President Obama said Tuesday he will approve the Keystone XL pipeline only if it does not substantially increase greenhouse gas emissions — a surprise announcement ambiguous enough to leave both sides in the fight thinking they’d heard good news. [WATCH VIDEO]

“Our national interest will be served only if this project doesn’t significantly exacerbate the problem of carbon pollution,” Obama said in speech laying out his second-term climate agenda, including greenhouse gas emissions for power plants.

“The net effects of the pipeline’s impact on our climate will be absolutely critical to determining whether this project can go forward.”

{mosads}Republicans backing TransCanada Corp.’s pipeline, which would bring oil sands crude from Alberta to Gulf Coast refineries, pointed to a draft State Department analysis in March that concluded the project would have little effect on how quickly oil sands production increases.

“The standard the president set today should lead to speedy approval of the Keystone pipeline,” said Brendan Buck, a spokesman for House Speaker John Boehner (R-Ohio).

The consulting firm ClearView Energy Partners, in a note, said Obama “left the door open to a final approval.”

“The State Department could determine on its own that GHG [greenhouse gas] impacts do not ‘significantly’ exacerbate the nation’s GHG emissions levels or are sufficiently modest relative to other reductions,” ClearView wrote.

“Attaining the vague notion of insignificance might require action from project sponsors – voluntary or otherwise – but seems well within the realm of reason given the State Department starting point,” the company said.

Keystone’s foes said they were heartened because they do not believe there is any way the pipeline will pass Obama’s test.

Environmentalists argue that the expansion of carbon-intensive oil sands development is heavily dependent on major additions to pipeline capacity.

“The only way this project passes the president’s test is to claim that just as much tar sands crude would be produced without the pipeline, that there might be some other way to ship it out of Canada. That can’t happen, as more and more evidence affirms,” said Susan Casey-Lefkowitz of the Natural Resources Defense Council.

“The president is saying what the science has always demanded. It’s encouraging news for certain,” said Bill McKibben, founder of the group 350.org.

The studied ambiguity in Obama’s remarks was reminiscent of his recently announced policy on drones, which also left people guessing what the White House would do and offered the president significant flexibility.

Obama delivered the remarks at Georgetown University on a sweltering summer day, which he used to highlight the need for action on climate change.

The wide-ranging speech made the case for actions that don’t need approval in Congress and underlined Obama’s determination to tackle the issue during the rest of his term on his own.

Central to Obama’s plan is a directive for the Environmental Protection Agency to craft carbon regulations for existing power plants, which create about a third of U.S. greenhouse gas emissions, largely due to coal.

The agenda also requires the EPA to complete planned carbon rules for new plants.

Republicans have long argued Obama is waging a war against coal, and they received an unexpected assist Tuesday from a member of an outside panel advising the White House on science.

Harvard professor Daniel P. Schrag told The New York Times that “a war on coal is exactly what’s needed,” but that Obama would never say so publicly because of politics.

Republicans seized on the remarks, while coal-country Democrats pounced on Obama’s proposals.

“It’s clear now that the president has declared a war on coal,” Democratic Sen. Joe Manchin (W.Va.) told reporters. “It’s simply unacceptable that one of the key elements of his climate change proposal places regulations on coal that are completely impossible to meet with existing technology.”

Manchin said the president’s plan would have “disastrous consequences” for the economy.

“These policies punish American businesses by putting them at a competitive disadvantage with our global competitors,” Manchin said. “And those competitors burn seven-eighths of the world’s coal, and they’re not going to stop using coal any time soon.”

Sen. John Barrasso (R-Wyo.) warned Republicans would force a vote on Obama’s climate plan to put Senate Democrats on the record.

“We will attach an opportunity to have every senator on the record to some bill moving through the Senate, either in the form of an amendment, a sense of the Senate [resolution], to see if Democrats are going to stand by the people in their home states who want affordable energy and jobs, or if they will stand by a president who doesn’t seem to care that much about affordable energy and jobs,” said Barrasso, a member of the GOP’s leadership team.

Beyond the EPA, Obama’s plan includes a new round of fuel economy standards for heavy trucks, an expanded Interior Department commitment to develop renewable energy on federal lands and making billions of dollars of Energy Department loan guarantees available for low-emissions coal projects.

Environmental activists were effusive in praising Obama’s speech, in which the president also aggressively attacked skeptics of climate change.

“We don’t have time for a meeting of the flat-Earth society,” Obama said. “Sticking your head in the sand might make you feel safer, but it’s not going to protect you from the coming storm.”

Writing on his blog, former Vice President Al Gore called it “historic” and “the best address on climate by any president ever.”

League of Conservation Voters President Gene Karpinski called it “the most comprehensive and ambitious administrative plan proposed by any president.”

Justin Sink and Jonathan Easley contributed.