It would be stupid and unnecessarily expensive to relocate soldiers on duty in Afghanistan and Iraq to help with Katrina relief efforts (given current needs and availability of aid).
Why? Because there are still plenty troops available still in the Country. Approximately 38,200 Army, Navy, and National Guard personnel have already been sent into the effected areas. Why bring soldiers from Afghanistan and Iraq when they can get them from Louisiana, Mississippi, and Wisconsin (to name a few)? About one third of the troops are going to be allocated to help in law enforcement efforts such as help enforce curfew and quell the looting.
http://www.ngb.army.mil/
Further, military personnel are not the only folks aiding in the relief effort. Further personnel will come from other jurisdictions under "mutual aid", State and Federal disaster relief organizations, organizations like the Red Cross, and a heavy dose of disaster relief volunteers.
As I mentioned in a previous post, it takes time for the government to get things going in a disaster relief effort. The end result is that the effected areas will get whatever help they need from the Government and from private sector companies and individuals.
The Federal and State governments are actually doing pretty good so far. They were able to move in some personnel and equipment to outlying areas before the hurricane hit. Remember, this is the aftermath of a historically significant hurricane. It will take 1 - 2 years to undo the damage to the city structures. You can't reasonably expect overnight miracles.
Reading the text with an open mind also helps, bold emphasis added:
This means there
could be
some shifting of troops if this becomes necessary.