Nagin's pledge put the Illinois senator ahead of rival Sen. Hillary Clinton, D-N.Y., in the battle for superdelegates, The (New Orleans) Times-Picayune reported.

"Since the immediate days following the storm, I have been traveling to our nation's capitol to advocate for policies that aid our rebuilding effort," Nagin said in a statement released by the Obama campaign. "I know first hand, we desperately need the leadership of someone committed to changing the system in Washington that can hold us back from moving forward."

Nagin spoke with Obama and Clinton last week and discussed the city's Hurricane Katrina recovery issues that drove his decision, including upgrading the nation's emergency response systems and removing "roadblocks" that hinder communities' recovery efforts after a disaster, Nagin spokeswoman Ceeon Quiett said.

"At the end of the day, the mayor was most conformable with Senator Obama," she said.