The Obama administration may reassess the proposed route for a major oil pipeline that would stretch from northern Canada to the Gulf Coast, according to sources familiar with the deliberations, a move that could delay the contentious permitting process for more than a year.

The State Department has identified a route that traverses six states — and runs above Nebraska’s Ogallala aquifer — as its “preferred alternative,” among more than a dozen possibilities. But opposition has mounted in Nebraska and elsewhere along that path. The Nebraska legislature is in special session to consider options for influencing the pipeline’s route.

For more than three years, the State Department has been examining whether to grant TransCanada’s proposal to construct and operate a 1,700-mile pipeline that would ship crude extracted in Canada’s oil sands region to U.S. refineries.

Proponents of the Keystone XL extension say it will generate badly needed jobs in the United States and ensure a steady supply of oil from a friendly ally. But environmentalists and an eclectic group of ranchers, farmers and other opponents say the pipeline could threaten habitat along its route and could destabilize the climate because the oil it would transport is especially energy-intensive to extract.

The State Department is scheduled to meet Thursday with several officials who have helped oversee the permitting process, sources said. The group is expected to discuss whether to formally reconsider the project’s route, which would delay any final permit decision while the government conducted a new environmental assessment. People familiar with the process say this could take a year or more.

In a news briefing Wednesday, department spokesman Mark Toner said a rerouting of the pipeline is “one of many issues that we have discussed that were raised during these public hearings that we held, and all of those issues are currently under review as we move forward.”

Although the agency for months has said it intends to conclude the process by the end of the year, Toner added, “We’re not going to be held to any artificial deadline.”

Jack Gerard, president of the American Petroleum Institute, said the proposal has been through “an unprecedented review” that has lasted longer than the review for any other oil pipeline. Since it has undergone a full environment review, he said, “the only motivation for any shift in policy is purely political considerations.”

TransCanada spokesman Terry Cunha wrote in an e-mail that a further delay would have serious consequences for the United States. “If Keystone XL dies, Americans will still wake up the next morning and continue to import 10 million barrels of oil a day,” he wrote. “Much of that oil will flow from repressive nations, without the benefit of thousands of jobs and long-term energy security. That would be a tragedy.”

But environmentalists said President Obama should reject a project that would perpetuate the nation’s dependence on fossil fuels.

“We need the president to take charge and fulfill his commitments to break our addiction to oil and reduce the pollution that is heating our planet,” said Jeremy Symons, senior vice president at the National Wildlife Federation.