While accepting that the "US clearly has to do its part", the official said no meaningful treaty can come unless major developing nations such as China and India also produced meaningful submissions.
However, Yvo de Boer, the UN climate chief, said that the participation of Obama was vital to achieving something at the talks.
"My sense is Obama will be in a position to come to Copenhagen with a target and a financial contribution," he said on Monday.
De Boer has already ruled out the possibility that a comprehensive treaty can be reached in Copenhagen, but said that he believed "a very specific agreement" could be found.
He said that the lesser deal he anticipated was likely to include "a list of rich country targets [and] clarity on what major developing countries like India and China are willing to do".
Norbert Roettgen, Germany's environment minister, said at talks in Brussels on Monday that no-one could expect a "legally constraining" deal in Copenhagen, but that "obstacles must fall" as a result of the summit.
Jean-Louis Borloo, the French ecology minister, said the Washington "problem" would mean "a flexibility on dates or figures.US legislation
Last week, Harry Reid, the US Democratic Senate majority leader, said that the senate would not enact new legislation on climate change until next spring.
However, hopes that the world's biggest emitter of greenhouse gases will move to reduce its impact have grown due to positive moves from the White House.
On a trip to Beijing two weeks ago, Obama stressed, along with his Chinese counterpart, the importance of co-operating to come up with a workable deal to tackle climate change and cut emissions.
China is also one of the largest emitters of greenhouse gases.
Obama said during the visit: "This kind of comprehensive agreement would be an important step forward in our effort to rally the world around a solution to our climate challenge."
As evidence of the US and China's ambitions to reduce emissions, Obama pointed to a recent agreement between the two major emitters to create a joint clean energy research centre.