Republican vice presidential nominee Sarah Palin defied her critics with an aggressive, folksy showing in her debate clash with Democrat Joe Biden, escaping without a disastrous gaffe.

But Palin, who branded Barack Obama "dangerous" in a string of attacks on the Democratic nominee, appeared to do little to transform a race which polls suggest may be slipping away from her running mate John McCain.

The Alaska governor disappointed those who predicted she would fail miserably in the keenly-awaited primetime debate, following a tirade of mocking assessments about her credentials ahead of the election on 4 November.

"I may not answer the question the way you want to hear, but I'll talk straight to the American people and let them know my track record also," said Palin, who was wildly popular but has seen her opinion ratings fade in recent days.

Millions of Americans tuned in to watch what was touted as one of the most anticipated vice presidential debates in US history.

Often winking at the camera, Palin fired off staccato soundbites and prepped answers which often ignored the questions, in a populist tone which framed her and McCain, and not Obama and Biden, as agents of change.

"I like being able to answer these tough questions without the filter, even, of the mainstream media kind of telling viewers what they've just heard," Palin, a 44-year-old mother of five, said.

Palin has faced a storm of criticism for only doing a handful of media interviews and refusing to conduct a full-scale press conference.

Biden, a political veteran with 35 years of experience, provided detailed policy answers, trying to show a range of expertise across the economy, foreign policy and national security.

At one stage, he choked up when he talked about his wife and infant daughter killed in a 1972 car crash, in a moment which may have helped Biden forge an emotional connection with undecided voters.

Biden was careful not to attack Palin or her credentials directly, anxious about being branded as sexist or a bully, and sought to label McCain as a clone of unpopular President George W. Bush.

"I haven't heard how his policy will be different on Iran than George W. Bush's.

"I haven't heard how his policy will be different on Israel than George Bush's.

"I haven't heard how his policy on Afghanistan will be different than George Bush's, I haven't heard how his policy in Pakistan will be different than George Bush's." But Palin rebuked Biden for dwelling on the past.

"There is a time, too, when Americans say enough is enough with your ticket on constantly looking backwards and pointing fingers and doing the blame game," she said.

Snap opinion polls suggested Biden won. CNN's sampling said he took the clash by 51 to 36 percent and a CBS survey of uncommitted voters put Biden at 46 percent against 21 percent who said Palin won.

Framing herself as a typical middle-class person that goes to kids soccer games, showcasing her "hockey mom" persona, Palin painted herself as a reformer as a small town mayor and governor and an expert on energy.

"Nice to meet you, can I call you Joe?" Palin said, in a comment picked up by microphones as she first met her adversary.

"Darn right it was the predatory lenders," she said when asked whether mortgage sharks caused the subprime crisis.

The rivals clashed on the financial meltdown.

Palin warned Democrats would embrace wealth distribution and high tax policies that she said would limit growth. Biden argued that eight years of Republican policies were to blame for the economy's nightmare.

"It was two Mondays ago that John McCain said at nine in the morning that fundamentals of the economy were strong," Biden said.

"Later that day John McCain said we had an economic crisis -- that doesn't make John McCain a bad guy but it does point out he's out of touch," he said.

Palin chose not to parry a Biden claim that McCain argued against greater regulation on Wall Street, and contributed to the debt crisis.

While Palin was strongest on domestic policy, the gap in experience and knowledge was exposed when the debate turned to national security, and the Bush administration's foreign policy legacy.

She called the commander of the NATO-led security assistance force in Afghanistan "McClellan" instead of his name General David McKiernan, and her answers were often vague.

Vice presidential debates are seen as having little impact on presidential elections, although a major gaffe by Palin could have further eroded confidence in her readiness to lead and McCain's judgment in choosing her as his running mate.

Recent polls indicate that Obama leads by nearly every key measure a month before the presidential election, leaving McCain on the hunt for a sudden change of fortune to save his ailing campaign.

AFP