President Barack Obama and British Prime Minister David Cameron have firmed up their intention to move military forces to a support role in Afghanistan by 2013.
The final details are likely to be made public at a Nato meeting in May, but Mr Obama says there will be no sudden changes in policy relating to current events.
The mission in Afghanistan is moving into its "final phases", David Cameron said, at a joint press conference with the US president.
Speaking at the White House, both leaders stressed that progress had been made in the country - despite losses of US, British and Afghan lives.
International forces will take on a support role from 2013, and Afghans will fully take over security in 2014.
Mr Cameron said they would not "give up on this mission", despite its "high cost".
Tensions are high in Afghanistan after an American soldier shot dead 16 Afghan civilians
Mr Cameron is currently in the United States for bilateral talks between the two countries.