John McCain's camp has hit back after Barack Obama's campaign charged his White House bid was based on "disgusting lies", accusing Democrats of reeling in "full throated panic".

The Democratic hopeful meanwhile said he had smashed his own record and raised $US66 million ($A82.4 million) last month, grabbing a leg-up in the frenetic seven weeks of no-holds-barred, coast-to-coast campaigning until the election.

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Republicans went on the offensive after Obama launched a fierce counter-attack last week as his poll numbers ebbed and Republicans rode a wave of enthusiasm following McCain's choice of Sarah Palin as his running mate.

"The Democratic Party is in full-throated panic over Sarah Palin," said McCain ally and former top business executive Carly Fiorina, on ABC News program This Week, lambasting US columnists who accused McCain and Palin of telling lies.

Fiorina also complained "ageism" was rampant, with Obama partisans arguing that Palin, a first-term Alaska governor and 44-year-old mother of five, was too inexperienced to serve as vice-president.

The Obama camp raised the age issue implicitly last week when it ran an ad mocking the 72-year-old McCain as out of touch and oblivious to the internet revolution.

"I frankly find this disrespectful in the extreme. This is ageism," Fiorina said.

"All you need to do is look at the schedule that John McCain has kept for the last two years to realise that he is one of the most vigorous, most energetic campaigners, frankly, in my judgment, out there.

"This continued resort to 'he's too old' is desperation, frankly."

But Democratic Senator Claire McCaskill raised questions about the experience of McCain's running mate, saying on the same show: "We're talking about a reality here that we have to face.

"This is someone who's going to be one heartbeat away from the presidency."

Former New York mayor Rudolph Giuliani blamed Obama for the negative lurch of the campaign, saying it was a direct result of his refusal to accept McCain's call in regular town hall meetings.

"I agree the campaign has gotten too negative on both sides," the Republican icon said on NBC program Meet the Press.

"The main reason for that is that Senator Obama has refused to debate in these town hall meetings every week."

The Republican fightback came after Palin faced new accusations on Sunday of handing jobs to friends as Alaska governor.

The New York Times reported she granted the $US95,000-a-year ($A118,000) directorship of the state division of agriculture to a high school classmate, Franci Havemeister, who cited her childhood love of cows as a qualification.

Havemeister was one of at least five schoolmates Palin hired, often at salaries far exceeding their private sector wages, the paper said.

Democrats accused the McCain campaign of adopting a scorched earth policy against Obama, after charging he called Palin a pig and backed teaching sex education to kindergarten children.

Obama spokesman Bill Burton accused McCain of "running the sleaziest and least honourable campaign in modern presidential campaign history.

"His discredited ads with disgusting lies are running all over the country today. He runs a campaign not worthy of the office he is seeking."

Obama has announced a record-breaking August, in which he piled up $US66 million ($A82.37 million) for the crucial run to the November 4 election.

McCain raised $US47 million ($A58.6 million) in August - his best month so far. But the Republican has accepted public financing for his effort, which limits his spending to $US84 million ($A104.8 million) until the November 4 election.

Obama will seek to press home his advantage through large-scale advertising blitzes, seek to stretch McCain's limited resources across the electoral map and fire up a massive get-out-the vote effort.

Latest polls showed a tight race, with a slim advantage to McCain.

The Republican led by three points by 50 to 47 per cent in Sunday's tracking survey by Rasmussen. Gallup's latest snapshot had McCain up 47 per cent to 45 per cent.

But Obama opened up a 12-point lead in the midwestern battleground of Iowa, 52 per cent to 40 per cent, according to a Des Moines Register poll. The state went Republican in 2004.