Nagin announced last week New Orleans residents displaced by Hurricane Katrina and flooding Aug. 29-30 could start returning to the city Monday, one zip code at a time.
After emerging from a meeting of his Homeland Security Council, Bush said if necessary he would speak to Nagin personally to slow repopulation, the Washington Post reported.
"The mayor has got this dream about having his city up and running," Bush said. "We share that dream, but we also want to be realistic about some of the hurdles and obstacles. We have got concerns."
Bush's remarks followed similar comments by Coast Guard Vice Adm. Thad Allen, head of the federal government's hurricane response team, Sunday. Allen said it could be weeks before residents can safely return because of the lack of potable water, electricity, emergency services and concerns about the levees protecting the city.