White House race begins

Des Moines, Iowa: Voters in Iowa began the process of choosing the next US president on Thursday, and a new poll showed Barack Obama leading John Edwards in the Democratic nominating contest - with Hillary Clinton falling to a potentially disastrous third.

The Reuters/C-SPAN/Zogby poll also showed Republican Mike Huckabee expanding his lead on rival Mitt Romney as the most heavily contested presidential caucus in Iowa history drew to a close.

For the winner in Iowa, the prize is a valuable shot of momentum and at least a temporary claim to the front-runner's slot in their party's nomination battle.

The third-place finisher in the heavyweight Democratic showdown, meanwhile, could find themselves severely wounded heading into the next contest in New Hampshire on Tuesday.

For Clinton, who a few months ago was declared in some quarters the almost certain Democratic nominee, a third-place finish in Iowa would be a heavy blow and would create immense pressure for a win in New Hampshire next Tuesday.

Huckabee, the former Arkansas governor whose bare-bones campaign has steadily climbed since a second-place finish at the Iowa straw poll in August, expanded his lead over Romney in the Republican race to 31 per cent to 25 per cent. He took a brief break from frigid Iowa to fly to California and appear on The Tonight Show with Jay Leno, playing bass with the house band and crossing a picket line to appear on the show while expressing support for striking writers.

A Huckabee spokesman said he only agreed to the appearance after being assured no replacement writers were being used.

Iowa opens the state-by-state battle to choose candidates in the November election to succeed President George W. Bush, and traditionally has served to winnow the field of laggards and elevate some surprise contenders.

The 2008 campaign is the most wide open presidential race in more than 50 years, with no sitting president or vice-president seeking their party's nomination. The Democratic caucus begins at 6:30pm CST (0030 GMT), with Republicans starting 30 minutes later. Results could begin to appear within an hour or two.

Record turnout is expected for the Democrats, surpassing the 124,000 Iowans who participated in 2004. Republicans are also likely to surpass their record of 87,000 caucus participants in 2000.