Environmentalists hoping to block a proposed underground oil pipeline that would snake 1,700 miles from Canada to the Gulf of Mexico have pinned their hopes on an unlikely ally — the conservative state of Nebraska.

Few states are as red as Nebraska, which hasn’t supported a Democratic presidential candidate since 1964. But opposition to the Keystone XL pipeline has risen steadily since the project was proposed three years ago.

The reason: Fears of contaminating the Ogallala Aquifer, a vast subterranean reservoir that spans a large swath of the Great Plains and provides water to much of Nebraska as well as seven other states. Opponents have grown to include Nebraska’s conservative governor and two U.S. senators, a Republican and a conservative Democrat.

Many in the public are hostile to the idea, too. When a pipeline company logo was displayed on a stadium screen during a recent Nebraska Cornhuskers game, boos rained down from the crowd of 85,000. The university agreed to stop running the ads.

Damon Moglen, a spokesman for the Washington-based environmental group Friends of the Earth, called Nebraska “the key battleground” over the proposal.

Both sides of the debate will have a final chance to make their case this week when public hearings are held in Lincoln and Atkinson, a small town in northern Nebraska. Similar meetings are scheduled in other states that would be crossed by the pipeline.

“We’re in the fourth quarter of this game,” Moglen said. “The question is, can the home team up its game and win?”

In addition to approval from affected states, the international project needs backing from the State Department, which expects to decide the matter by the end of the year. Department leaders are likely to attend some of the hearings.

“We see these as listening sessions,” said Kerri-Ann Jones, the assistant secretary of state in charge of the Bureau of Oceans and International Environmental and Scientific Affairs. “We want to listen and hear what people have to say.”

If built, the 16-inch steel pipe would carry oil extracted from tar sands in Alberta through Montana, South Dakota, Nebraska, Kansas and Oklahoma to refineries in Texas.

Other states have mostly accepted a promise from the pipeline company TransCanada that the $7 billion proposal will create 20,000 jobs, mostly from construction, over two years and provide a reliable source of oil. But environmentalists and a growing number of Nebraskans are resisting.

The pipeline would be laid directly through the aquifer at the depth of at least four feet and deeper in many places, raising fears of catastrophic damage if any part of the tube were to rupture. It would carry 700,000 barrels of oil a day.

Nebraska Gov. Dave Heineman (R) and other officials have urged TransCanada to pick a different route that skirts the aquifer, but Heineman doubts the company will take his advice.

TransCanada officials have insisted the pipeline is safe and has undergone a vigorous federal review.

“If the activists feel that they’re facing an uphill battle, it’s because the facts don’t support their overheated rhetoric,” TransCanada spokesman Shawn Howard said. “It has been shown that the outrageous claims these groups have made aren’t true. They can repeat it over and over and over again, but that doesn’t change that fact.”

Other government agencies have reported no major problems with the plan.

An environmental review by the State Department found that neither the construction nor operation of the pipeline was likely to cause serious environmental problems. And Energy Secretary Steven Chu spoke favorably of the project this month, noting the advantages of buying oil from a close ally and arguing that new technology makes such operations safer.

Five major alternative routes considered to avoid the aquifer were found to have a “worse or similar” environmental impact, Jones said.

University of Nebraska hydrologist Jim Goeke, a retired professor who has studied the pipeline proposal for years, believes it’s safe. He says the aquifer is composed of layers of loose sand, sandstone, soot and gravel that would impede the spread of an oil leak.

Goeke, who has no formal role in the project, said he expects pipeline opponents to make an impassioned case that the aquifer would be endangered, but he doesn’t buy it.

“I’d be comfortable if the pipeline was defeated on the basis of good, sound science and not emotion,” Goeke said. “I think it’s a reflection of the pride and love Nebraskans have for the Ogallala Aquifer. A lot of people love and treasure the aquifer, and they’re concerned the entire aquifer is at risk. And that just isn’t factual.”

Besides the risk to the aquifer, environmental groups fear the pipeline could foul surface water, threaten wildlife habitats and increase air pollution around refineries. They have criticized what they consider inadequate pipeline safety and emergency spill responses.

Anthony Swift, a policy analyst at the Washington-based Natural Resources Defense Council, said the State Department’s decision to schedule more hearings showed that federal officials were feeling increased pressure from opponents.

A high-profile anti-pipeline campaign included repeated arrests of activists outside the White House.

“This is not simply an issue being made at an agency level anymore,” Swift said. “It’s a decision being made by the Obama administration.”

State Department spokesman Noel Clay said the public comment period will close Oct. 9, two days after the last public meeting, which will be held in Washington.

Secretary of State Hillary Rodham Clinton will make the pipeline decision personally, unless another federal agency objects, which would send the choice to President Obama.

— Associated Press