There are a number of problems with such proposals, however.

First, pipeline opponents say there is no possible deal that could compensate for the environmental damage created by the construction of the pipeline and expanded development of the Canadian oil sands. They have described the pipeline as a fuse to one of the biggest carbon bombs on the planet, and said that extracting and burning all the oil in the Alberta oil sands would mean the game was over for global climate.

“Approving the pipeline would be a deep self-inflicted wound on the Obama administration, greater than anything else he has done,” said Michael Brune, executive director of the Sierra Club and a leader of the antipipeline movement. “This was not inherited from the Bush administration and it can’t be passed off to his successor. It really is Obama’s alone. Whatever damage the decision would do to the environmental movement pales in comparison to the damage it would do to his own legacy.”

Mr. Brune and other environmental advocates say that Mr. Obama should veto the pipeline and pursue climate-friendly policies for their own sakes, not as part of some political deal. The danger to the climate of continuing on the current path demands strong steps like curbing coal-fired power and supporting renewable alternatives, he said.

“It’s hard to argue we should be developing new fossil fuel sources,” said Mr. Brune, who was arrested outside the White House at a Keystone protest earlier this year, “but particularly such a carbon-intensive source as the Canadian tar sands.”

There are other difficulties. Last year the Environmental Protection Agency proposed limiting carbon dioxide emissions from new power plants, effectively foreclosing construction of any new coal-burning facilities. But just last month the E.P.A. delayed the proposed rule, saying it needed to respond to public and industry concerns.

It is unlikely the administration will take on the far more contentious and costly project of curbing greenhouse gas emissions from existing power plants until the new plant rule is completed, or at least much further along than it is now. This week, Gina McCarthy, who is awaiting confirmation as the new E.P.A. administrator, told Senate Republicans in a written submission that the agency “is not currently developing any existing-source G.H.G. regulations.” G.H.G. is shorthand for greenhouse gas.

A clean energy standard, also known as a renewable portfolio standard, also presents problems. About 30 states already have such rules in place, with different targets and timelines. To impose such a regimen nationally, however, requires Congressional action, which is unlikely. A clean energy proposal last year from former Senator Jeff Bingaman, Democrat of New Mexico, went nowhere and there is even less enthusiasm in the current Congress.