Only hours away from assuming the world's most powerful job, Barack Obama spent Monday urging Americans to work together, put aside their differences and serve their country.

"Tomorrow we will come together as one people on the same Mall where Dr. King's dream echoes still," said Obama in a statement Monday.

On the holiday honouring Rev. Martin Luther King Jr., Obama asked all Americans to mark the civil rights leader's legacy by making a renewed commitment to public service.

"His was a vision that all Americans might share the freedom to make of our lives what we will; that our children might climb higher than we would."

And it appeared Obama was striving to lead by example.

Earlier in the day, his motorcade stopped by an emergency shelter for homeless teens in Washington, where the president-elect grabbed a roller and helped paint the building's walls.

"These young people have future potential that right now is not being tapped," Obama told reporters as he painted alongside several young men.

"We can't allow any idle hands," said Obama, a former community organizer who worked in Chicago's impoverished south side. "Everybody's got to be involved."

'Loving service'

King, who pushed for equality through peaceful resistance, was assassinated in 1968.

Obama said King's "was a life lived in loving service to others."

"As we honour that legacy, it's not a day just to pause and reflect -- it's a day to act," Obama said. "I ask the American people to turn today's efforts into an ongoing commitment to enriching the lives of others in their communities, their cities, and their country."

"As we go forward in the work of renewing the promise of this nation, let's remember King's lesson -- that our separate dreams are really one," Obama said.

The Presidential Inaugural Committee even launched a website, USAService.org, to help people find opportunities in their area to volunteer.

Obama also put his pledge of non-partisanship into practice by praising his former presidential foe, Arizona Sen. John McCain.

At a dinner organized for McCain, Obama told the crowd that his one-time Republican rival is a "rare and courageous public servant.

"Let us strive always to find that common ground, and to defend together those common ideals, for it is the only way we can meet the very big and very serious challenges that we face right now," said Obama, who also planned to visit dinners for vice president-elect Joseph Biden and Colin Powell, the former Republican secretary of state.

Earlier Monday, Obama met with injured troops in an unscheduled visit to Walter Reed Army Medical Center.

'High Hopes'

Veteran White House reporter Helen Thomas, a columnist for Hearst Newspapers, compared the excitement ahead of Obama's presidency to that of former U.S. president John F. Kennedy.

"I do think we had great, high hopes for Kennedy but not to the magnitude that we're seeing now," Thomas told CTV's Canada AM on Monday.

She said Obama "better" live up to expectations.

"He has a large plateful of problems and I think that better not keep walking right down the middle, he has to be bold, he has to be courageous and I don't know if he is," she said.

She said the first 100 days after Obama takes power will set the tone for his administration.

"You have to be a visionary, you have to give a certain inspiration and that's what Kennedy did," she said.

In terms of crossing the colour lines, Thomas called Obama's presidency the "greatest thing" that's ever happened to America.

"It's going to be so transforming in our society, in our culture, how we look at people, how we treat people," she said.

With files from The Associated Press