Speaking as NATO defense minister met in Brussels, Rasmussen downplayed suggestions a gradual transition starting in mid-2013 meant the alliance was ending its combat role in Afghanistan early.
All NATO-led foreign troops are scheduled to leave Afghanistan by the end of 2014.
"We expect the last provinces to be handed over to the Afghanistan security forces by mid-2013. From that time, Afghan security forces are in the lead all over Afghanistan," Rasmussen said. "And from that time, the role of our troops will gradually change from combat to support. In that, there's nothing new."
Earlier, U.S. Defense Secretary Leon Panetta said American and other foreign troops in Afghanistan hope to end their combat mission as soon as mid-2013 and begin the transition to a "training, advise-and-assist role."
French President Nicolas Sarkozy told Afghan President Hamid Karzai this week that France wants to end its combat mission in Afghanistan in 2013.
French officials have said some French troops would provide training to Afghan forces after 2013, comments that appeared to echo Panetta's outline.
Panetta said he wants to hear more from the French defense minister during his talks on February 2-3 in Brussels, allowing him to clarify whether there are any serious differences between the French stance and NATO's timeline for a complete withdrawal by the end of 2014.
Panetta also insisted that a 2013 end to combat operations was in line with a previous NATO strategy agreed in Lisbon, Portugal.
Afghan officials say an early withdrawal would rush the transition and leave Afghan forces unprepared to provide security in the country.
Panetta described the role of U.S. forces in Afghanistan during 2014 as being "pretty robust," adding that the change to an advisory and training role "doesn't mean that we're not going to be combat-ready."
"The Washington Post" has cited an unnamed U.S. official as saying "nothing is final" and that decisions about the pace of withdrawal would not be made until a NATO summit in Chicago in May.
The U.S. announcement of a security transition starting in 2013 comes ahead of the U.S. elections in November, giving incumbent President Barack Obama an opportunity to say during campaigning that American troops have left Iraq and would soon be out of Afghanistan.
Compiled from agency reports