WASHINGTON - FALLING behind in the polls one month before Election Day, Republican John McCain stepped up efforts to portray Barack Obama as too unacceptable for American voters.

His vice presidential candidate Sarah Palin accused the Democratic nominee of 'palling around with terrorists'.

The onus is on Mr McCain to turn the race around under exceptionally challenging circumstances. With the economic crisis working to Mr Obama's advantage, the Democratic nominee has surged into the lead in both national polls and surveys of key battleground states, including Republican-leaning Virginia, North Carolina and Florida.

Mrs Palin's attack on Saturday came after Mr McCain's advisers indicated the Arizona senator's campaign will ramp up his attacks in the coming days with a tougher, more focused message describing 'who Obama is,' including questioning his character, 'liberal' record and 'too risky' proposals.

Mr Obama's advisers, in turn, say he will argue in the campaign's closing weeks that Mr McCain is unable to articulate an economic vision that is different from President George W. Bush's unpopular policies.

Senator Hillary Rodham Clinton campaigned for the Demcoratic ticket on Saturday, calling Mr McCain not a maverick but a 'mimic' of Mr Bush and saying the Arizona senator offered voters 'more of the same'.

Mr Obama sharply criticised Mr McCain's health care proposals on Saturday as 'radical', saying they could force millions of Americans to struggle to buy medical insurance. Republican officials accused Mr Obama of lying as the campaign took an ever nastier tone.

In a speech to thousands of sun-soaked Virginians at a waterside park in Newport News, Mr Obama said he would make health coverage more affordable to most Americans, paying for the subsidies largely by canceling the Bush administration's tax cuts for people making more than US$250,000 (S$362,000) a year.

Mr Obama said he would save money in the health care system by holding drug and insurance companies 'accountable for the prices they charge and the harm they cause'.

Mr McCain, meanwhile, spent Saturday at a resort hotel in Sedona, Arizona, preparing for his second of three debates with Mr Obama scheduled for Tuesday (Wednesday Singapore time) at Belmont University in Nashville, Tennessee.

The upcoming debate is critical because Mr McCain has dwindling chances to regain momentum. Mr McCain suggested to supporters that he would take the gloves off and go after Mr Obama more forcefully in Tuesday night's (Wednesday morning's, Singapore time) nationally televised debate.

Mr McCain's campaign apparently believes that making Mr Obama, who is seeking to become the first black US president, supremely unacceptable in voters' eyes may be the Republican's best - if not only - shot at winning the presidency. But that risks turning off voters if Mr McCain goes too far.

Mrs Palin got in a few early blows on Saturday when she said: 'Our opponent ... is someone who sees America, it seems, as being so imperfect, imperfect enough, that he's palling around with terrorists who would target their own country.'

She also said: 'This is not a man who sees America as you see America and as I see America.'

Nonetheless, Mrs Palin made the comments at three appearances in separate states, in Englewood, Colorado, and later in Carson, California, and Costa Mesa, California.

The Obama campaign called Mrs Palin's remarks offensive but not surprising in light of news stories detailing the McCain campaign's come-from-behind offensive.

'What's clear is that John McCain and Sarah Palin would rather spend their time tearing down Barack Obama than laying out a plan to build up our economy,' Obama campaign spokesman Hari Sevugan said in a statement.

Mrs Palin's incendiary comment was a reference to Obama's association with a former '60s radical, William Ayers, one of the founders of the Weather Underground. Its members took credit for bombings, including nonfatal explosions at the Pentagon and the US Capitol during the Vietnam War era. Mr Obama, who was a child when the group was active, has denounced Mr Ayers' radical views and activities.

While it is known that Mr Obama and Mr Ayers live in the same Chicago neighborhood, served on a charity board together and had a fleeting political connection, there is no evidence that they ever palled around. And it's simply wrong to suggest that they were associated while Mr Ayers was committing terrorist acts.

The escalated effort to attack Mr Obama's character dovetails with TV ads by outside groups questioning Mr Obama's ties to Mr Ayers, convicted former Mr Obama fundraiser Antoin 'Tony' Rezko and Mr Obama's former pastor, the Rev. Jeremiah Wright, who made remarks considered to be anti-American in his sermons.

Mr Ayers is a professor at the University of Illinois at Chicago. He and Mr Obama live in Chicago's Hyde Park neighborhood and served together on the board of the Woods Fund, a Chicago-based charity that develops community groups to help the poor. Mr Obama left the board in December 2002.

Mr Obama was the first chairman of the Chicago Annenberg Challenge, a school-reform group of which Ayers was a founder. Mr Ayers also held a meet-the-candidate event at his home for Mr Obama when Mr Obama first ran for office in the mid-1990s.

Mr Obama aides said they long planned to focus on economic issues in the final weeks of the race, but the debate over the government's US$700 billion (S$1 trillion) financial bailout focused voters on such concerns more than they could have imagined.

The push on health care is an opportunity to raise the debate on a pocketbook issue that voters rank near the top of their concerns.

According to an AP-Yahoo News poll taken last month, 78 per cent of voters rate health care as at least a very important issue, which puts it behind the economy in a group of second-tier issues along with Iraq and terrorism.

Mr Obama's criticism of Mr McCain's health care plan was echoed by his campaign in four new television ads, four separate mailers targeted to swing state voters, radio commercials and events in every battleground state.

In Virginia, Mr Obama devoted at least half his speech to criticising McCain. The Republican nominee has proposed to tax the health benefits that 156 million people get through the workplace as income. In exchange, McCain would give tax credits to help pay for insurance - US$2,500 for individuals and US$5,000 for families, paid directly to the insurer they choose.

Mr Obama said that under Mr McCain's plan, younger, healthier workers would buy cheaper insurance outside the workplace, leaving an older, sicker pool to drive up the cost of the employer-based system.

'As a result, many employers will drop their health care plans altogether,' Obama said. 'And study after study has shown, that under the McCain plan, at least 20 million Americans will lose the insurance they rely on from their workplace.'

He called Mr McCain's plan 'so radical, so out of touch with what you're facing, and so out of line with our basic values'.

Doug Holtz-Eakin, Mr McCain's senior policy adviser, said the Republican's plan to offer a tax credit in exchange for taxing employer-paid health benefits would be a net plus for all but the most wealthy Americans.

Republican National Committee spokesman Alex Conant responded: 'Barack Obama is lying about John McCain's plan to provide more Americans with more health care choices. Obama's plan only offers more government, while McCain's plan offers more choices.' -- AP