The Keystone XL would tap into the second biggest petroleum reserves on Earth. If it had been approved, it would run from Hardisty, Alberta, to Port Arthur, Texas. The $7 billion, 830,000-barrel a day project would go from Canada, through the Great Plains, crossing six states and ending in Texas. At left, an open pit mine in Fort McMurray, Alberta.

1. The oil sands deposit is massive — and so is the pipeline The Keystone XL would tap into the second biggest petroleum reserves on Earth. If it had been approved, it would run from Hardisty, Alberta, to Port Arthur, Texas. The $7 billion, 830,000-barrel a day project would go from Canada, through the Great Plains, crossing six states and ending in Texas. At left, an open pit mine in Fort McMurray, Alberta. Michael S. Williamson/The Washington Post

A big issue before President Obama is a proposal to approve a pipeline carrying fuel from Canada’s oil sands through America’s heartland to Texas. What’s at stake? Here’s a quick overview from “Down the Line: A Journey Along the Controversial Pipeline and Into America’s Energy Frontier.’’

A big issue before President Obama is a proposal to approve a pipeline carrying fuel from Canada’s oil sands through America’s heartland to Texas. What’s at stake? Here’s a quick overview from “Down the Line: A Journey Along the Controversial Pipeline and Into America’s Energy Frontier.’’

Secretary of State John F. Kerry, a prep school and college hockey player, surely knows how a stalemated game between two determined teams can end quickly with a single, critical call in the final moments.

Kerry picked up the referee’s whistle Friday, when the State Department issued its final environmental impact statement on the proposed Keystone XL pipeline project. His call in the months ahead, which will be made at least as much by President Obama, will determine whether the proposed $5.4 billion oil pipeline is in the national interest and whether it will be constructed after a years-long standoff between environmentalists and the oil industry.

“This is the gut-check moment,” Bill McKibben, co-founder of 350.org, said during a telephone news conference held Friday afternoon by some of Keystone’s most prominent foes in the environmental movement.

That means that neither side intends to ease up on Kerry, who has spent his career battling climate change. The 1,179-mile northern leg of the pipeline has become the most visible symbol of human-induced global warming that environmental activists are fighting, and they have promised to redouble their efforts as Kerry considers his decision.

At Friday’s news conference, Michael Brune, executive director of the Sierra Club, promised that anti-Keystone vigils will be held across the country this week and opponents will continue to offer public comment through the official government process. About 1.5 million public comments were filed before the report was issued. Other activists promised e-mails and phone calls to the State Department.

View Graphic Map of the Keystone XL pipeline.

Opponents will turn out in force if a public hearing is held, Brune said. If not, there will be “major public rallies and protests,” and environmentalists will be working hard for their friends — and against pipeline supporters — during mid-term election campaigns.

About a year ago, on Feb. 12, 48 activists, including Brune, were arrested in a protest at the White House. Keystone foes claim that tens of thousands of people have signed up to participate in future acts of civil disobedience.

Neva Goodwin, co-director of the Global Development and Environment Institute at Tufts University and a contributor to Kerry’s past campaigns, said she will be opposing the pipeline in another way.

“I’m working with an informal network of political donors that will be pushing Kerry to do the right thing,” said Goodwin, a great-granddaughter of John D. Rockefeller, the founder of Standard Oil.

Keystone supporters adopted a posture Friday that the report once again showed that the pipeline should be built and that it is time to get on with it.

“Let’s get this done. It’s time to bring over five years of regulatory review to an end and build this critical new piece of North American energy infrastructure,” Russ Girling, president and chief executive of TransCanada, which wants to build the pipeline, said in a statement.

“The benefits to the U.S. and Canada are clear,” Joe Oliver, Canada’s minister of natural resources, said in a separate statement. “We await a timely decision on this project.”

Friday’s report concluded that construction of the project would not significantly alter the level of greenhouse-gas emissions. But officials cautioned that they still would be assessing whether the pipeline, which would carry as much as 830,000 barrels of Canadian oil to U.S. refineries each day, fits with Obama’s overall climate strategy.

Eight federal agencies have the right to review Kerry’s decision. If even one objects, Obama must make the final call. For the president, who counts environmentalists among his most critical supporters, the game’s final minutes could be coming soon.

“I think it’s incumbent now on climate activists around the country and around the world to really let this president know this is about his climate legacy,” said Erich Pica, president of Friends of the Earth. “If he approves this pipeline, he reduces what little credibility he has to the rest of the world in showing that the U.S. is going to be a climate-change leader.”

Juliet Eilperin contributed to this report.