When Taylor Branch began writing a history of the U.S. civil rights movement, he planned one book that would take three years.

Twenty-four years, three books, 2,849 pages and one Pulitzer Prize later, he has reached a historian's version of the promised land.

"At Canaan's Edge: America in the King Years 1965-68" (Simon & Schuster, $35), the final volume in Branch's monumental series, is out this month. The title, as with Branch's earlier works, "Parting the Waters" (1988) and "Pillar of Fire" (1998), comes from the Book of Exodus. The scope is nearly biblical, although the complex portrait of Martin Luther King Jr. is far from saintly.

Branch, who just turned 59, has mixed feelings about the end of what he calls "the blessing of a life's work." At his home in Baltimore, he feels "giddy, relieved, a sense of loss and a lot of nervousness about how much resonance the story still has."

The civil rights struggle still offers political and moral lessons, he believes, but he doesn't like to lecture. Branch prefers to be a storyteller, letting readers draw their own conclusions.

He does say that the more he has learned about King, the more he admires him, as a politician who never ran for office and as a preacher driven by a sense of guilt.

"He really was a threatening character," Branch says. "Many of those close to him were not comfortable with him, but his oratory transcended that. I found no one who criticized him for mixing church and state. He fused the language of religion and politics without being dogmatic about either."

Branch never met King, never even saw him speak or preach, although they shared a hometown: Atlanta.

As a teenager, Branch wasn't "blind to what was happening," but kept a safe distance from civil rights protests. He thought, "It was too scary, but maybe someday, when I was more established."

At 16, he watched TV coverage of protests in Birmingham, where 8-year-old black girls faced fire hoses and police dogs. "It was a pivotal moment," he said. "I remember my stupefaction, my questions about where did this come from?"

It's the same basic question his books aim to answer.

As a student at the University of North Carolina, Branch joined protests against the Vietnam War, not the civil rights movement.

Later, "my first original idea" was that anti-war activists "covered the civil rights movement the way Pat Boone covered Little Richard," using "cover" the way musicians do when someone sings someone else's song.

"We foolishly underestimated its complexity and need for discipline and self-sacrifice."

"At Canaan's Edge" reaffirms the radical power of nonviolence, but the book begins and ends with violence. It opens with a vivid description of armed Klansmen surrounding a black church in Lowndes County, Ala., in 1965. It ends three years later as King is assassinated on a motel balcony in Memphis: "King stood still for once, and his sojourn on earth went blank."

The book is a narrative with scores of characters, famous and little known. It constantly shifts from Selma to Vietnam, from the White House to turmoil within King's inner circle.

It deals with King's adultery and depression and with the FBI's campaign to harass and blackmail him. It mines President Johnson's secret White House tapes and the FBI's wiretaps of King. Branch says it's ironic that "something so evil would become so useful" to a historian re-creating that era.

In style and structure, Branch was influenced by Shelby Foote's "The Civil War," a three-volume, novel-like military history that "made you feel like you were part of it," Branch says.

Branch says he tried to make the story "as personal and as human as possible." He's not the first to reveal King's extramarital affairs but discloses that, in early 1965, King confessed to his wife, Coretta, about "the one mistress who meant most to him ... with intensity almost like a second family. The result was painful disaster."

Branch sees a connection "between one's private life and one's public life, but it's very complicated. I don't believe that because someone is a flawed philanderer, that makes that person a hypocrite in everything he does or says."

He also suggests that King's self-reproach and penance for his failure to give up his "illicit consolations" may have driven him to take risks he otherwise wouldn't have.

Branch isn't sure what he'll do next. He doesn't rule out a book about his friendship with Bill Clinton. They met in the student anti-war movement and jointly ran George McGovern's 1972 presidential campaign in Texas.

As president, Clinton asked Branch to help write his two inaugural addresses and to conduct a series of 89 late-night oral history interviews about his presidency that Clinton used when he wrote his memoir.

Branch ducks a question about comparing King's and Clinton's womanizing. He says he knows far more about King's private life than about Clinton's.

"It's strange. I feel I've spent much more time with King, whom I never met, than with Clinton, even though we had all that time together in the White House, just the two of us and a tape recorder."