Lights on a tree are powered by people cycling and generating electricity that form part of exhibit for the climate change conference happening in Durban, South Africa. (Schalk van Zuydam/AP)

The letter, signed by 16 different organizations, says that while President Obama pledged in November 2008 to “engage vigorously in these negotiations, and help lead the world toward a new era of global cooperation on climate change,” he has failed to deliver on that vow. The letter is to be released Wednesday, in an unusual public rebuke. The Washington Post obtained it Tuesday.

“Three years later, America risks being viewed not as a global leader on climate change, but as a major obstacle to progress,” they wrote. “U.S. positions on two major issues – the mandate for future negotiations and climate finance – threaten to impede in Durban the global cooperation so desperately needed to address the threat of climate change.”

While the European Union and environmental groups are pressing for a commitment to engage in talks that could lead to a legally-binding climate treaty in 2020, U.S. special climate envoy Todd D. Stern has said it would be premature to commit to that discussion when it is unclear what the pact would look like. The U.S. has also raised concerns about several details related to the Green Climate Fund, which aims to mobilize $100 billion by the end of the decade to help poor countries cope with global warming and reduce their greenhouse gas emissions.

In a press conference with reporters earlier this month, Stern said the administration was wary of signing up for a binding agreement that would not pass muster with Congress.

“You ought to know what the content is before you make a final decision on form,” he said, adding “We’re trying to approach an international negotiation in a way that has the hope of attracting congressional support.”

One of the lawmakers most opposed to curbing greenhouse gas emissions, Sen. James M. Inhofe (R-Okla.), said in a statement Tuesday: “The far left should feel betrayed by President Obama. Despite overwhelming Democratic majorities in Congress when he came into office, he failed to deliver on his promise to bring the United States into the Kyoto process. And his abandonment of the international process now means that he should put an immediate halt on all domestic global warming regulations.”

The U.S. has called for major emerging economies such as China and India--which now rank as the world’s first- and third-biggest emitters of greenhouse gases—to commit themselves to greater international scrutiny and to binding obligations to cut their own carbon emissions.

The environmental CEOs, including leaders of the Sierra Club, Natural Resources Defense Council and the Union of Concerned Scientists, wrote that these demands are unrealistic.

“It will clearly not be possible to reach consensus on these issues in Durban; insisting on their inclusion in a mandate sends the signal that the U.S. does not support such a mandate. This is a lost opportunity,” they wrote. “The U.S. should be working with the EU, China and others to make this type of a mandate possible, not rejecting it out of hand because it doesn’t guarantee all of the U.S. negotiating objectives.”

The activists also criticized the U.S. for not allowing negotiators to discuss how they might impose global fees and taxes to raise money for the Green Climate Fund.

The State Department did not respond to a request for comment on the letter.

Jennifer Haverkamp, who directs the international climate program at the advocacy group Environmental Defense Fund, said the administration is in no position to make such stringent demands overseas when it has failed to impose nationwide limits on greenhouse gas emissions at home. She noted that one of the reasons there has been “slow progress on the international front is because of the empty pockets the U.S. brings to the table… It would be extremely unfortunate if the U.S. domestic situation had the U.S. hold others, who are willing to start a negotiation, hostage to a U.S. domestic situation.”