The transition from NATO to Afghan forces will begin in July.
It's the first step in Karzai's plan to have Afghan police and soldiers protecting the entire nation by the end of 2014.
The tenuous step comes despite NATO predictions of bloody fighting this spring and Afghans' fears that their forces aren't up to the task.
NATO forces that are currently in transition areas will thin out, take on support roles, including training and mentoring, be redeployed to other areas of the country or sent home.
President Barack Obama wants to start withdrawing U.S. troops in July if conditions allow.
The Associated Press contributed to this report.