The Library of Congress has tentatively agreed with the family of Martin Luther King Jr. to acquire the civil rights leader's personal papers for $20 million. The purchase of the 80,000 items, which has to be authorized by Congress, would be the most expensive in the library's 200-year history.

Officials there have been interested in King's papers since before his assassination in 1968. The collection is of drafts of speeches, correspondence and other jottings that King made in the last six years of his life. Negotiations became active this summer when Librarian of Congress James Billington reminded Rep. James Clyburn (D-S.C.), the chairman of the Congressional Black Caucus, of the library's eagerness to acquire the King documents. Clyburn arranged a meeting in Atlanta with Dexter Scott King, head of the King Center for Non-Violent Social Change and one of the leader's four children, and Coretta Scott King, his widow.

"Mr. Billington made his case," Clyburn said yesterday, "and he said he understood that Sotheby's auction house had appraised the documents at $30 million. The King family said right then they would make a $10 million gift to the country." Sotheby's did a private appraisal of the archive at the request of the King family.

In most cases papers from such a prominent figure--from presidents to artists--would be given to a university or library. The papers to be acquired by the Library of Congress are now held at the King Center in Atlanta.

This archive is not the only collection of documents regarding King.

Not included in this deal is a collection of King's papers at Boston University covering the years before 1961. It includes 83,000 papers that King deposited there in 1964 and 1965. That archive was the focus of an eight-year custody battle between Coretta Scott King and the university that ended in 1995. Mrs. King argued unsuccessfully that her husband gave them to the university for temporary safekeeping, not ownership. Boston University was her husband's alma mater; he earned a theology doctorate there.

Scholars also have access to extensive declassified FBI records concerning King at the National Archives.

Clyburn said the King family was justified in selling the documents. "King--when he won the Nobel Peace Prize, he gave the money away. He didn't give it to his children. We don't hear a lot of people raising Cain about giving these ex-presidents pensions or money to build their libraries. When they gave the libraries the papers, they accumulated them while they were on the public payroll," he said. "The King family has made some significant contributions and sacrifices and I see this as a very small gesture on our part."

Gen. Donald L. Scott, the deputy librarian of Congress, said yesterday that "the library would welcome this collection of one of the century's great freedom fighters."

In a statement, Dexter King said the family preferred the Library of Congress as the repository of the papers for purposes of preservation as well as access. "If the papers were sold without regard for their preservation, they would probably bring untold tens of millions. After consultation with the King family, a decision has been taken to transfer the papers of Martin Luther King, Jr. to the Library of Congress for significantly less than these public estimates of worth."

The legislation authorizing the purchase does not include a specific price and was introduced by Clyburn on Sept. 28. The sponsors included Reps. J.C. Watts (R-Okla.), John Lewis (D-Ga.) and Cynthia McKinney (D-Ga.).

King has remained a symbol for racial and social justice in the three decades since his assassination in Memphis. He was the commanding and most prominent figure in the crusade to end segregation and racial discrimination in the '50s and '60s. In 1957 he helped found the Southern Christian Leadership Conference, a group of ministers who organized sit-ins and other peaceful demonstrations throughout the South. These clashes with the segregationists of the time were captured on film and shown on television, making King a powerful and universally recognized figure. In 1963 he delivered his "I Have a Dream" speech before 200,000 people at the Lincoln Memorial. The next year he was awarded the Nobel Peace Prize.

When the collection lands at the Library of Congress, Washington will have one of the most in-depth records of black political, artistic and intellectual life in existence. Howard University has one of the largest collections of African American archival materials in the world. The Library of Congress has the papers of abolitionist Frederick Douglass, labor leader A. Philip Randolph and Supreme Court Justice Thurgood Marshall. The records of the NAACP and the National Urban League are also housed there.

Clyburn said the Library of Congress is the proper place for the King material. "It is one place where every library in the country, every school in the country--as soon as we get them all wired--where everyone can have access," he said.

Though books, letters, photos and other material are often donated to the library, there have been instances when Congress appropriated money for strategic purchases. In 1815, $23,950 was earmarked to resurrect the library after it was burned in the War of 1812. The funds were used to acquire the vast and varied library of Thomas Jefferson. In 1864, Congress set aside $4,000 to buy European periodicals relating to the Civil War. Three years later the library laid out a whopping $100,000 for the Peter Force library, now considered one of its major collections. In 1930, the library made its priciest purchase to date, the Vollbehr Collection, for $1.5 million. It included one of three perfect vellum copies of the Gutenberg Bible, and some 3,000 other items.

Staff writer Linton Weeks contributed to this report.