And he kept coming back to Vietnam - a blot on his Admiministration he wanted to remove. As an active candidate, he reasoned, he might miss or postpone an opportunity to achieve peace. ''What if we're late in the campaign and I have to make a decision that might result in a peace settlement but will be politically risky,'' he mused one night in March. ''I want my hands free to do what's necessary to end this thing.''

On Friday, March 29, the President said at a news conference that he would deliver a televised address the following Sunday evening. Friday evening, he called his press secretary, George Christian; Postmaster General W. Marvin Watson and me into his Oval Office study. The discussion lasted a couple of hours.

''I'm thinking about announcing Sunday that I'm not running. What do you think?'' he opened over the first drink. The three of us argued vigorously while he poked holes in each argument. By evening's end, we split 2-1 (George was against his running, Marvin and I said it was too late for him to step away from the battle.) We left the meeting not knowing what he would do.

Early Saturday morning, he told me to put Horace Busby back on the ''I will not run'' peroration. The rest of that day, the main speech, in which Mr. Johnson announced a unilateral halt to bombing in the top half of North Vietnam and deployment of only a fraction of the troops Gen. William C. Westmoreland had asked for, went through dozens of revisions before the late night final draft.

Early Sunday morning, he summoned me to the White House to accompany him and his daughter Lucy to mass at St. Dominic's Church. Lucy had converted to Roman Catholicism and Mr. Johnson took great solace in these church services. He often visited St. Dominic's, where the priests, whom he referred to as ''the little monks,'' would conduct a private service. During the service, he whispered to me to ask the Secret Service to get his speech from his bedroom and to call Vice President Hubert H. Humphrey, who was scheduled to leave that morning for Mexico City. At the Vice President's apartment in southwestern Washington, Mrs. Humphrey and Lucy visited while the President gave Mr. Humphrey the speech. When he got to the final paragraph, the Vice President's face flushed, his eyes watered and he protested that Mr. Johnson could not step down. Mr. Johnson pressed his right forefinger to his lips and admonished: ''Don't mention this to anyone until Jim calls you in Mexico tonight. But you'd better start now planning your campaign for President.''

Mr. Humphrey's facial expression was pathetic at that moment. Shoulders hunched, he said softly, ''There's no way I can beat the Kennedys.'' We departed.

Later that night, March 31, after the speech had been delivered, the President bounded from his chair in the Oval Office to join his family in watching the television reviews. His shoulders temporarily lost their stoop. His air was that of a prisoner let free.