind people I've got a record of cutting taxes."

McCain, who is running even with Bush in New Hampshire, has accused Bush of proposing to spend too much on tax cuts and nothing to shore up Social Security.

Also running in New Hampshire is a so-called "real time" ad that takes a veiled slap at McCain. The real-time ads consist of footage of Bush campaign events that are rushed into production and onto the air by Bush's media team. In the latest spot airing Tuesday in New Hampshire, Bush tells viewers the surplus could grow by $800 billion -- more than expected. "That makes the idea of having a paltry tax cut even more risky," Bush says.

While the ads display Bush's ability to fund an aggressive ad campaign, the separate responses to McCain and Forbes also underscore a disadvantage: Only the front-runner must deal with multiple criticisms.

It was unclear how much Bush was spending on the first two ads, but the adviser said they would be rolled into his heavy advertising schedule.