The reduction is about a one-third drop from the current number and would be the first big withdrawal this year.
Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, disclosed the troop numbers but provided no details. He declined to elaborate on the ongoing negotiation between Iraq and the U.S. over leaving a small force there after year's end.
Mullen spoke at the Carnegie Endowment for International Peace.
There are about 44,500 U.S. troops in Iraq. When the U.S. officially ended its combat mission in Iraq on Sept. 1, 2010, it had about 50,000 troops. Under a 2008 agreement, all U.S. troops are to be out of Iraq by the end of this year.
"This is the drawdown plan that Gen. Austin's had in place specifically, and it's really a plan that gets us to, under the current agreement, to (pulling) all the troops out by the end of December," Mullen said later during a news conference with Defense Secretary Leon Panetta. Gen. Lloyd Austin is the top U.S. commander in Iraq.
Talks are under way with Iraq to consider leaving at least a few thousand U.S. troops in the country to help train Iraqi forces. Mullen said it is a difficult process, and there still have been no final decisions on troop levels beyond Dec. 31.
Asked about plans for the U.S. Embassy to hire 8,000 private security contractors to protect American personnel and buildings in Iraq if the military leaves, Panetta said that the issue is part of the negotiations.
"One of the concerns we always have is the importance of providing adequate security, and I think that will be one of the issues that will be involved in these negotiations," he said.
AP National Security Writer Robert Burns contributed to this report.