As the totemic fight over the Keystone XL oil pipeline enters its crucial, final phase, backers and detractors of the project have escalated their pressure on President Barack Obama, who has the final say but remains noncommittal.

Environmental activists have set out to generate 1 million opposing public comments to the State Department, which is in the process of deciding whether the pipeline is in the national interest. Opponents have engaged in civil disobedience and mass protests during a multiyear campaign to block the project, which has emerged as a flash point for environmental lobby frustration. They’re even trailing Obama with mini-protests at his stops at home and abroad.

The pipeline’s backers are also mounting demonstrations, including a 400-person labor-led rally last week in St. Paul, Minn. Pipeline backers include the oil and gas lobby, labor unions representing construction workers, the Canadian government and TransCanada Corp., which proposed the pipeline network from Canada to the Gulf of Mexico.

Both sides have zeroed in on April 22 as a banner day. That’s when the State Department closes the public comment period for a draft environmental impact statement released this month. It also happens to be Earth Day, and coincides with the annual legislative conference of the AFL-CIO’s Building and Construction Trades Department, an event that will bring thousands of pro- pipeline labor organizers to Washington.

“This is the last window to get the trains off the track,” said Becky Bond, president of the CREDO super PAC, whose affiliate CREDO Action has already generated more than 100,000 public comments to the State Department. Led by the Sierra Club and the climate action organization 350.org, the anti-pipeline campaign has rallied hundreds of progressive groups behind the Tar Sands Coalition. Tar sands oil is controversial because it generates high levels of greenhouse gases when extracted.

On the surface, the four-year pipeline battle appears to be tilting TransCanada’s way. This month’s report from the State Department, released after numerous delays and failed attempts by congressional Republicans to speed up the process, essentially concluded that the pipeline would have little environmental effect.

“We have yet to see any objective study of this pipeline that says it shouldn’t be built,” said David Mallino, legislative director of the Laborers’ International Union of North America. “We wish this process had moved faster, but the process has yielded positive results.”

The real fight now may be over whether pipeline opponents, who regard the Keystone decision as a key test of Obama’s environmental commitment and legacy, will be able to win any consolation prizes from the administration.

“The indications are that this is heading towards approval, and they want to get something for it,” said Robert McNally, president of the independent consulting firm the Rapidan Group. Obama spotlighted the need for climate action in his inaugural and State of the Union speeches, possibly laying the groundwork for emissions limits on power plants or other carbon restrictions.

But environmentalists reject the notion that they’re angling for a trade off. “There is no trade. The reality is that we need to stop the Keystone XL pipeline from being built,” 350.org spokesman Daniel Kessler said.

The pipeline has handed the environmental movement a potent organizing tool. Even if the project goes through, the movement will gain steam, said Eddie Scher, senior communications strategist for the Sierra Club’s Beyond Oil Campaign. “Keystone XL is the front line in the fight over climate disruption,” he said, because it “is very tangible” and “has very local impacts in the places where the pipeline will run.”

The pipeline’s potential political fallout isn’t lost on the American Petroleum Institute, which has promoted the project as a jobs generator and is in the midst of a Washington-area print ad campaign delivering the message: “We Need it Now! Keystone XL is More than a Pipeline. It’s a Lifeline.”

“We are somewhat concerned in the broader scheme … if this is the way that we are going to have to deal with every infrastructure project,” API Executive Vice President Marty Durbin said. Obama sent mixed signals about the pipeline in a meeting with House Republicans last week and is expected to decide on the fate of the project by late summer.

“We’ve seen a fairly straightforward infrastructure proposal become a symbolic flash point,” said Elliot Diringer, executive vice president of the Center for Climate and Energy Solutions. “And it’s easy to see why. It’s a tangible project, where the president alone can make an up-or-down decision.”