WASHINGTON, Dec 19 (Reuters) - U.S. President Barack Obama said on Friday that construction of the Keystone XL pipeline to transport crude oil from Canada to the U.S. Gulf Coast would only nominally benefit American consumers and workers in perhaps his strongest comments on the Canada-to-U.S. pipeline to date.

"There is very little impact - nominal impact - on U.S. gas prices, what the average American consumer cares about," Obama told reporters during an end-of-year press conference.

Obama picked apart some of the most common arguments of its proponents: that it would create jobs, lower domestic gasoline prices and bolster the U.S. economy.

"There has been this tendency to really hype this thing as some magic formula to what ails the U.S. economy," Obama said.

His comments come as Republican leader Mitch McConnell has said his party's first act in the new Republican-controlled Senate would be to pass a bill fast-tracking approval of the $8 billion project, which would transport more than 800,000 barrels of oil a day from Alberta to Nebraska en route to the Gulf of Mexico.

Obama had been widely expected to veto a failed November attempt in the Senate to approve the pipeline.

Construction workers, unions and energy companies vocally support the pipeline. Environmentalists say developing Canada's oil sands would spike carbon emissions and that much of the oil or refined products would be sold abroad.

But Obama said there are better ways to spur job growth.

"When you consider what we could be doing rebuilding our roads and bridges around the country, something the Congress could authorize, we could probably create hundreds of thousands of jobs - or even a million jobs," he said.

While Obama did not outright reject Keystone, his comments marked the third time in four weeks that the president has publicly questioned whether it is in the national interest.

"It's good for the Canadian oil industry, but its not going to be a huge benefit to us consumers," he said.

Pipeline advocates said Obama does not acknowledge the role Canadian oil plays in the United States.

"The president doesn't seem to understand that oil from Canada is helping provide relief at the pump - right now," said Matt Dempsey with pro-pipeline group Oil Sands Fact Check.

Canadian Foreign Minister John Baird said Ottawa would continue to work with Washington to press for approval.

"We're going to continue as a government to promote our interest," he said. (Reporting by Valerie Volcovici and Amanda Becker; additional reporting by Randall Palmer in Ottawa)