Hillary Clinton and Mitt Romney were scrambling to rescue faltering presidential campaigns yesterday as opinion polls showed momentum continuing to shift against them ahead of tomorrow's New Hampshire primary.

Mrs Clinton, the longtime Democratic frontrunner, and Mr Romney, one of the leading Republican contenders, have both seen poll leads evaporate in New Hampshire since defeats in last week's Iowa caucuses.

Barack Obama, the African-American senator for Illinois, has surged and is now neck and neck with Mrs Clinton, the senator for New York and former first lady, on the back of his Iowa victory.

In the Republican race, Mr Romney, the wealthy former governor of Massachusetts, has fallen behind John McCain, the veteran Arizona senator who has staged a surprise comeback.

A second successive defeat for either Mrs Clinton or Mr Romney would leave their presidential hopes hanging by a thread heading into the barrage of other state primaries and caucuses in the next few weeks.

Mr Obama is hoping a surge of support from independent voters, who are expected to make up about 40 per cent of New Hampshire's primary electorate, will help carry him to victory. Independents and young voters swung heavily behind him in Iowa last week, drawn by his promise to bring change and unity to Washington after years of partisan gridlock.

"We are seeing clear movement in Obama's direction," said pollster John Zogby. The Republican race was too close to call. But Mrs Clinton sought to fight back over the weekend by arguing she was better equipped to deliver the change voters wanted. "There's a big difference between talking and acting, between promising and performing," she said yesterday.

In a televised debate on Saturday, Mrs Clinton raised her voice and jabbed her finger as she declared: "I'm not just running on a promise of change. I'm running on 35 years of change."

Using similar tactics to Mrs Clinton, Mr Romney yesterday argued his record as governor and in the private sector proved his ability to deliver change.

During Saturday's Republican debate, Mr Romney faced almost remorseless criticism for his inconsistent record on abortion and other contentious issues.

Mike Huckabee, Republican winner in Iowa, is trailing in third place in New Hampshire.