Deputy Police Chief Warren Riley said thousands of people were still in the city a week after Hurricane Katrina ripped across southeast Louisiana.
"We are working with them to try to convince them that there is no reason -- no jobs, no food -- no reason for them to stay," Riley said.
"We advise people that this city has been destroyed. It has been completely destroyed."
Riley said law enforcement wasn't involved "in taking people off the street and forcing them out of the city at this point. There may come a time when we do that."
Most of the streets are filled with stagnant, fetid waters streaked with iridescent oil and smelling of garbage, human waste and death.
"There's just a lot of water in eastern New Orleans, more water than we're capable of dealing with," Orleans Parish Sheriff Paul Valteau said, calling the influx of troops and National Guard a godsend.
Outside New Orleans, in the suburban parishes of Jefferson, Plaquemines, St. Bernard and St. Tammany, floodwaters remained high.
In a handful of areas, pumping stations were at last up and pushing water out of the streets -- although normally dry flood basins, such as those near Chalmette and Arabi, were still near capacity.
Jefferson Parish, on the west and dry side of the 17th Street Canal from a levee break that flooded downtown New Orleans, allowed residents to return Monday for the day only to assess damage to their homes.
They had to be out by dusk, and they discovered not all the parish escaped the floods.
Mortuary teams from the Federal Emergency Management Agency moved out to locate the dead, but the police's main focus remained on rescue operations, Riley said.
Despite the horrid conditions, he said he could see improvements.
"We moved from chaos to organized chaos," Riley said. "There was a period of time when we could not communicate with each other, when we had officers stranded all over the city. Those things have changed."
He said law enforcement had gotten a better grip on the city and was focusing its efforts on "looters and people who want to create mayhem."
Police killed two people Sunday on the Danziger Bridge over the Industrial Canal, he said.
The incident began when a rescue worker heard gunshots and called police. When the responding unit saw six people on the bridge with guns, they called in a task force unit, which confronted the group, according to Riley.
"The subjects fired on the task force, which returned fire," he said, killing two on the scene and wounding two others. The other two fled and the task force pursued, wounding one and capturing the other.
All three of the wounded were hospitalized, Riley said.
Riley expressed concerned about the mental health of his officers, saying they "have been through hell."
"All of our officers are not accounted for," he said, noting that about 400 to 500 of 1,600-member force were missing and more just aren't on duty.
"Some we understand -- they're searching for family; they lost their homes," he said. "Some left because they simply could not deal with this catastrophe."
New York City sent another 150 police officers to Louisiana to aid in the relief effort Monday, said Police Commissioner Raymond Kelly said. They will join 172 officers who left Saturday.
Of the more than 2,000 police officers who volunteered, those selected were chosen based in part on their military and emergency medical experience, Kelly said.
Traveling by bus and car, they will remain at least eight days, but many could be needed back soon afterward, he said. New York hosts the U.S. Open until September 11 and the U.N. World Summit begins three days later.
Three hundred New York firefighters also departed Monday for Louisiana from JFK Airport. The city sent 100 Metropolitan Transit Authority buses and 230 MTA personnel last weekend.