Obama, who has kept energy reform high on his priority list since taking office in January, used Earth Day to tout the need for a US shift to less-polluting fuels and a concerted effort to reduce the nation's dependence on foreign oil.

"It is time for us to lay a new foundation for economic growth by beginning a new era of energy exploration in America," Obama told workers at a wind power technology plant in Iowa, the state that propelled his presidential campaign more than a year ago.

"The nation that leads the world in creating new energy sources will be the nation that leads the 21st century global economy. America can be that nation. America must be that nation."

US negotiators are preparing proposals for international climate talks to be held in Copenhagen in December, aimed at agreeing a pact to succeed the Kyoto Protocol, which sets limits on greenhouse gas emissions.

The US Congress may hold the key to the Obama administration's credibility at those talks. It is mulling legislation that would put a cap on carbon dioxide (CO2) and other greenhouse gas emissions, forming a so-called cap-and-trade system that is similar to the European Union's.

In Washington, senior Obama administration officials urged lawmakers to back the bill.

"There will be no new global deal if the United States is not part of it, and we won't be part of it unless we are on track in enacting our own domestic plan," Todd Stern, the top US climate negotiator, told the Senate Foreign Relations Committee.

"Unless we stand and deliver by enacting strong, mandatory nationwide climate and energy legislation, the effort to negotiate a new international agreement will come up short."

Washington is hosting a meeting of big economies next week to help forge a climate deal. In a reference to his predecessor, former Republican President George W Bush, Democrat Obama said the days of a slow US response to global climate talks were over.