TALLINN, Estonia — NATO agreed today to begin handing over control of Afghanistan to the Afghan government this year, a process that if successful would enable President Barack Obama to meet his target date of July 2011 for starting to bring U.S. troops home.

NATO Secretary General Anders Fogh Rasmussen said the 28-nation alliance is on track with its new strategy for winding down the war in Afghanistan, despite security setbacks and a continuing shortage of foreign trainers for the fledgling Afghan police and army.

He said a meeting of NATO foreign ministers, including U.S. Secretary of State Hillary Rodham Clinton, agreed on what it will take to create conditions enabling Afghans to assume control of their own country. He was not specific about what those conditions will be, but said progress in that direction is important to avoid further erosion of public support for the war effort.

"Where it occurs, the transition must be not just sustainable but irreversible," Fogh Rasmussen told a news conference at the conclusion of the two-day meeting.

In earlier remarks, Fogh Rasmussen offered a mostly upbeat assessment to the gathering.

"Increasingly this year the momentum will be ours," he said.

Fogh Rasmussen asserted that the Afghan government, which has been hampered by a Taliban insurgency, political corruption, a dysfunctional economy and a dependence on foreign assistance, is starting to take more responsibility for running the country's affairs.

"We are preparing to begin the process of handing over leadership, where conditions allow, back to the Afghan people," he said.

"The future of this mission is clear and visible: more Afghan capability and more Afghan leadership."