Coretta Scott King, recovering from a stroke and heart attack she suffered last August, missed Monday's service at Ebenezer Baptist Church. 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.
Some of the speakers used the church pulpit where King preached from 1960 until his death in 1968 to criticize the Iraq war, saying that money being used by the military overseas could be put to better use domestically, such as to improve U.S. education, especially for blacks.
Atlanta Mayor Shirley Franklin said the city, as keeper of King's legacy, has a particular obligation to preserve his "legacy of fighting for social and economic justice, a legacy of marching with the poor and the neglected, a legacy of demanding peace against senseless war."
This year is the 20th anniversary of the federal holiday, first held on Jan. 20, 1986. Sunday would have been King's 77th birthday.
"This, Atlanta, is a time for rigorous and vigorous positive action," Franklin said. "As we celebrate, let us not confine our actions to what is easy, convenient or acceptable to the powers that be for we are called by King's legacy to bold, courageous, audacious, persistent and tireless action."
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."
Former U.S. Rep. Floyd Flake, pastor of the Allen African Methodist Episcopal Church in Queens, N.Y., said that King accomplished much for blacks in the United States but blacks today need to continue to strive for more.
"Why are we living like this when so many sacrifices have been made?" he said.
Flake urged blacks to make "everybody accountable" as King once did.
"Martin Luther King came on the scene at a time when there was a need to say, 'Don't read the tea leaves, read what is happening.' If we don't change things now we won't have the opportunity to change them in the future," Flake said. "The paradigm needs to shift and if the paradigm doesn't shift, we're still going to be coming MLK Day after MLK Day singing 'We Shall Overcome."'
The president peered through a glass case at the original Emancipation Proclamation, which was on display for just four days at the National Archives.
"It seems fitting on Martin Luther King Day that I come and look at the Emancipation Proclamation in its original form," Bush said. "Abraham Lincoln recognized that all men are created equal. Martin Luther King lived on that admonition to call our country to a higher calling, and today we celebrate the life of an American who called Americans to account when we didn't live up to our ideals."
Abraham Lincoln signed the document declaring the end of slavery in the midst of the Civil War on Jan. 1, 1863, and it is only occasionally brought out of storage because the poor quality of the paper and ink make it vulnerable to light.
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.
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.
"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."
U.S. Rep. John Lewis recalled the Rev. Dr. Martin Luther King Jr. on Monday as a man who brought hope in a time of hopelessness. Lewis, D-Ga., spoke at the 16th Annual Dr. Martin Luther King Jr. Holiday Breakfast in Minneapolis.
Lewis said he knew King personally and regarded him "as a brother, a friend, a colleague, a prophet, my hero, and just a simple human being filled with love, peace and compassion for all humankind."
Many of those who knew King can't help wondering what else he would have done, had his life not been cut so short.
"He was so eloquent. He was so brilliant. And had he lived, I think he would have probably been a university president or an ambassador," said Chuck Stone, a journalist, nationally syndicated columnist, author and teacher who developed a close relationship with Dr. King in the 1960s. "He might have even had a political career. There was no limit to what he could have achieved had he lived."
"He said, 'Don't mention me when I die. Don't mention my awards, my Nobel prize. Just say I tried to help somebody, I tried to serve,'" Stone recalled, in an interview with CBS News' Up to the Minute. "That was his joy and commitment, to serve and help people."
Elsewhere across the country, Americans marked the holiday with services and volunteer projects to aid communities.
In Columbia, S.C., hundreds 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, the day was marked with a Martin Luther King Day of Service: thousands of volunteers helping 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.