Washington (CNN) -- Thousands of protesters held hands and encircled the White House grounds on Sunday, demanding President Barack Obama reject a proposed oil pipeline that would stretch between Canada and Texas.
"Stop the pipeline, yes we can!" the environmental activists chanted about the 1,700-mile Keystone XL project.
Until last week, the White House had said final decision on the pipeline would be up to the State Department, following an environmental impact analysis and a public commenting period. But Obama has implied recently that he may step in.
Those gathered Sunday afternoon in Washington -- from as far north as Maine, as far south as Florida and as far west as Nebraska, said organizers -- hoped public pressure would persuade the president.
"We need to remind him he is the leader who we elected," Courtney Hight, a former member of the White House Council on Environmental Quality and now executive director of the Energy Action Coalition, told the crowd. "(We need him) to give back some of the hope he gave us three years ago."
She was among several who began speaking around 2 p.m., in addition to U.S. Rep. Steve Cohen, D-Tennessee, actor Mark Ruffalo, Jim Wallis of the progressive Christian group Sojourners and scientist James Hansen.
Many people in the crowd wore orange vests that read, "Stop the pipeline," while a few dressed as polar bears. A large model of a black pipeline was held aloft and walked around the White House several times.
"I'm hoping to God that the president, or whatever higher power, will use rational sense and understand that people don't want this," Willa Tharnish, a senior and environmental studies major at the University of Nebraska at Lincoln, said of the project.
Pipeline operator TransCanada says on its website that the $13 billion pipeline "will play an important role in linking a secure and growing supply of Canadian crude oil with the largest refining markets in the United States, significantly improving North American security supply."
TransCanada says it "is devoted to minimizing its environmental impact" in creating and operating Keystone XL.
"In all cases, great care and planning will be taken to minimize and avoid impacts to the environment, including rare or endangered species, habitat, significant water crossings, and historical and paleontological resources," the company says.
While saying it is ready to respond to any leak or crisis, TransCanada stresses that it believes pipelines "are safe and the chance of a significant spill is remote."
"Pipelines are the safest, most reliable, economical and environmentally favorable way to transport oil and petroleum products," says the company.
Yet environmental activists have decried the project, with the Energy Action Coalition calling it "potentially catastrophic."
The pipeline would transport toxic crude oil from under Canada's Boreal forest, home to many North American songbirds, to refineries in Texas, according to the Natural Resources Defense Council. The process threatens rivers and communities along the way, said the group, which was one of the chief organizers of Sunday's event.
Environmentalists additionally are urging the president to block construction in the spirit of his 2008 campaign promise to move the country away from fossil fuels.
Hight told CNN that she felt a State Department review of the project is flawed, adding that she feels Obama needs to stand up to "big oil."
Michael Brune, the Sierra Club's executive director, said from the rally that he felt the activist push against the pipeline is surging. He added that he fully expects Obama to reject the project. Hight said that the arrests of hundreds of activists over the summer "brought the issue into the radar."
While he hasn't made a decision, the president chimed in about the project in an interview last week with CNN affiliate KETV in Omaha, Nebraska.
"Folks in Nebraska, like folks all across the country, aren't going to say to themselves, 'We're going to take a few thousand jobs if it means our kids are potentially drinking water that would damage their health,'" Obama said. "When somebody gets sick, that's a cost that society has to bear as well. So these are all things that you have to take a look at when you make these decisions."
The president said his priority is to ensure residents are not at risk.
"There's a way of doing that and making sure the health and safety of the people of Nebraska are protected," he said. "And that's how I'll be measuring these recommendations when they come to me."