(WASHINGTON) -- It's shaping up to be one of the trickiest decisions President Obama will have to make early in his second term: whether to approve construction of the 1,700-mile Keystone XL oil pipeline, stretching from Alberta, Canada, to Oklahoma.
Nebraska Gov. Dave Heineman, a Republican, on Tuesday endorsed a revised pipeline route through his state, removing a final hurdle for the $5 billion project on the state level. Governors and congressional delegations from the four other states it crosses have already pressed for federal government approval.
The fate of the project now rests squarely with the Obama administration, which has the final say because it crosses an international boundary.
For the White House, the issue is a perfect storm of competing interests: the promise of thousands of new construction jobs and potential for cheaper energy, but with stiff opposition from environmental groups that say the pipeline would mean a toxic injection of greenhouse gases into the atmosphere and heightened risk of destructive spills.
The State Department, which is finalizing an environmental review, is expected to present the president with its recommendations by the end of March. "I don't want to get ahead of that process," White House press secretary Jay Carney said Tuesday when asked about the decision.
Previous versions of the pipeline application, which were ultimately tabled over environmental concerns raised by Nebraska, appeared poised for federal approval. There was no public opposition to the plan from the Environmental Protection Agency or the Pipeline and Hazardous Materials Safety Administration, which had reviewed the plans.
President Obama even visited a portion of the Keystone pipeline in March 2012 to urge expedited construction of a southern portion that didn't cross through Nebraska. So far, the project has employed 4,000 workers, according to TransCanada, which operates the pipeline. When it's completed later this year, it will carry 700,000 barrels of oil per day from Oklahoma to the Gulf Coast, the company said.
"We need to encourage domestic oil and natural gas production. We need to make sure that we have energy security and aren't just relying on Middle East sources," Obama said on a visit to remote Cushing, Okla.
"But there's a way of doing that and still making sure that the health and safety of the American people and folks in Nebraska are protected, and that's how I'll be measuring these recommendations when they come to me," he said at the time.
Now that Nebraska's political leaders have approved the northern portion of the pipeline plan, from Canada to Oklahoma, members of Congress are heaping pressure on Obama to follow suit.
"He and he alone stands in the way of tens of thousands of new jobs and energy security," said House Speaker John Boehner. "Every state along the proposed route supports this project, as does a bipartisan coalition in Congress and a majority of Americans."
TransCanada estimates the Keystone XL project will support 9,000 U.S. jobs through early 2015.
Fifty-three senators -- including nine Democrats -- are also joining the chorus, sending a letter to the White House on Wednesday requesting a meeting with Obama to discuss the issue and urging him to expedite approval. Hoeven, Democratic Sen. Max Baucus of Montana, and 16 others signed a letter to Obama calling on him to approve the deal now that Nebraska's concerns have been resolved.
But Obama faces significant pressure from an engaged environmental lobby to block the plan, particularly in light of his groundbreaking comments on climate change in his second inaugural address.
"You cannot say the words the president did in his inaugural address, and then turn around and approve the pipeline," said Jane Kleeb with BOLD Nebraska, an advocacy group opposed to the plan. "This much is as crystal clear as the Ogallala Aquifer is without this risky export tar sands pipeline."
Environmental advocates say the refining of tar sands to oil is particularly dangerous and dirty, producing plumes of gases that contribute to global warming. They also note the destruction of natural landscape in the construction process and potential for habitat-destroying spills.
Activists plan a major rally against the pipeline on the National Mall later next month.
"Together we'll send the message loud and clear," said leading environmental activist and author Bill McKibben on his blog, "'If you're serious about protecting future generations from climate change, stop the Keystone XL tar sands pipeline. If you can do that, Mr. President, we can all work together to help build a climate legacy that will be a credit to your critical eight years in office.'"
With the election in the rearview mirror and no pressure of a campaign for a second term, Obama may feel freer to buck the protests from environmental and progressive groups, particularly since other key constituencies in his base -- including labor unions -- are for the pipeline plan.
"My general attitude is what is best for the American people? What's best for our economy both short term and long term? But also, what's best for the health of the American people?" Obama explained of his thinking during a November 2011 interview on the pipeline plan, before he later tabled the decision for further review.
"I recognize all the political pressure the president faces," Boehner said Tuesday, "but with our energy security at stake and many jobs in limbo, he should find a way to say yes."
Copyright 2013 ABC News Radio