NEW ORLEANS — With much of the city flooded by Hurricane Katrina, looters floated garbage cans filled with clothing and jewelry down the street in a dash to grab what they could. In some cases, looting on Tuesday took place in full view of police and National Guard troops. At a Walgreen’s drug store in the French Quarter, people were running out with grocery baskets and coolers full of soft drinks, chips and diapers. When police finally showed up, a young boy stood in the door screaming, “86! 86!” — the radio code for police — and the crowd scattered.