It’s crunch time in the fight over constructing the Keystone XL oil sands pipeline.

Both sides believe a decision by President Obama could come by the end of the year, making the next few months critical for lobbying and messaging efforts.

Opponents plan a burst of demonstrations and other events across the country to rally environmental pressure on Obama to reject the Alberta-to-the-Gulf-Coast pipeline.

Supporters are also campaigning, with the American Petroleum Institute (API) promoting its message that Keystone’s construction will create jobs, with rallies in more than a dozen “priority states” in the coming months, API spokeswoman Sabrina Fang told The Hill.

The State Department is reviewing the project and says there is no timetable on a decision.

But Obama told lawmakers in March that a decision would be coming in a matter of months, not years, raising expectations that the administration will act before the end of the year.

The State Department is reviewing 1.2 million comments to a draft environmental report it performed on the project. Once that report is finalized, a 90-day period for the department to determine whether Keystone is in the national interest will be triggered, followed by two weeks for Obama to render his decision.

Keystone opponents believe momentum has flipped to their side and think Obama — once seen as likely to approve the project — will now reject it.

“For months, and even years, the conventional wisdom was that approval was imminent. Pipeline opponents knew that wasn’t the case, and now the conventional wisdom has finally come around,” Rachel Wolf, a spokeswoman with the All Risk, No Reward Coalition, told The Hill in an email.

Wolf’s optimism comes in part from Obama’s recent rhetoric.

The president has embraced some of the talking points of Keystone detractors since his climate speech in June, raising hopes of environmentalists that he is leaning against the project.

“It’s certainly encouraging that he’s picked up on many of the arguments we’ve been making a long time,” Daniel Kessler, a spokesman with climate advocacy group 350.org, told The Hill. “More importantly, he’s picking up on the argument that we need to do something extreme on climate change right now.”

Obama has publicly questioned the jobs impact of Keystone in recent speeches. He also remarked that it wouldn’t have much of an effect on gasoline prices and suggested much of the oil sands it would transport are destined for export.

Obama also said he would oppose Keystone if it “significantly exacerbates” carbon pollution, something the project’s opponents say is a certainty.

Keystone backers say the pipeline already passes Obama’s greenhouse gas test, as the draft State environmental report said it wouldn’t substantially boost emissions.

Opponents, however, say the report is flawed and are asking for a redo.

While Obama’s emissions comments were more open to interpretation, the ones he made on jobs and gas prices were viewed as direct shots at Keystone supporters. That has raised the furor of Republicans, centrist Democrats, industry groups and labor unions that support Keystone, bringing tensions to a new level.

The jobs claims — Obama said they’d be a “blip” in the employment picture — were met with fierce opposition from Keystone boosters. They said Obama’s figures low-balled that of his own State Department, and urged him to reassess his numbers.

Keystone proponents have touted polling that shows a majority of Americans of all stripes back the project. And they’ll press that point further in the coming weeks, Matt Dempsey, a spokesman with industry group Oil Sands Fact Check, told The Hill.

Oil Sands Fact Check is planning a campaign designed to convey that data to news publications, including those inside the Beltway, to counter the “vocal minority” of activists, Dempsey said.

“It’s not reaching out beyond the Beltway. It’s not reaching out to anyone who’s already made up their minds,” Dempsey said of Keystone opponents’ arguments.

But those opponents are fixing to get louder.

The Natural Resources Defense Council is spearheading a Wednesday media call to make the case that mitigating the carbon emissions of Alberta’s oil sands aren’t enough to offset the amount Keystone would facilitate.

The Sierra Club hopes to press the Keystone issue during a pair of Aug. 22 events Vice President Biden is scheduled to attend in New England, and is coordinating other events as well, spokesman Trey Pollard told The Hill.

Kessler told The Hill on Monday that his group is planning a nationwide “Day of Action” for Sept. 21 that will encompass “hundreds, if not thousands” of demonstrations. It’s also working on one for November with partners in Canada, he said, noting that 350.org usually orchestrates just one such event each year.

And the Other 98%, a left-leaning group, will hold a protest at Keystone builder TransCanada Corp.’s Houston office next month. A demonstration in Boston will follow in November.

Despite the activity, groups warned that predicting the decision date is an inexact science of sorts.

“The decision could still be months away,” Wolf said. “But it would be accurate to say that pipeline opponents feel the momentum.”