From WaPo:
Behind the scenes, a power struggle emerged, as federal officials tried to wrest authority from Louisiana Gov. Kathleen Babineaux Blanco (D). Shortly before midnight Friday, the Bush administration sent her a proposed legal memorandum asking her to request a federal takeover of the evacuation of New Orleans, a source within the state's emergency operations center said Saturday.
The administration had sought control over National Guard units, normally under control of the governor. Louisiana officials rejected the request, noting that such a move would be comparable to a federal declaration of martial law. State authorities suspected a political motive behind the request.
So then his declaration of a state of emergency was useless rhetoric