... Johnson died in 1973, and no writer has done more to sustain the debate than Caro, whose three LBJ books have been praised, honored and condemned. His second work, "Means of Ascent," was so harsh a portrait that former Johnson aide Jack Valenti wondered why Caro bothered with a man "he thoroughly despises." The third book, "Master of the Senate," pleased Valenti so much that he reconciled with Caro, agreed to be interviewed for the fourth volume and even asked Caro to blurb his memoir, published last year.

Caro, lean and energetic at age 72, was interviewed recently in his midtown Manhattan office, a bright, businesslike array of legal pads, briefcases, file cabinets, outlines and heavily marked papers, all processed and sifted for his Smith Corona typewriter.

The historian says he has completed the opening section of his fourth LBJ book, filling hundreds of pages just to tell of Johnson's brief, unhappy vice presidency under John Kennedy, concluding with Johnson being sworn in as president after Kennedy's assassination. The last book will be "very long," although likely less than the 1,000-plus length of "Master of the Senate." He is reluctant to reveal details, but says the Kennedys will be "more than characters; they are protagonists in this book."...