Washington - US presidential candidates Barack Obama and John McCain clashed on free trade and its value to a sputtering US economy during their last television debate of the election campaign.

Republican nominee McCain said Wednesday that opening up trade would foster millions of jobs in the United States but acknowledged that re-education programmes for US workers losing their jobs would have to be improved. He called for an end to tariffs on sugar cane-based ethanol from Brazil to help the United States diversify its energy sources.

Democratic rival Obama said he was a free-trade supporter but held US workers' interests at heart. He touted a pending deal with South Korea, which would allow struggling US automakers sell more of their goods on the Asian market.

"They are sending hundreds of thousands of South Korean cars into the United States," Obama said. "... We can only get 4,000 to 5,000 into South Korea. That is not free trade."

Obama criticized President George W Bush's administration for a policy that "any trade agreement is a good trade agreement."

McCain focused on the Colombian free-trade agreement pending before Congress, calling it a "no-brainer" that would help create jobs in the United States and aid a key Latin American ally in its fight against drug trafficking.

He accused Obama of wanting to renegotiate the North American Free Trade Agreement and slammed his Democratic rival for what he deemed protectionist policies.

"Senator Obama wants to restrict trade and he wants to raise taxes, and the last president of the United States that tried that was Herbert Hoover, and we went from a deep recession into a depression," McCain said.

Obama countered that all trade deals had to include protections for US workers, for the environment and for the "human rights" of labour union members who have been targeted for assassination in Colombia.

"We've got to have a president who is going to be advocating on behalf of American businesses and American workers, and I make no apology for that," Obama said.

Trade has played a small part in the US election to date but could take on a greater role in the final three weeks of the campaign ahead of the November 4 election. Any and all economic issues have come under a greater microscope recently amid the prospects of a recession in the United States. (dpa)