GALESBURG, Ill. — President Obama said in an interview that he would evaluate construction of the Keystone XL pipeline on the basis of whether it would significantly contribute carbon to the atmosphere.

But he mocked Republicans’ arguments that the approval of the pipeline, which would carry oil from Canada to the Gulf Coast, would create many jobs in the United States.

“Republicans have said that this would be a big jobs generator,” Mr. Obama said in an interview with The New York Times. “There is no evidence that that’s true. The most realistic estimates are this might create maybe 2,000 jobs during the construction of the pipeline, which might take a year or two, and then after that we’re talking about somewhere between 50 and 100 jobs in an economy of 150 million working people.”

He said 2,000 jobs were “a blip relative to the need.”

The president also disputed the argument that the pipeline would help lower retail gasoline prices. He said most of the oil would be destined for refineries on the Gulf Coast and then exported. In fact, he said, the pipeline might increase prices somewhat in the Midwest, which would suddenly be able to ship more of its oil to other parts of the world.