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Two leading presidential candidates delivered dueling speeches during Sunday's commemoration of the 1965 civil rights marches in Selma, Ala., with Sens. Barack Obama and Hillary Clinton paying homage to those who helped break color barriers and enable black constituents to become a leading factor in possibly catapulting one of them to the Democratic presidential nomination for 2008.

Tapped in February to be the keynote speaker at the annual event held at Brown Chapel AME Church, where the marches began on March 7, 1965, Obama talked about how he directly benefits from the gains made during the civil rights struggle.

"This is the site of my conception. I am the fruits of your labor. I am an offspring of the movement," he said to a roaring crowd. "When people ask me if I've been to Selma before, I tell them 'I'm coming home.'"

Obama, whose mother is white and from Kansas and whose father is black and from Kenya, responded with aplomb after finding out earlier this week that his white ancestors owned slaves.

"That's no surprise in America," he said, adding that his mother's family was inspired by the struggle for civil rights. "I'm here because somebody marched for our freedom. I am here because you all sacrificed for me. I stand on the shoulders of giants."

Unwilling to let her competition get the better of the day, Sen. Hillary Rodham Clinton also appealed to African-Americans commemorating the day when black marchers defied a ban by Gov. George Wallace and headed across the Edmund Pettus Bridge only to be clubbed and attacked by local police. The ban was overturned two weeks later.

"We all know we have to finish the march," Clinton told parishioners at First Baptist Church, three blocks away from Brown AME. "That is the call to our generation."

Clinton, who appeared with her husband, former President Bill Clinton, a favorite among the black community after being dubbed America's first black president by writer Toni Morrison, said "Bloody Sunday" shocked the nation into action, and helped bring attention to racist practices that kept blacks from going to the voting booths.

"After all the hard work getting rid of literacy tests and poll taxes, we've got to stay awake because we've got a march to continue," Clinton said to applause and shouts of approval. "How can we rest while poverty and inequality continue to rise?

Sen. Clinton said the Voting Rights Act and Selma march opened up the way not only for Obama, but for her and Hispanic New Mexico Gov. Bill Richardson, who is also running for president.

Bill Clinton appeared alongside the senator in their first public outing together since she announced her candidacy. The former president is in town to be inducted into Selma's Voting Rights Hall of Fame, but his appearance is also meant to aide his wife, whose lead among African-Americans has shrunk since Obama entered the race.

The two candidates appeared outside Brown Chapel for a pre-march rally, but came from opposite sides of the podium and did not interact except briefly on the trail, when Obama approached Clinton to say a few words before stepping back to the other side of the street.

Despite the intense rivalry between their campaigns, the two praised each other. "It's excellent that we have a candidate like Barack Obama who embodies what all of you fought for here 42 years ago," Clinton said. Obama said Clinton is "doing an excellent job for this country and we're going to be marching arm-in-arm."

But they did not join arms when the commemorative march attended by thousands got under way. The Clintons marched together while Obama linked arms with the Rev. Joseph Lowery, who led the 1965 Selma-to-Montgomery march at the request of Martin Luther King Jr.

The two candidates sounded similar themes in their speeches — focusing on education, health care and the economy and blaming the Bush administration for failing to return Hurricane Katrina victims to their homes.

But Obama, who was three years old on "Bloody Sunday," delivered a call to action that would be politically unfeasible for Clinton or any of his other white rivals to make. He said the current generation of blacks does not always honor the civil rights movement and needs to take responsibility for improving their lives by rejecting violence; cleaning up "40-ounce bottles" and other trash that litters urban neighborhoods; and voting instead of complaining that the government is not helping them.

"How can it be that our voting rates dropped down to 30, 40, 50 percent when people shed their blood to allow us to vote?" Obama asked at a unity breakfast with community leaders.

At the breakfast, Obama got a key to the city and another to surrounding Dallas County from a probate judge, Kim Ballard. "Forty-two years ago he might would have needed it because I understand it would open the jail cells," Ballard said. "But not today."

Earlier Sunday, Hillary Clinton spoke to about 100 current and former public officials, ministers, lobbyists and party stalwarts at a private, invitation-only breakfast in Montgomery.

"You can't turn somebody into a Southerner who didn't grow up in the South like he (Bill Clinton) did," said former Secretary of State Nancy Worley, who attended the Clinton breakfast. "But she certainly did a good job showing her interest in people and her concern for people."

While the race between Obama and Clinton among African-American voters is narrowing, and the effort to appeal to black voters has pleased many civil rights leaders, Rev. Al Sharpton, who also was in attendance on Sunday, wondered what took Democrats so long to return to their base.

"I'm one of the crowd that comes every year, some folk come only when they need something. I come because I realize I got something," he said.

In fact, many in attendance on Sunday had been there before. Rep. John Lewis was among those beaten on the day of the banned march, which was followed up two days later by a separate march led by King Jr., and two weeks later by a five-day walk to Montgomery, the state capital. President Johnson signed the Voting Rights Act into law on Aug. 6, 1965. President Bush signed legislation extending it last summer.

Other Democratic candidates are not leaving the black vote to Obama and Clinton. John Edwards, the 2004 vice presidential nominee, was speaking about Selma and civil rights at the University of California, Berkeley.

"The fight for civil rights and equal rights and economic and social justice is more than just going to celebrations, even as wonderful as the one in Selma," Edwards said in remarks prepared for delivery as he referred to Berkeley janitors' fight for a wage increase. "The fight is going on right here, right now."

FOX News' Steve Brown and The Associated Press contributed to this report.