President Obama faces new pressure to produce results on climate change after he announced in his inaugural address that he would make the issue a top priority for his second term. But staunch Republican opposition to sweeping environmental laws will force the president to go through his Environmental Protection Agency, rather than Congress, to implement the changes he promised, officials on both sides of the debate said.

Obama has vowed to reduce greenhouse gases and to slow warming temperatures, saying a failure to do so "would betray our children and future generations."

And while environmentalists applauded the president's pledge, they are encouraging him to use his executive powers rather than Congress on issues like stricter limits on carbon emissions. The EPA last year recommended limited carbon emissions from new power plants, but advocates now want Obama to expand that rule to include existing power plants, as well.

"He's basically giving marching orders to whoever he puts in charge at the EPA," Frank O'Donnell, president of the nonpartisan Clean Air Watch, said of the president's new tone. "Legislation is pretty unlikely, given the makeup of Congress. Setting forth emissions standards for existing coal-burning power plants -- that's the mother of all climate rules."

The president is looking for a new leader at the EPA after Lisa Jackson announced that she would step down following Obama's State of the Union address in February.

White House press secretary Jay Carney refused to specify what kinds of climate-change legislation Obama might pursue. He indicated that the president still supports the cap-and-trade bill that died on Capitol Hill during his first term but didn't say whether Obama would push for it again.

"We also want an 'all of the above' energy strategy that will lower costs, reduce our dependence on foreign oil and improve our environment," Brendan Buck, a spokesman for House Speaker John Boehner, R-Ohio, told The Washington Examiner. "Unfortunately, the president's approach to the issue would destroy, rather than create, jobs."

The White House points to tens of billions of dollars in stimulus funding for green projects and tighter fuel-economy standards for vehicles as proof of the president's commitment to tackling climate change. Yet, when a cap on carbon emissions died on Capitol Hill, the president -- facing a tough re-election battle -- didn't fight for it.

"He didn't run on green issues at all; he can't claim a mandate on them," said Kenneth Green, senior director of energy and natural resource studies at the Fraser Institute.

Obama already faces his first test of his second term on the environment. Nebraska Gov. Dave Heineman on Tuesday approved an alternate path for the Keystone XL oil pipeline through the state. The pipeline would deliver oil from Canada to Texas but has pitted Obama's union allies, who welcome the new jobs, against the president's environmental supporters.

The Obama administration, which had already delayed the construction of the northern portion of the pipeline, said Tuesday that it would again push back the decision -- this time until April.

"If Obama really meant what he said in the inaugural, he will say no [to Keystone]," O'Donnell said.

Meanwhile, Republicans are pushing the Obama administration to approve the pipeline.

"With our energy security at stake and many jobs in limbo," Boehner said, "[Obama] should find a way to say yes."