President Barack Obama will attend the United Nations climate change summit in Copenhagen where he will offer cuts in US greenhouse gas emissions.
The White House has said the president will announce a plan to cut emissions in the United States in several stages, beginning with a 17% cut by 2020.
Mr Obama will attend the summit for one day, on 9 December. UN climate chief Yvo de Boer said his attendance could be vital for a deal.
So far more than 60 world leaders have said they will attend the talks, aimed at drawing up a new global climate treaty to supplant the 1997 Kyoto Protocol.
The BBC reports that the presence of such figures as Mr Obama will raise hopes for action on climate change, although the talks are not expected to result in a new treaty.
US pledge
Officials said the US would pledge a 17% cut in emissions from 2005 levels by 2020, 30% by 2025, 42% by 2030 and 83% by 2050.
Most other countries' targets are given in comparison with 1990 figures.
A BBC correspondent says that on that basis, the US figure amounts to just a few percentage points, as its emissions have risen by about 15% since 1990.
This is much less than the EU's pledge of a 20% cut over the same period, or a 30% cut if there is a global deal; and much less than the 25-40% figure that developing countries are demanding.
