Manning, who was arrested last year, faces more than two dozen charges related to his alleged leaking of materials that were published by Wikileaks. The leaks include video of a helicopter attack in Iraq where two Reuters journalists were killed and classified State Department cables.
The most serious charge against Manning is a capital offense, but prosecutors have said they will not seek the death penalty.
Coombs said that the December hearing would last for about five days. The hearing will be open to the public, except when classified material is being discussed.