MICHAEL Nutter has stepped down as chairman of the Convention Center Authority, saying he needs to focus solely on his mayoral campaign.

"I've got four weeks to go in this race. I've got to give every waking and sleeping moment to what I'm doing here," said Nutter, who sent a resignation letter to Convention Center board members Tuesday.

The Convention Center Authority, which appointed Nutter to the unpaid position of chairman in 2003, is in the midst of planning a $700 million expansion.

Convention Center Executive Director Al Mezzaroba said he had asked Nutter to stay, but Nutter told him he couldn't balance his Convention Center responsibilities and campaigning.

"Michael's one of those guys that has to put 100 percent into what he does," Mezzaroba said.

He praised Nutter's four years at the authority.

"I will say Michael stayed devoted to this thing . . . although his time got tighter, there was never a time when I couldn't get him on the phone," Mezzaroba said.

Mezzaroba said the vice chairman, Thomas "Buck" Riley, will fill in for Nutter until a new chairman is appointed. He said the board could vote on a chairman at its next meeting, May 23.

Nutter's appointment to the Convention Center came out of a controversial 2002 retooling of the authority by Republicans. *