INDIANAPOLIS, US - WHITE House hopeful Barack Obama sought on Saturday to wrest away rival John McCain's key campaign theme, casting himself as the 'Straight Talk' candidate who is willing to level with voters about tough choices facing the country.

In recent days, Democrat Obama has been hammering the Arizona senator and presumptive Republican nominee over his plan to offer voters a temporary 'holiday' from the petrol tax.

Mr McCain says the proposal is needed give cash-strapped consumers relief from surging costs at the fuel pump during the busy driving season.

In addition to bashing Mr McCain over the issue, Mr Obama also criticized New York Senator Hillary Clinton, his Democratic opponent who also backs the tax holiday. The two face voting contests on Tuesday in North Carolina and Indiana, the next steps in their protracted struggle for the right to run against Mr McCain in the November election.

Mrs Clinton told a rally in Wake Forest, North Carolina, 'These prices that are going up from...gas prices, to grocery prices, are really taking a big chunk out of people's disposable income.'

'I think that it's imperative that we try to obtain some immediate relief,' she added.

In a speech that was part of an effort by Mr Obama to retool his message after a series of setbacks and amid sliding poll numbers, he ridiculed both Mr McCain and Mrs Clinton over the gasoline tax idea.

'It's a shell game - literally,' Mr Obama, an Illinois senator, told an audience at an Indianapolis high school. 'If we want to take a permanent holiday from our oil addiction, we can finally get serious about energy independence.'

He said that his own proposals for raising car fuel-mileage standards and spurring investment in energy-efficient technology were better ways to 'free ourselves from the whims of Middle East dictator' and give consumer longer-lasting relief at the pump.

MCCAIN RESPONDS

Mr Obama did not specifically use the word 'Straight Talk' - an expression that Mr McCain has used for years to describe the maverick style of politics he has become known for over many years.

But his speech marked a clear attempt to suggest that he - not Mr McCain - was the candidate who was willing to stand up and take principled stances even when they are not popular.

In response, the McCain campaign sought to criticise Mr Obama's economic proposals and paint him as a tax raiser because of his proposal to increase taxes on dividends and capital gains.

'Barack Obama's repeated pledges to raising taxes on millions of small investors and expiring tax relief that is at work in family budgets shows he just doesn't understand the American economy,' said McCain spokesman Tucker Bounds.

Mr Obama remains the front-runner in the Democratic race. But his campaign has been hit by a slew of difficulties over the past several weeks that Mrs Clinton has seized on as evidence that he would be the weaker candidate to take on Mr McCain in the general election.

Those struggles include public comments from Obama's former pastor, Reverend Jeremiah Wright, who repeated earlier charges that the Sept 11 attacks were retribution for US foreign policy and that the US government had a hand in spreading AIDS to harm blacks.

Mr Obama this week made a break with the minister, who he has known for two decades and who officiated his marriage and baptized his two children. - REUTERS