A day after mayoral candidate William Thompson, the city comptroller, proposed significant changes to the school system, Mayor Michael Bloomberg used his record on education to pick up another endorsement.

The mayor was in Harlem Wednesday morning to pick up an endorsement from the Reverend Calvin Butts of the Abyssinian Baptist Church.

Butts, who also endorsed the mayor back in 2005, spoke of improvements in education under Bloomberg.

However, the prominent reverend refused to go after the mayor's chief opponent in the race. In fact, he even heaped on the praise, leaving open the possibility that he might endorse Thompson in another campaign at some point down the road.

"I think Bill Thompson is going to make a tremendous contribution to this city and I encourage him in the future," Butts said. "And I must say, that I think he'd be a fine mayor. But now I believe that the best mayor to take us over the next four years is Michael Bloomberg."

Thompson, meanwhile, released an audit Wednesday, slamming the Metropolitan Transportation Authority for not moving fast enough to fix dangerous conditions in the subway system.

When asked Butts' endorsement of the mayor, Thompson said he still remains optimistic about his chances in November's election.

"There are a number of people who have endorsed the mayor. It doesn't mean their congregations are going to be supporting the mayor," said Thompson. "So I'm confident right now, that people all over the city are supporting my campaign. The list is growing each and every day and I am confident that we are going to win in November."