Democratic presidential candidate Hillary Clinton battled to keep crucial New Hampshire from swinging to rising rival Barack Obama on Sunday but new polls showed him jumping into the lead.
In the hotly contested Republican race, Arizona Sen John McCain leaped ahead of former Massachusetts Gov Mitt Romney even as Romney tried to raise doubts about McCain.
New Hampshire's primary is the next battleground in the state-by-state process of choosing Republican and Democratic candidates for November's election to replace President George W Bush.
Republican candidates bickered over the Iraq war, illegal immigration and taxes in a Fox News Channel debate on Sunday night.
Romney and former Arkansas Gov. Mike Huckabee, who won Iowa last week, accused each other of raising taxes in their states. "Mike, you make up facts faster than you talk," Romney told Huckabee.
And McCain accused Romney of not raising questions about Bush's war strategy when Defense Secretary Donald Rumsfeld was running it from 2003-06. Romney replied he had a state to run at the time.
Obama, an Illinois senator seeking to be the first black U.S. president, built on his victory in Iowa last week with a significant bounce in New Hampshire, which votes on Tuesday.
A USA Today/Gallup poll said Obama had opened up a 13-point lead over Clinton in New Hampshire, 41 per cent to 28 per cent, to 19 per cent for former North Carolina Sen John Edwards.
A WMUR/CNN poll showed Obama leading Clinton, 39 per cent to 29 per cent. Earlier polls had shown the race to be a dead heat between Clinton and Obama.
Clinton on the attack
A loss in New Hampshire would be a significant blow to Clinton in the New York senator's drive to become the first woman US president.
Trying to salvage New Hampshire, the former first lady engaged in some of her heaviest attacks against Obama in the months-long campaign.
In Nashua, Clinton said that while Obama talks a lot about changing the United States, she believes she has actually carried out change. Change from the Bush administration is a leading theme in the presidential campaign. "It is about how we bring about change by making sure we nominate and elect a doer and not a talker, that we begin to separate out rhetoric from reality," Clinton told a large, enthusiastic crowd in Nashua.
Accusing Obama and Edwards of not showing leadership on a litany of issues, she said, "That's not change," and the crowd joined in with her. "That's not change," they yelled.
Obama, at a rally at a high school in Salem, fired back: "We don't need our leaders telling us what we can't do. We need our leaders to believe in what we can accomplish."
The Clinton campaign also complained of the Obama camp making automated prerecorded calls to New Hampshire residents who had registered on an official "do not call" list, a practice that would violate state law. The Obama campaign dismissed the complaint and said no law was broken.
The race was taking a negative turn on both sides in a state that is vital to efforts by Clinton and Romney to revitalize their campaigns after disappointing showings last Thursday in Iowa.
Obama received the endorsement of former New Jersey Sen. Bill Bradley, who finished a close second to then Vice President Al Gore in the 2000 Democratic primary here.
McCain ahead of Romney
The USA Today/Gallup poll said McCain had taken the lead over Romney, 34 percent to 30 percent, with Huckabee in third at 13 percent.
A win for McCain in New Hampshire would be a remarkable turnaround for him after his campaign suffered money problems last summer and was all but given up for dead.
Romney, who would be the first Mormon president, needs to win or finish high in New Hampshire to maintain his credibility.
At a rally in Nashua, Romney said he doubted McCain would stand up well against Obama, who he said was succeeding against veteran Democratic senators in the presidential race. "Are we going to do the same thing and put another long-serving U.S. senator up against him for him to talk about. Or are we going to put somebody -- I hope it's me -- somebody who has spent his lifetime not just in politics, not in Washington, but changing things?" Romney said.
(Additional reporting by John Whitesides, Mark Egan in New Hampshire, Missy Ryan, Leslie Wroughton and David Wiessler in Washington)