Obama is expected to withdraw roughly 10,000 U.S. troops from Afghanistan this year, with one brigade of about 5,000 forces leaving this summer and a second brigade of similar size coming home by the end of the year, a senior U.S. defense official said Tuesday.
Obama is hoping to pave the way for Afghans to control their own security by 2014.
The Pentagon wants to keep as much combat power in Afghanistan for as long as possible to keep pressure on the Taliban.
The White House said Obama will speak at 5 p.m. PST.
The Associated Press contributed to this report.