Mayor Bloomberg took his State of the City address on the road for Martin Luther King Day, testing out his key themes from last week’s speech on the stump before largely African-American audiences from Crown Heights to Harlem.

“Martin Luther King said we should never look back, we should always look forward,” Mr. Bloomberg told 600 volunteers repainting P.S. 75, in the Crown Heights section of Brooklyn. “Opportunity really is knocking for people in this city right now.”

Historically, Martin Luther King Day has been a challenging day for Mr. Bloomberg, a billionaire Republican in a city where registered Democrats outnumber Republicans five to one. He does not enjoy wide support in the city’s black communities but goes to them anyway, knowing he will receive, at best, a lukewarm reception. Lines that receive raucous applause in white bastions of the city have often elicited jeers or uncomfortable silence in black neighborhoods.

Public-opinion polls indicate Mr. Bloomberg is trailing Democratic rivals among black voters. He received about 25% of the black vote in 2001. According to the latest Quinnipiac poll, he now has a 46% unfavorable rating among black voters, while only 37% of the African-Americans surveyed said they approved of the job Mr. Bloomberg was doing.

Even so, Mr. Bloomberg has gone to their assemblages every Martin Luther King Day, telling residents he hasn’t forgotten them and will work to improve their communities. He rolled out proposals that were in his State of the City address last Tuesday.

The question of his personal wealth dogged him wherever he went. Usually it is an issue that comes up only occasionally during his public events as mayor. When Mr. Bloomberg arrived at the Interfaith Service at the Convent Avenue Baptist Church late yesterday, however, his billionaire status was alluded to before he himself was.

“The money is in the house, the money is in the house,” the pastor emeritus of the Community Baptist Church of Bayside, Rev. Samuel Joubert Sr., joked from the pulpit when Mr. Bloomberg arrived at the Baptist Ministers’ Conference of Greater New York. Then the minister laughed and said, “The mayor is in the house.”

Mr. Bloomberg blushed, took a crisp folded bill out of his jacket pocket – with the denomination discreetly hidden in the folds – and dropped it into the offering basket with a tight smile.

When the mayor talked about education reform and improving the public schools at the Brooklyn Academy of Music yesterday, a reference that received a standing ovation last week during his speech in the Bronx, audience members jeered.

“Fund it!” several women yelled from the darkness when he mentioned the schools.

“Pay the teachers!” another voice said.

Mr. Bloomberg pretended not to notice and plowed ahead. He talked about his favored West Side development project, which would, among other things, create a new Midtown business district with office space and parks next to an expanded Jacob K. Javits Convention Center and a possible new Jets football stadium. That project, controversial with most audiences, inspired some hisses and jeers yesterday.

By far the most difficult venue for the mayor during the past three Martin Luther King Day celebrations has been Canaan Baptist Church of Christ in Harlem, known as the “House That Al Built.” Every year that he has been mayor, Mr. Bloomberg has attended an annual rally with the Reverend Al Sharpton and members of the National Action Network. Mayor Giuliani was famous for snubbing the event.

“Reverend Sharpton, thank you for inviting me, and I look forward to coming here as mayor and I look forward to doing that for the next four years after this,” Mr. Bloomberg began yesterday, to derisive laughter from the crowd. “I welcome having the opportunity to describe today how my administration is striving to meet the challenges so the doors of opportunity can be open to all of God’s children.”

He proceeded to mention that construction of two hotels would soon begin in Harlem and his latest school reform plan included vocational training and broader programs for the gifted and talented, so it would serve all the city’s neighborhoods. The suggestions were met with uncomfortable silence.

“We’re not going to leave anybody behind. We have failed many of our children too long,” Mr. Bloomberg added, helpfully.

Unfortunately for a mayor seeking re-election on the changes he has made in the city’s schools, that line got applause.