Under overcast skies, Mr. Bush joined former President Clinton and a host of civil rights figures and members of Congress to celebrate the monument to be built not far from where King gave his "I Have a Dream" speech in 1963.
"This project has been over a decade in the making," Mr. Bush noted. And he said he wanted to "particularly thank" Mr. Clinton, who signed the legislation authorizing the monument.
The president said that "on this ground, a monument will rise that will preserve his legacy for ages."
"When Martin Luther King came to Washington in December of 1963," Mr. Bush said, "he came to hold this nation to its own standards. ... He stood not far from here ... with thousands gathered around him. His dream spread a message of hope."
"An assassin's bullet could not shatter his dream," Mr. Bush said, noting the shooting that felled King in Memphis, Tenn., in April 1968.
Clinton| Bush| Oprah| Maya Angelou| MLK III| Barack Obama
"As we break ground, we give Martin Luther King his rightful place among the many Americans honored on the National Mall," the president said. "It will unite the men who declared the promise of America and defended the promise of America with the man who redeemed the promise of America."
The memorial, to be built roughly a half-mile from the Lincoln Memorial, where King gave his historic speech, will be the first monument to an African American on the Mall.
Mr. Clinton, in his remarks, said he was happy to have signed the legislation approving the monument in 1996. "It belongs here," he said.
The former president said the best way to honor King is to pursue his dream of equal opportunity for all.
Others present for the ceremony were poet and novelist Maya Angelou, television personality Oprah Winfrey, the Rev. Jesse Jackson, Secretary of State Condoleezza Rice and several members of Congress, including House Minority Leader Nancy Pelosi, D-Calif., and Sen. Barack Obama, D-Ill.
The 80-year-old Angelou had said in advance of the groundbreaking that the ceremony was even more special, coming almost a year after the death of Coretta Scott King, the civil rights leader's widow.
Donations for the memorial, which have mostly come from major corporations, hit $65.5 million earlier this month.
Harry Johnson, president of the Martin Luther King Jr. National Memorial Project Foundation, said he hopes to have the site completed by the spring of 2008.
The location is flanked by the Lincoln, Thomas Jefferson and Franklin D. Roosevelt memorials near the eastern edge of the Potomac River Tidal Basin. From a distance, visitors can see the stairs where King delivered his most famous speech during the March on Washington on Aug. 28, 1963.
The entrance to the memorial will include a central sculpture called "The Mountain of Despair." Its towering split rocks signify the divided America that inspired the nonviolent efforts of King and others to overcome racial and social barriers.