Lugsoul - Is it your understanding the Mayor and Governor have not instituted Martial Law and thus our military cannot come help law enforcement in New Orleans?
Even with regard to active duty military, I think they can do everything except actual law enforcement. And could probably even do force protection while they were involved in other activities - whether they be logistical, SAR, or whatever.
The problem with martial law - and there are problems with it - is that this then becomes a Federal problem, all the way around. I don't think they could workably delegate LE to the US military while retaining other functions on a state or local level. I don't think LA or NO want that, and I don't think Washington wants that.