US President Barack Obama might back off his threat to veto legislation approving the controversial Keystone XL pipeline to carry oil from Canada to the Gulf, a Democratic lawmaker said Friday.

Representative Emanuel Cleaver told MSNBC television that Obama might bow to House Republicans who have attached the pipeline measure to legislation to extend a tax cut that benefits middle-class voters as well as jobless aid.

"The president is serious. But in politics, I think everybody understands that you get the best deal you can," said Cleaver, who chairs the Congressional Black Caucus.

Obama has pushed lawmakers to approve the payroll tax cut extension as well as prolong unemployment benefits but threatened to veto the legislation if it sought to override his decision to delay the pipeline.

Supporters say the plan to bring oil from Canada's tar sands to the United States is the ultimate shovel-ready job creation project and would spur the hiring of thousands of workers.

Environmental activists fear an accident along the 1,700-mile (2,700-kilometer) pipeline extension would be disastrous for aquifers in central US Great Plains states.

Others oppose the multi-billion-dollar project because exploiting the tar sands requires energy that generates a large volume of greenhouse gases that scientists blame for global warming.

The Obama administration has ordered an extra environmental assessment of a possible new route through Nebraska, which could delay a final decision until after next November's election.

That move prompted Obama's opponents to accuse him of dodging a difficult issue to avoid angering sections of his Democratic political base vote.

Asked about the veto threat, Cleaver acknowledged that "at the end it may be that 'here's an opportunity to get a deal and get what I want and we go home.'"

The lawmaker said the Republicans had settled on the pipeline issue out of "desperation" and a need to be able to say "they were the winners" in this latest standoff with the White House.

"I think the president probably feels that throwing in the pipeline is not a good deal. I think the president is a good-government president, but I think whether or not he will delay the deal is another issue.

Cleaver said it would be "unfair" to advance the pipeline this way, but added: "I do think that if I had one minute to vote, I'd probably vote to accept the deal, but it's not good government."

"The public wants us to pass the UI (jobless benefits) as well as the payroll tax," he said. "But this will be a dumb decision."