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.

Secretary of State John Kerry asked eight other agencies to weigh in on the project. The deadline for those responses was Monday, and the State Department has not publicly released comments from all of the agencies.

The letter notes that the State Department’s environmental review concluded that the process of extracting oil from the Canadian oil sands produces about 17 percent more greenhouse gas pollution than the process used to extract conventional oil — but that the oil was likely to be produced, extracted and brought to market with or without construction of the pipeline.

It concluded that without construction of the pipeline, the oil would be brought to market by rail.

However, that review also found that demand for the oil sands fuel would drop if oil prices fell below $65 a barrel, since moving oil by rail is more expensive than using a pipeline. The price of oil closed at $51.87 a barrel at midafternoon Tuesday.

Ms. Giles noted that over the long term, the price of oil would probably rise. But, she wrote, “given the recent large declines in oil prices and the uncertainty of oil price projections, the additional low price scenario included in the Final S.E.I.S. should be given additional weight during decision making, due to the potential implications of lower oil prices on project impacts, especially greenhouse gas emissions.” Final S.E.I.S. is the State Department’s final supplemental environmental impact statement.

It is a small distinction, but one that shows the E.P.A. emphasizing quietly that, in some outcomes, the pipeline could contribute to additional greenhouse gas emissions.

Meanwhile, pressure is rising on Mr. Obama to make a decision, which he has been waiting to do since the start of his administration. Next week, the House is expected to pass a bill that tries to force his approval of the pipeline. Mr. Obama is expected to veto that measure, although that would not necessarily signal that he would oppose the pipeline itself.

While it had long been expected that Mr. Obama would approve the pipeline — an infrastructure project that would bring oil to the United States from Canada, a strong ally — he has recently made critical comments about the project. Some analysts have speculated that he may wish to deny the project as a way to make a symbolic statement about his broader commitment to climate change issues.

“By focusing on the emissions related to an energy resource that is developed outside of the United States, the E.P.A. is ignoring the fundamental sovereignty of another country and the significant steps that Canada and Alberta have already taken to reduce emissions,” the TransCanada Corporation, the company that wants to build the pipeline, said in a statement.

“Respectfully, this goes far beyond the mandate of the E.P.A., and legislators and others would not appreciate other countries interfering in issues of American federal or state sovereignty,” the statement said.