Republican vice presidential pick Sarah Palin lashed out at Barack Obama and styled herself as a crusader against the elite Washington establishment in her high-stakes convention debut.

The Alaska governor, in the most important speech yet to the party bonanza that will nominate John McCain, defended her credentials to serve as vice president, saying she was steeped in executive leadership experience.

“Here is how I look at the choice Americans face in this election," the 44-year-old mother of five said in excerpts of her intensely anticipated speech.

"In politics, there are some candidates who use change to promote their careers. And then there are those, like John McCain, who use their careers to promote change,” she added.

The speech represented a key moment in a Republican bid to quell a personal and political storm raging around Palin, which led Democrats to question McCain's judgement and the extent to which he vetted his shock choice.

Palin also painted herself as an outsider, primed to go to Washington to launch a wave of reform, in line with McCain's narrative that he is a maverick reformer.

"I am not a member of the permanent political establishment and I have learned quickly, these past few days, that if you're not a member in good standing of the Washington elite, then some in the media consider a candidate unqualified for that reason alone. But here's a little news flash for all those reporters and commentators: I'm not going to Washington to seek their good opinion I am going to Washington to serve the people of this country," the Republican vice presidential pick said.

Palin also noted that she had served as a smalltown mayor in her native Alaska, saying in another swipe at Obama that the job was like being a community organizer "except that you have actual responsibilities."

Obama got his start in politics as a community organizer in Chicago after law school.

Republicans were sure to give the Alaska governor a rapturous reception, but she has a tougher job to court millions of voters watching on television after her rocky rollout as McCain's running mate.

Since she was picked on Friday, Palin has disclosed that her unwed teenage daughter was pregnant, faced claims she abused her power as governor and mayor of a small town, and sought federal cash for programs opposed by McCain.

But Palin has managed to do what McCain could not in 18 months on the stump electrify the crucial core conservative base of the Republican party, based on her staunch opposition to abortion and position on key social issues.

McCain flew into Minneapolis-St Paul airport on Wednesday, and gave Palin a warm embrace, and in full view of television cameras hugged her pregnant daughter Bristol and shook hands with the father of her child, Levi Johnston.

Republicans meanwhile rode to Palin's defense.

"Governor Palin represents a new generation," said former New York mayor Rudolph Giuliani in excerpts of his Wednesday convention speech.

Former Republican presidential candidate Mike Huckabee meanwhile lashed out at Obama's foreign policy.

"Maybe the most dangerous threat of an Obama presidency is that he would continue to give madmen the benefit of the doubt," Huckabee said in advance excerpts of his speech.

Other senior Republicans also launched a searing attack against Obama on Wednesday, branding him as an extreme liberal with a foreign policy that would cede power to "madmen."

Palin's speech comes amid signs of rising political pressure on McCain as a new poll in battleground states Iowa and Minnesota showed Obama pulling out a wide lead with only two months to go to the November 4 election.