File photo of Dr. Martin Luther King Jr., center left with arms raised, marches along Constitution Avenue with other civil rights protestors carrying placards, from the Washington Monument to the Lincoln Memorial during the March on Washington, Aug. 28, 1963 (Photo: AP)
President Barack Obama will lead his nation in homage Wednesday to Martin Luther King, at the spot where the civil rights icon voiced a soaring dream of equality 50 years ago.
In a moment of high symbolism, America's first black president will reflect on King's legacy and the long march, which still beckons to fulfill the hopes of the "I have a dream" speech, delivered from the steps of the Lincoln Memorial in Washington.
The event has thrown a spotlight on Obama's own historic story -- which he has said would not have been possible but for King's crusade to end racial discrimination.
But though his White House tenure marks a pinnacle of African American political achievement, some in the community have criticized the president for devoting insufficient time to a group plagued by deep social problems and barriers to advancement.
Obama made his name in part as a powerful speaker but he faces an almost impossible task to approach the eloquence of the off script "I have a dream" refrain in King's speech.
He said Tuesday he was still working on his own remarks but quipped "let me just say for the record right now, it won't be as good as the speech 50 years ago."
"When you are talking about Dr King's speech at the March on Washington, you're talking about one of the maybe five greatest speeches in American history.
"And the words that he spoke at that particular moment, with so much at stake, and the way in which he captured the hopes and dreams of an entire generation I think is unmatched," Obama said on the Tom Joyner radio show.
Obama argued that King, who was assassinated in 1968, would have been amazed at some of the progress since his remarks in 1963, including towards equal rights before the law for African Americans.
But he admitted that as King's March on Washington was about jobs, his fellow Nobel laureate would bemoan deprivation still felt by many blacks, especially in the inner cities.
"It's not enough just to have a black President ... the question is, (can) the ordinary person, day-to-day, can they succeed?
"And we have not made as much progress as we need to on that, and that is something that I spend all my time thinking about, is how do we give opportunity to everybody so if they work hard they can make it in this country."
Obama has sought to ensure that though he is the first black president of the United States, his administration should not be defined by race.
He argues that he is the president of all Americans. On only a few occasions since taking office has Obama stepped up and addressed his nation's scarred racial past and sometimes uneasy present.
In his most direct intervention, just weeks ago, he gave an unusually sweeping discourse after a trial into the killing of a black teenager in Florida.
"Trayvon Martin could have been me 35 years ago," Obama said of the victim, voicing anguish felt in the black community over what many see as racial profiling of many young African American men.
As part of the commemorations of King's speech on Wednesday, church bells will ring across the country.
An estimated 250,000 people of all races descended on Washington's Mall on a sweltering August 28, 1963 day, chanting "Equality now!" and singing "We Shall Overcome," in what was officially billed as the March on Washington for Jobs and Freedom.
Millions more watched on television -- among them president John F. Kennedy, who until then had been dragging his feet on legislation to end racial segregation in conservative Southern states.
King, 34, was the last speaker of the day.
Departing from his prepared text, he famously declared: "I have a dream that one day this nation will rise up and live out the true meaning of its creed: 'We hold these truths to be self-evident: that all men are created equal'."
The march helped set the stage for the Civil Rights Act of 1964 that outlawed major forms of racial discrimination, followed a year later by the Voting Rights Act designed to guarantee the franchise for all black US citizens.
The future of that law has been called into question after the US Supreme Court told Congress earlier this year to rewrite a key section regarding federal oversight of voting practices in mainly Southern states.
Wednesday's event, known as the March for Jobs and Justice, will also include former presidents Bill Clinton and Jimmy Carter and luminaries of the African American community.