With just 25 days before the first caucus votes are cast in Iowa, the leading presidential candidates in an increasingly tight race for the Republican nomination are scrambling to defend or disown their past remarks and behavior.

A torrent of embarrassing stories in the last two weeks is likely to break into a flood as campaigns let loose with the most damaging material they have on their opponents in the final three weeks of the most open presidential contest in recent history.

Mayor Giuliani, still the national Republican front-runner, offered smiles and defiance yesterday in the wake of awkward questions about his wife, his security firm, and his personal judgment.

He insisted he had little to do with arranging a taxpayer-funded security detail to protect his mistress, Judith Nathan, now his third wife, though he was not asked why the costs were hidden in accounts of obscure city agencies. The failure to address the issue will allow reporters to continue pressing for full disclosure.

“This was all based on threat assessments by the New York City Police Department, all based on their analysis to protect her life, my life, other people’s lives. They made the choice. My wife Judith would honestly prefer not to have security,” he told the host of NBC’s “Meet the Press,” Tim Russert.

When it came to business matters, Mr. Giuliani also left himself open to further probing by declining to list the clients of his security company, Giuliani Partners, one of which, the government of Qatar, is believed to have protected the ringleader of the September 11 attacks on America, Khalid Sheikh Muhammad. Giuliani Partners also has been linked in press reports to the leaders of Venezuela and North Korea, Hugo Chavez and Kim Jong Il.

The former mayor argued that naming clients would breach confidentiality, though he said that some he has advised may be “questionable.” “When you deal with clients and you take on the problems of clients and you try to help them, it may be that somewhere, someplace they did something that was questionable or arguably questionable,” he said.

“Every client of GP of any significance while I was there, while I was involved in the day-to-day operations, has been discussed” in the press, he said. “The reality is, none of them amount to anything other than ethical, lawful, decent work.”

Nor would the mayor agree to divest himself of shares in the firm. According to a statement he made in May, Mr. Giuliani earned $4.1 million from Giuliani Partners and $1.2 million from his law firm between January 2006 and February 2007.

Michael Huckabee, who has surged to just three points behind Mr. Giuliani in the latest Rasmussen national poll, denied on “Fox News Sunday” that he had ever suggested that AIDS patients should be put into quarantine, though he said he had a number of friends who had died of AIDS, one of whom was gay, and he did not deny that he considered homosexuality a “sinful lifestyle.”

While refusing to become drawn into the controversy surrounding Mitt Romney’s Mormonism, Mr. Huckabee, whom the latest Newsweek poll puts 22 points ahead of Mr. Romney in Iowa, made a sideswipe at his rival’s inconsistency. “I think people should judge Mitt Romney on his record. Is he consistent? Does he say and believe the things now that he said and believed before? That’s what ought to be the criteria. I don’t think his Mormonism ought to be a factor in it,” the former Arkansas governor, an ordained Baptist minister, said.

Mr. Huckabee was more reluctant to answer criticism that he had failed to grasp the importance of the National Intelligence Estimate on Iran a full day after it was published. Instead he turned the question on the intelligence community and criticized President Bush’s handling of national security and foreign policy.

He said he though his failure to respond to the NIE “shows more than anything is not what I didn’t know, it shows what our own intelligence community didn’t know. One of the things that I would do as president is clearly try to make sure we get some better intelligence gathering,” he said.

“We do have to make sure that we live in such a way as Americans that we have friends, not enemies, across the world. And over the past several years, it seems as we’ve made even our friends our enemies,” he said.

The theme was taken up by Senator McCain, who bemoaned the destruction by the CIA of tapes recording the interrogation of senior Al Qaeda figures.

“This destruction of tapes is now going to contribute to the cynicism and skepticism that people have all over the world. … This can’t help us in the ideological struggle we’re in against radical Islamic extremism,” he said.