US President Barack Obama has announced a series of measures aimed at reducing the country's dependence on foreign oil and cutting the long term threat of climate change.
The president cleared the way for the government to allow states to set stricter limits on greenhouse gas emissions from cars.
He told the US Environmental Protection Agency to reconsider California's request, denied under President George Bush, that would allow it to impose stricter limits on vehicle carbon dioxide emissions.
As many as 18 other states have indicated they may follow California's lead, putting in place emissions standards that are tougher than federal requirements.
The president also directed the Department of Transportation to move forward with setting vehicle fuel efficiency standards for 2011 by March, giving car manufacturers an 18 month period to impose them.
Mr Obama instructed the US government in general to become more energy efficient.
"It will be the policy of my administration to reverse our dependence on foreign oil," he said, adding previous administrations had made similar goals.
"We need more than the same old empty promises. We need to show that this time it will be different," he said.
The US State Department is expected to name Todd Stern, a senior White House official under former President Bill Clinton, as its climate change envoy, Reuters reports.
Mr Stern coordinated the Clinton administration's Initiative on Global Climate Change from 1997 to 1999 and acted as the senior White House negotiator in the Kyoto negotiations on climate change.