US presidential hopefuls returned to the campaign trail on Wednesday after a pause for Christmas with the latest opinion poll showing Hillary Clinton regaining the lead among Democrats in Iowa a week before the state's first-in-the-nation caucuses.

Earlier polls had the New York senator locked in a dead heat with Barack Obama in Iowa, with John Edwards close behind.

The survey offered reassurance to Mrs Clinton after a tough few weeks during which her campaign appeared to lose momentum while Mr Obama surged back into contention.

After months spent trumpeting her strength and experience, Mrs Clinton has spent recent days campaigning alongside her mother and daughter across Iowa in a belated attempt to soften her harsh public image.

But the main narrative to the Democratic race remains the perceived choice between Mrs Clinton's greater experience and Mr Obama's promise of change.

While the ARG poll showed Mrs Clinton back in command, the survey found the Republican contest tightening into a dead heat between Mitt Romney, the former governor of Massachusetts, and Mike Huckabee, the former governor of Arkansas.

Mr Huckabee had opened a double-digit lead in Iowa over recent weeks, bolstered by support from Christian conservatives. But Mr Romney, who had led in the state for most of this year, appears to be clawing back lost ground.

Iowa's caucuses on January 3 mark the first of the state-by-state contests that will determine each party's nominee in next November's presidential election.

Candidates hope a strong performance in Iowa and New Hampshire, which holds its primary election on January 8, will propel them towards their party's nomination.

In New Hampshire, polls show Mrs Clinton with a narrow poll lead over Mr Obama in the Democratic race, while Mr Romney heads the Republican field with John McCain, senator for Arizona, gaining ground in second place.

Rudy Giuliani, the former mayor of New York, is trailing in fifth place in Iowa and third in New Hampshire but hopes victories in several states that vote later in January and early February will catapult him back into contention for the Republican nomination.

By Andrew Ward, Financial Times, December 27, 2007