What will that entail? “A lot of it will be trying to deal with the al-Qaeda presence, particularly in Ninewa Province,” said Joseph McMillan, the principal deputy assistant secretary of defense for international security affairs, on a bloggers’ conference call this morning. McMillan declined to get more specific, but said to expect “the tracking of insurgent activities, particularly on the borders” as a hallmark of U.S. troops’ new wilderness-focused combat mission.

Under what circumstances can U.S. forces operate in the cities after Wednesday? That’s “essentially a call by the Iraqi government,” McMillan continued. “If they tell us they need help, then Gen. Odierno and his staff will sit down with the Iraqi military and security leadership [to determine] what missions are appropriate,” and how to execute them in a supporting role. He added that even though about 120 bases operated by U.S. forces in urban areas have been handed over to Iraqi leadership, there hasn’t been much base construction for facilities out in the sticks. “My understanding is they’re doing minor work, the standard engineering thing” to accommodate an increased volume of U.S. forces in the facilities, but “we’re not in the mode of building new bases around the countryside.”

McMillan rejected the idea that the pullout from Iraqi cities represented a return to a pre-surge combat posture, when U.S. troops were criticized for “commuting to the fight” from big bases on the outskirts of Iraqi cities. From 2003 to now, “U.S. forces operated with the freedom to go into anywhere” deemed appropriate by their commanders, he said, and didn’t provide the responsibility for urban security to their Iraqi counterparts. “This is a fundamental change of the rules of the road. We are now handing off the urban security mission to Iraqi security forces.”