WASHINGTON — An Environmental Protection Agency review of the Keystone XL pipeline emphasized that the recent drop in global oil prices might mean that construction of the pipeline could spur increased development of the Canadian oil sands — and thus increase planet-warming greenhouse gas emissions.

That review might influence President Obama’s long-delayed verdict on the 1,179-mile pipeline, which could bring about 800,000 barrels of oil per day from Alberta to the Gulf Coast. Mr. Obama has said that an important element of his decision will be whether construction of the pipeline would contribute significantly to climate change.

“I think that in their careful way, they are pointing out that this does fail the president’s climate change test,” Tiernan Sittenfeld, a senior vice president at the League of Conservation Voters, said of the E.P.A. review. “We think these comments are a big deal, and they make us more confident that the president is going to reject this dangerous pipeline.”

The letter, which came from Cynthia Giles, the assistant administrator of the E.P.A., and was posted on the E.P.A. website on Tuesday, came in response to an 11-volume environmental impact statement on the project that was produced last year by the State Department.