I think once you reach the point of actual riots in the streets, you've pretty much lost, and there isn't a good answer at that point. The correct answer is to not get into the situation in the first place. I've spoken at some length about this with Norm Stamper, a neighbor of mine who was the Police Chief of Seattle during the WTO riots there. He wrote a nice article about the topic a couple years ago:
http://www.thenation.com/article/164...py-wall-street
As to local police forces with riot gear and armored vehicles, handy for very small events or assaults on strongholds of Very Bad People, but for widespread chaos, I bet you these guys do not train and plan enough to be successful in these larger events (as is shown in their performance in the field). I think this video is a must-watch: