MISSOURI - US VOTERS braced for the most anticipated vice presidential debate in history on Thursday amid speculation that Republican Sarah Palin could stumble before millions of viewers.

Concern about Mrs Palin's readiness has mounted in recent days following a series of cringe-inducing interviews in which Mrs Palin, a first-time Alaska governor, has been sometimes lost for words when faced with tough questioning.

How the Palin-Biden debate could play out WASHINGTON - THE showdown on Thursday between Republican Sarah Palin and Democrat Joe Biden is the only vice-presidential debate of the White House race, and it has attracted more attention than usual because of high interest in Mrs Palin. Mrs Palin, the governor of Alaska, was a virtual unknown when John McCain tapped her to be his No. 2 in August. But the mother of five quickly became a celebrity and rallied enthusiasm among conservatives. ... more Joe Biden, Democratic vice presidential candidate DEMOCRATIVE vice presidential candidate Joe Biden debates his Republican rival Sarah Palin on Thursday in their sole face-to-face confrontation before the Nov 4 election. The following are some biographical details for Mr Biden, a US Senator from the state of Delaware: ... more Sarah Palin, Republican vice presidential candidate REPUBLICAN vice presidential candidate Sarah Palin debates her Democratic rival, Joe Biden, on Thursday in their only face-off before the Nov 4 presidential election. The following are some biographical details for Mr Palin, a little-known Alaska governor before she was chosen as Mr John McCain's running mate: ... more

Accusations have flown that Mrs Palin was overhandled and underexposed on the campaign trail and expectations are low as she prepares to square off against her Democrat rival Joe Biden in their sole clash ahead of the November 4 election.

The governor burst onto the national scene when John McCain picked her as his running mate, energising the conservative Republican base with her positions on abortion, gun rights and her background as a moose hunting, deeply Christian mother of five from the northern frontier.

But the bloom is fading and some Republicans are fearing a fiasco.

On Wednesday, Mrs Palin spent the final full day of intensive training at Mr McCain's Arizona ranch.

In recent days she has faced widespread ridicule for the few interviews she has granted, including for citing Alaska's proximity to Canada and Russia as giving her foreign policy experience.

At least two renowned conservative columnists - keen to back Mrs Palin when she was announced as Mr McCain's running mate - are in open revolt and calling her unqualified for the job.

Writing in the conservative National Review, columnist Kathleen Parker said Mrs Palin should step down, while Dallas Morning News editorial columnist Rod Dreher wrote that he is no longer backing McCain-Palin.

Some political analysts and experts said MrsPalin as facing her most crucial test just 34 days before mericans head to voting booths.

'It's make-or-break for her in the sense that, in a three-game series, her record so far is one and one: the convention and the interviews,' Washington University history professor Peter Kastor said.

Her speech brought the house down at the Republican convention at the beginning of September.

'This (debate) could be what seals the deal. If she does extremely well or extremely poorly, obviously it will be the debate that people say defines Sarah Palin's candidacy,' Prof Kastor said.

Presidency scholar at St. Louis University, Joel Goldstein said the Biden-Palin debate has a 'unique level of fascination', primarily because there has been 'so little exposure so far of Governor Palin'.

Mr Goldstein and other experts described it as the most anticipated vice-presidential debate since they debuted back in 1976.

In the build-up to Thursday's showdown, Palin acquaintances from Alaska framed the candidate as an effective debater.

Anchorage Daily News editor Larry Persily described how Mrs Palin 'flummoxed her rivals like Muhammad Ali around the ring.'

Mr Tony Knowles, former governor of Alaska, said Mrs Palin 'is an attractive candidate with a unique ability to emotionally connect with the audience.'

This week Mr McCain has sought to help Mrs Palin navigate a media minefield.

In response to the attacks, Mr McCain struggled on Wednesday to convincingly answer a National Public Radio reporter's question on whether he would ask for foreign policy advice from his running mate.

'I've turned to her for advice many times in the past,' Mr McCain told a journalist from NPR, without specifying on what subjects.

Ahead of the debate, Mrs Palin, 44, told a rally in Ohio that she had never met Mr Biden. 'But I've been hearing about his Senate speeches since I was in, like, second grade,' she quipped.

When asked by CBS interviewer Katie Couric if that was a risky thing to say considering Mr Palin's own running mate is 72, the governor replied: 'Oh no, it's nothing negative at all.'

'He's got a tremendous amount of experience and, you know, I'm the new energy, the new face.'

Mr Biden, a 35-year veteran of the Senate, is known for being gaffe-prone, and he runs the risk of sounding condescending or patronising when he faces off against Mrs Palin.

Last month he told a campaign rally that he will not let things get personal at the debate.

'The way I was raised is: I never, ever, ever attack the other person,' Mr Biden said. 'I will take issue with her as strongly as I can.' -- AFP