WASHINGTON - U.S. President Barack Obama wasn't around to see it, but 65 protesters were arrested Saturday as they participated in a peaceful protest outside the White House aimed at pressuring him to block TransCanada's controversial Keystone XL pipeline.

Bill McKibben, a leading American environmentalist and one of the organizers of the two-week protest, was among those arrested. Others included gay rights activist Dan Choi; Jane Hamsher, the founder of the popular liberal blog Firedoglake; and Gus Speth, a onetime environmental expert under former president Jimmy Carter.

About 100 protesters, carrying a large banner that read "Climate Change Is Not In Our National Interest," gathered at Lafayette Square directly north of the White House on a sunny and humid Saturday morning. They chanted "hey-ho, Keystone XL has got to go" as they stood on the sidewalk that runs along the White House's wrought-iron fence.

When they didn't respond to requests to move from the sidewalk, U.S. Park Police and SWAT officers handcuffed them and removed them from the area one after the other.

Obama, meantime, was vacationing with his family in Martha's Vineyard.

But when he returns late next week, the protesters say they'll still be there to protest a Canadian project that has become a lightning rod for the U.S. environmental movement in the wake of failed climate change legislation once passionately promoted by Obama.

"It's not the easiest thing on Earth for law-abiding folk to come to risk arrest," McKibben said before his arrest.

"But this pipeline has emerged as the single clear test of the president's willingness to fight for the environment. So I wore my Obama '08 button, and I carry a great deal of hope in my heart that we will see that old Obama emerge."

As many as 2,000 people are expected to participate in the civil disobedience that began Saturday and will continue until Sept. 3 with daily gatherings outside the White House.

They're staging the protest as the U.S. State Department is poised to release its final environmental assessment of TransCanada's US$7 billion project. That report is expected within days, and Obama will then have 90 days to decide whether granting the Calgary-based oil giant a pipeline permit is in the U.S. national interest.

Keystone XL will carry millions of barrels of oilsands crude a week from northern Alberta through the American heartland to Gulf Coast refineries.

Some celebrities are endorsing the protest, including actors Mark Ruffalo, Danny Glover and Canadian Margot Kidder, who now lives in Montana as a U.S. citizen.

Environmentalists say the Keystone XL has the potential to wreak havoc on America's agricultural heartland and point to recent large-scale pipeline oil spills. Proponents of the pipeline, including most congressional Republicans, consider the project a major job creator that will help end American reliance on Middle East oil.

The U.S. State Department is tasked with making a decision on the pipeline because it crosses an international border. In recent talks in Washington between Hillary Clinton and Foreign Affairs Minister John Baird, the secretary of state was exceedingly cautious when discussing the pipeline, says a source familiar with the discussion.

The International Brotherhood of Teamsters, one of the largest and most influential unions in the U.S., backs the project, saying it will create 1,500 jobs for its members. But on Friday two other major unions -- the Transport Workers Union and the Amalgamated Transit Union -- said they're opposed because of environmental concerns.