NEW YORK - A copy of the Emancipation Proclamation signed by Lincoln and bought by Robert F. Kennedy, who drew inspiration from the document as he enforced civil rights legislation in the 1960s, is going up for auction and could fetch as much as $1.5 million.

Kennedy bought the printed copy of the 1863 document declaring all slaves "forever free" shortly after its centennial celebration at the White House. His widow, Ethel, is offering it for sale Dec. 10 at Sotheby's, the auction house told The Associated Press.

It's one of 48 printed copies signed by President Abraham Lincoln. About half are known to survive; 14 are in public institutions and another eight to 10 are privately owned, said Shelby Kiffer, Sotheby's senior specialist for historic American manuscripts.

The original, handwritten Emancipation Proclamation is in the National Archives.

Kennedy was attorney general to John F. Kennedy and served as his brother's closest adviser. He was elected in 1964 to represent New York in the Senate and was assassinated in California on June 6, 1968, while campaigning for president.

The fact that the Kennedy White House celebrated the document when RFK was in charge of civil rights enforcement "really brings this to life," Kiffer said.

"It also shows that you can have a spectacularly moving document, but it's the deeds that back up the words of the document that are just as important," he added.

Kennedy bought the copy, printed in black ink on acid-free paper, at a Sotheby's auction in early 1964 for $9,500.

In a speech at the White House centennial ceremony, Kennedy spoke of furthering Lincoln's work: "We have had a great deal of talk in the past 100 years about equality. Deed, not talk, is what is needed now. ... We must do more because nations which are free, people who would be free, look to us for leadership, not merely in strength of arms, but in strength of convictions."

The document marked a pivotal moment in Lincoln's presidency, and the country's, because it acknowledged that the Civil War was being fought to free the slaves.

Just before signing it, Lincoln said: "I never, in my life, felt more certain that I was doing right than I do in signing this paper."

A hundred years later, the United States found itself similarly torn over new laws enforcing black civil rights, and it was Robert Kennedy's job to carry them out.

"The Kennedy Emancipation Proclamation links the noblest ideals of the 1860s to the 1960s, links Robert Kennedy and Abraham Lincoln and civil rights and Civil War," Sotheby's Vice Chairman David Redden said.

Princeton journalism professor Evan Thomas, a historian, said he wasn't surprised that RFK would want to own such an important document.

"He enforced and pursued civil rights in a way that no one else in the attorney general's office ever had," he said. "He went down South and saw the injustice there, and he was determined to do something about it. ... He captured some of the spirit of Lincoln."

The document that Kennedy bought was framed and hung in one of the main hallways of Hickory Hill, his sprawling 1840s home in McLean, Va., that was sold last year. Ethel Kennedy declined to comment about the auction.

The copy was one of 48 signed by Lincoln and printed to raise money for medical care for union soldiers, Kiffer said. The RFK copy was first sold in the summer of 1864 at a Philadelphia fair held by the Sanitary Commission, a forerunner of the Red Cross. It will be exhibited in Boston, Philadelphia and New York prior to the auction.