The economically battered Midwestern state is once again a major electoral battleground as Mrs Clinton digs in her heels for possibly a last stand against rival Obama.

The two candidates will face off in a debate in Cleveland later today that is expected to focus on the best solution to the sub-prime mortgage crisis in the United States and the decline of the manufacturing sector - only neighbouring Michigan fared worse in job losses and home foreclosures last year.

While Ohio offers fewer delegates than Texas in the March 4 primaries - 141 to 193 in Texas - it plays a critical role in the presidential election.

A key swing state, Ohio was the 'ground zero' of US presidential politics in 2004, when President George W. Bush beat Democratic Senator John Kerry with just 137,000 out of more than 5.6 million votes cast.

And since 1964, no American president has ever been elected without winning Ohio.

Ohio should have been an easy win for Mrs Clinton. She has the support and powerful statewide political operation of long-time ally Governor Ted Strickland and had been polling more than 20 points ahead in the predominantly white, blue-collar state.

But that lead has narrowed to seven points as Mr Obama won 11 nominating contests in a row and picked up major labour union endorsements.

On Sunday, Mrs Clinton lashed out at 'companies shamelessly turning their backs on Americans' by shipping jobs overseas, and railed that 'it is wrong that somebody who makes US$50 million (S$70 million) on Wall Street pays a lower tax rate than somebody who makes US$50,000 a year'.

In an appearance here on Sunday, she also mocked Mr Obama's hopeful rhetoric, declaring it is not the answer to fighting entrenched interests.

'I could stand up here and say, 'Let's just get everybody together, let's get unified, the sky will open, the light will come down, celestial choirs will be singing and everyone will know we should do the right thing and the world will be perfect',' she said to cheers and laughter.

'You are not going to wave a magic wand and have the special interests disappear.'

Mr Obama leads Mrs Clinton 1,374 to 1,275 delegates, said RealClearPolitics.com.

A total of 2,025 is needed to secure the party's nod, and much will hinge on the votes of super-delegates, party luminaries free to vote how they like at the party convention.

While the majority of Ohio voters see Mrs Clinton as the candidate best able to handle the issues which matter most to them - the economy and health care - Mr Obama held a 48 per cent to 37 per cent lead among Ohio Democrats when asked who has the best chance to win in November, according to a poll released at the weekend by ABC News and the Washington Post.

But a third of likely voters said they could still change their minds before the polls.

In Ohio, Mr Obama in turn blasted Mrs Clinton for trying to walk away from a long record of support for the North American Free Trade Agreement (Nafta), the deal with Mexico and Canada that he said has cost 50,000 jobs in the state.

One day after Mrs Clinton angrily accused him of distorting her record on Nafta in mass mailings, Mr Obama shot back, using passages from the former first lady's book and her own words.

'Ten years after Nafta passed, Senator Clinton said it was good for America,' he said. 'Well, I don't think Nafta has been good for America - and I never have.'

The trade agreement has long been unpopular in industrial Mid-western states such as Ohio, where critics blame it for lost jobs and shuttered factories, many of which once employed union workers who tend to vote Democratic.

ASSOCIATED PRESS, LOS ANGELES TIMES, AGENCE FRANCE-PRESS