He will arrive later than initially planned, moving his appearance from 9 December to 18 December.

The White House said he believed "that continued US leadership can be most productive through his participation at the end of the Copenhagen conference".

The summit aims to draw up a treaty to succeed the 1997 Kyoto Protocol.

The president had changed his plans after talks with other leaders and after seeing "the progress that has already been made to give momentum to negotiations".

US representatives will attend the Copenhagen summit throughout the negotiations, the White House said.

The president believed recent progress included the emissions reduction target announced by the US; China and India setting targets for the first time to reduce their carbon intensity and moves by members of the Commonwealth.

The White House said the president had discussed the state of the negotiations with Australian Prime Minister Kevin Rudd, German Chancellor Angela Merkel, French President Nicolas Sarkozy and British Prime Minister Gordon Brown.

He concluded there appeared to be growing support for the suggested $10bn annual fund to help developing countries deal with climate change.