The mayor of Atlanta called Monday for "bold, audacious" action to make sure society really heeds the message of the Rev. Martin Luther King, and urged listeners gathered to mark his holiday not to forget the victims of Hurricane Katrina.

"It is our time to step up to the plate as we have done in the past to lead this country and world by example," Mayor Shirley Franklin said at the King Day service at Ebenezer Baptist Church, where King preached from 1960 until his death in 1968.

This year is the 20th anniversary of the federal holiday, first held on Jan. 20, 1986. Sunday would have been King's 77th birthday.

Franklin urged listeners to "comprehend the full message of Dr. King" — by helping the young, the old and the poor and demanding more federal funding for Hurricane Katrina victims.

"Employ a homeless man or woman," she said. "Sponsor a homeless family. Give a convicted felon who has served his time another chance."

Hurricane Katrina debris along New Orleans' Martin Luther King Boulevard, a grassy median near a King statue and memorial, had been cleaned up in advance of the King Holiday parade that ended there Monday, but many nearby buildings remained abandoned and in ruins.

New Orleans Mayor Ray Nagin called on black people to rebuild the city, which was more than 60 percent black before Katrina displaced about three-quarters of its population.

"This city will be a majority African American city," Nagin told a crowd at City Hall. "It's the way God wants it to be. You can't have New Orleans no other way. It wouldn't be New Orleans."

Americans marked the holiday elsewhere across the country with services and volunteer projects to aid communities.

Hundreds of people in Columbia, S.C., crowded into Zion Baptist Church to kick off a march to the Statehouse for the annual King Day rally.

"Martin Luther King had a dream. Some 38 years later, how much progress have we really made toward living that dream?" the Rev. Charles Jackson told the crowd.

In Philadelphia, organizers of the Martin Luther King Day of Service expected thousands of volunteers to help with 600 projects in the area.

Among them: the building of a house that will be trucked to Lafayette, La., for a family made homeless by Katrina and construction of a two-story playground house. Volunteers also were working to provide meals to people living with HIV and AIDS.

Absent from the Atlanta service was King's widow, Coretta Scott King, who suffered a stroke and heart attack last August. She had received a standing ovation Saturday night when she appeared on stage with her children at an awards dinner, but she did not speak.

Last month, the board of directors of The King Center, located next to the Atlanta church, broached the possibility of selling the center to the National Park Service. But some King family members have been sharply critical of the idea.

Isaac Newton Farris, a nephew of King who is president of the King Center, is one of the supporters, and he mentioned the idea in his remarks Monday. Farris said the sale would help them "devote more resources — human and economic — to developing programs, not managing buildings."

"You still will be able to visit the King Center — we just won't own it," he said. "We want the King Center to be engineers of society, not engineers of buildings."