The Democratic senator traveled to the industry heartland in Detroit to warn America could no longer sustain bloated energy consumption, unveiling a plan to encourage auto companies to build more fuel-efficient cars.

"The auto industry's refusal to act for a long time has left it mired in a predicament for which there is no easy way out," Obama said.

"But 'expensive to do' is no longer an excuse for failure to do," Obama said, becoming the latest presidential candidate to call for energy policy reform.

Oil dependency corrupts emerging democracies, jeopardized US security and harms the planet, said Obama, vying with Senator Hillary Clinton for top billing in the Democratic White House field.

"For the sake of our security, our economy, our jobs and our planet, the age of oil must end in our time," he told the Detroit Economic Club, also noting that auto workers union has also resisted change.

"For years, while foreign competitors were investing in more fuel-efficient technology for their vehicles, American automakers were spending much of their time investing in bigger, faster cars."

The result was, Obama said, that while US cars typically averaged around 27.5 miles (44 kilometers) per gallon.

Japanese vehicles had surpassed American standards at an average of 45 miles (72 kilometers) to the gallon, he said.

He pledged to strike a bargain with auto manufacturers, by offering tax incentives to help them upgrade plants to produce more fuel-efficient vehicles and help defray healthcare costs for workers if firms invested in new age technology.

American consumers would also get tax breaks to encourage them to buy more fuel efficient, US-produced cars, he said.

Clinton Monday meanwhile campaigned in Obama's home town of Chicago, as a poll by the Rasmussen organization suggested she had recaptured her lead in the race.

The New York Senator had the support of 34 percent of likely Democratic voters, compared to Obama's 26 percent. The same organization reported on April 30 that Obama had a 32 to 30 percent lead in the race.

Clinton has proposed putting huge profits of oil firms into a strategic fund to invest in new kinds of energy and technologies.

Another top tier Democratic candidate, John Edwards, has call for investment in clean, renewable energy and bio fuels, and a new generation of efficient cars and trucks.

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