"We will make it clear to the world that America is ready to lead," he said as he signed his first two Presidential Memoranda aimed at getting the US on the path to energy independence, a key step in preventing the US "from being held hostage" to hostile regimes and the threat of global warming

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"To protect our climate and our collective security, we must call together a truly global coalition. I've made it clear that we will act, but so too must the world," Obama said.

"That's how we will deny leverage to dictators and dollars to terrorists," he said. "And that's how we will ensure that nations like China and India are doing their part, just as we are now willing to do ours."

"It's time for America to lead, because this moment of peril must be turned into one of progress," he said, describing America's dependence on oil as "one of the most serious threats that our nation has faced".

"It bankrolls dictators, pays for nuclear proliferation, and funds both sides of our struggle against terrorism," he said. "It puts the American people at the mercy of shifting gas prices, stifles innovation and sets back our ability to compete."

"These urgent dangers to our national and economic security are compounded by the long-term threat of climate change, which if left unchecked could result in violent conflict, terrible storms, shrinking coastlines and irreversible catastrophe," Obama said.

But "America will not be held hostage to dwindling resources, hostile regimes, and a warming planet", he declared.

Now is the time to meet the challenge at this crossroad of history by choosing a future that is safer for our country, prosperous for our planet, and sustainable, he said.

In what he called "a down payment on a broader and sustained effort to reduce our dependence on foreign oil", Obama directed the Transportation to establish higher fuel efficiency standards for carmakers' 2011 model year.

The standard, known as Corporate Average Fuel Economy (CAFE), was established in 1975 in the wake of the Arab Oil Embargo.

The second memo paves the way for California and more than a dozen other states to raise emissions standards above and beyond the national standard. They'd asked to do so before, but the Bush administration had denied the request.

"Instead of serving as a partner, Washington stood in their way," Obama said. "The days of Washington dragging its heels are over."