BETHLEHEM, N.H. - Mitt Romney, seemingly happy with how the Republican presidential campaign is playing out, is not explaining or apologizing for TV attack ads paid for by his allies that have damaged his chief rival's standing days before the Iowa caucuses.

Whether he's the true front-runner or not, Romney is acting like one. He has refused to be dragged into debates about the campaign's tone or high-stakes brinkmanship in Congress - or into a one-on-one debate sought by Newt Gingrich.

Gingrich, the former House speaker, has repeatedly called on Romney to face him before cameras and defend the ads, which are largely financed by a heavily bankrolled group friendly to Romney.

The former Massachusetts governor said: "We've had many occasions to debate together, and we'll have more, I presume quite a few more, before this is finished. But I'm not going to narrow this down to a two-person race while there are still a number of other candidates that are viable."

Some party insiders expect a strong showing in the leadoff Iowa caucuses Jan. 3 by libertarian-leaning Rep. Ron Paul of Texas. But they generally see Gingrich as having the best chance to compete with Romney for weeks or months.

Gingrich and Romney planned to campaign through Friday, underscoring the stakes for both candidates even as the pace by the crowded field began to lighten for Christmas weekend. The barrage of ads, though, kept up in Iowa and New Hampshire.

In a sign of his late organizing start, Gingrich spent Thursday in Virginia, scrambling to secure the 10,000 voter signatures he needs to get on the state's March 6 primary ballot. It cost him a precious day of campaigning in Iowa and in New Hampshire, which holds its primary Jan. 10.

Texas Gov. Rick Perry has been by far the heaviest spender in Iowa. But his campaign this week gave 30-day termination notices to all political consultants in Iowa, New Hampshire, and South Carolina. Aides said the campaign was moving toward fiscal discipline as it prepares for a long multistate strategy.

But even in states that vote early, political consultants rarely receive such notices. Some are usually retained with an eye toward the general election, or sent to other states.

Gingrich renewed his call for Romney to condemn or defend ads sponsored in Iowa by a so-called super PAC. It's run by Romney supporters who are legally barred from coordinating with the official campaign.

Romney, interviewed during a bus tour of New Hampshire, didn't take the bait.

"I'm not in any way coordinating the ads or the approach that's taken by the super PAC," he said.

Gingrich scoffed, saying Romney could easily condemn the ads without breaking campaign-finance laws.

"It tells you a lot about Gov. Romney," Gingrich said in Richmond, Va. "I'm happy to go all over Iowa and point out that he doesn't mind hiding out behind millions of dollars of negative ads, but he doesn't want to defend them. The ads are false."

Ads showing in Iowa accuse Gingrich of supporting amnesty for illegal immigrants, and remind voters of his 1998 ethics problems in Congress, which involved his paying a $300,000 penalty. More subtle ads tout Romney's 42-year marriage, an indirect swipe at Gingrich's two messy divorces.

Gingrich said some ads dealing with abortion are inaccurate. Iowans will not reward "falsehoods by millionaires," he said.

Some prominent Republicans came to Romney's defense. Former New Hampshire Gov. John H. Sununu, a Romney supporter, said he was getting tired of Gingrich's "whining."

And former President George H.W. Bush told the Houston Chronicle that Romney is the best choice for president. "I like Perry, but he doesn't seem to be going anywhere," Bush said.