After years of feuding, Martin Luther King's papers to be auctioned

The documents are being put on sale as a single lot by Dr King's estate, and his four children are expected to share the bulk of the proceeds, expected to be between $15m (£8m) and $30m. A portion of the sale price will go to the non-profit King Centre in Atlanta which keeps other documents and memorabilia.

"Our family wants to make sure the legacy of Martin Luther King is protected and preserved for generations for come," said the civil right leader's eldest son, Martin Luther King III.

But despite the stated intention of the family, the sale by Sotheby's on 30 June is likely to do little to settle the controversy that has surrounded Dr King's family and what some critics have seen as their willingness to cash in financially on his legacy. Three years ago when the family previously tried to sell the papers but failed to find a bidder, one American newspaper columnist, Cynthia Tucker, wrote: "These days it is increasingly difficult to remember that the King family was once held in such high esteem. They are mostly known now for their relentless profiteering. The heirs have converted King's legacy into a profit centre - I Have a Dream Inc."

Included among the papers are a draft of his 1964 Nobel Prize acceptance speech and an annotated copy of "Letter from Birmingham Jail", the open letter he wrote in 1963 after being arrested at a peaceful demonstration in the Alabama city at the centre of the civil rights struggle. There is also a programme from Atlanta's Ebeneezer Baptist church on which he had scribbled notes about the shooting of President Kennedy in Dallas.

Of most interest, perhaps, is a draft of the speech Dr King delivered to civil rights campaigners gathered at Washington's Lincoln Memorial on 28 August 1963, in which he declared: "I have a dream that one day even the state of Mississippi, a desert state, sweltering with the heat of injustice and oppression, will be transformed into an oasis of freedom and justice. I have a dream that my four children will one day live in a nation where they will not be judged by the colour of their skin but by the content of their character. I have a dream today."

Remarkably, the typed draft of that speech - prepared by Dr King at the city's Willard Hotel the night before his delivery - does not include the phrase "I have a dream". Instead, he added it extemporaneously as he addressed the crowds the next day, with police looking on and a federal official standing by to pull the plug on his microphone if it was thought his comments were likely to "incite violence".

A year later the Civil Rights Act was signed into law by President Lyndon Johnson and 13 months after that the Voting Rights Act was passed.

Also included among the papers to be sold are documents discovered in Dr King's briefcase after his assassination at a motel in Memphis, Tennessee, in 1968, and correspondence with other black leaders, including Malcom X, who offered him armed support to counter threats of violence. Dr King declined the offer.

Clayborn Carson, editor of the King Papers Project at Stanford University, told The Atlanta Journal Constitution: "These are certainly of major significance because Martin Luther King was at the centre of one of the most important transformations of American history, and so the documentation of that role is very important."

The family of Dr King has long been accused not just of making money from his legacy but also limiting the access of scholars to many of his most important papers. As well as signing licensing deals to sell copies of his speeches and even to use part of them for a telephone commercial, the estate has also aggressively challenged anyone seeking to use any of his work without a licence. The estate has sued the USA Today newspaper, for instance, for reprinting the "Dream" speech in full and CBS for using extended excerpts of the speech, which it had originally broadcast live on that sweltering 1963 evening.

What is not clear is the impact on the sales plans of the death five months ago of Dr King's widow, Coretta Scott King. She had long sought to sell the papers to a museum, library or university rather than to a private individual.

Whoever buys the papers will decide their future accessibility to historians and scholars. In 2003 the family agreed to a so-called private treaty with Sotheby's to sell the papers. The anticipated sale price at the time was $20m but the auction house failed to find a buyer. Sotheby's remains convinced of the value of the documents. Its vice-chairman, David Redden, said: "This collection is without question the most important American archive of the 20th century in private hands.

"Thirty-eight years after his death, Martin Luther King remains a heroic figure of inestimable importance, not only to Americans but to people around the world."