THE ROMANS had a phrase: Carpe Diem. Seize the day. Shakespeare said it differently: "There is a tide in the affairs of men which if taken at the flood leads on to fortune." Whatever one may say of Lyndon Johnson, he absorbed the lesson of Carpe Diem at flood tide. Never was his daring more amply illuminated than in the drama that produced the Voting Rights Act of 1965.

During the long night of Nov. 22, 1963, a scant 12 hours after a young president was slain in the streets of Dallas, the new president was pajama-clad, lying in his huge bed in his Washington home. With him were three trusted friends, the late Cliff Carter, Bill Moyers and me. For more than four hours we sat with him, watching television, hearing the world speculate about who this Lyndon Johnson was and how America would fare under his leadership. What the commentators did not know was that in that solemn evening, LBJ was already shaping what came to be known as the Great Society -- including an extraordinary political revolution that would both exult and divide the nation.

LBJ had long nourished the idea of smashing all barriers that denied entry into voting booths for millions of Americans. I remember him saying that evening, "If you give folks the vote, they will soon have political power. And if you have political power, you can win whatever you want to make a better life for you and your family."

He knew it wasn't going to be easy. He knew he was putting his political future to extreme risk, menacing all of his other plans. The legislative path he would take to pass the Voting Rights Act would be mean, rough, thick with hazard. And first, he had to win passage of a pending civil rights bill to prohibit discrimination in jobs, schools, public accommodations and voting. So several weeks into his presidency, he confronted his closest friend and most resolute civil rights adversary, the patrician senator from Georgia, Richard Russell.

I sat with them that day, Russell and LBJ, there on the second floor of the White House, the living quarters. LBJ leaned toward Russell and said, "Dick, I love you, I owe you. But I'm going to run over you if you challenge me or get in my way. I aim to pass the civil rights bill, only this time, Dick, there will be no caviling, no compromise, no falling back. This bill is going to pass."

Russell was silent for a moment, and he said, in those softly rolling tones, "You may do just that, Mr. President. But I am here to tell you that it will not only cost you the South, it will cost you the election."

The president listened intently. Then he spoke, very quietly: "Dick, my old friend, if that's the price for this bill, then I will gladly pay it."

So the battle was joined, and the president won. The Civil Rights Act of 1964 was passed. But LBJ had a more spacious agenda. He wanted legislation that would permit direct federal action to enable blacks to register and vote, rather than piecemeal assistance to individuals. Like every shrewd commander, he waited for that decisive moment, for that tide to be taken at the flood. Several times in early 1965 he talked quietly with the black leadership -- with his old friend and trusted ally, Roy Wilkins, executive director of the NAACP; with the Rev. Martin Luther King Jr.; with another loving friend, Whitney Young, head of the Urban League; with Phil Randolph; with his friend of the longest time, Rep. Clarence Mitchell of Maryland. But he knew the time was not yet ripe.

Finally the moment appeared. It came at the Edmund Pettus Bridge early on the evening of March 7, 1965, in a sleepy little Alabama town called Selma. The night was scorched by brutal beatings of civil rights marchers en route to Montgomery, acts of savagery that flamed across the land on television and horrified millions of Americans.

And then again fate intervened to give ascendancy to LBJ's plans. On March 13, Gov. George Wallace of Alabama sought a meeting with the president. And he got it, fast. Exactly 24 hours after Wallace's request to meet was received, that dour-faced governor was in the Oval Office. The president proceeded to take Wallace apart, told him how history would treat him if he refused the basic decencies; told him the Constitution could not be torn apart and, if it was, he -- Wallace -- would be the culprit; told him that the president had 700 troops on alert and, by God, he would dispatch them without a second's lag if Wallace could not keep order; told him if those troops went down to Alabama, no one in the state better fool around with trying to evade responsibility. As the governor departed, he offered a furtive glance and a thin smile to me and others. The chastened Wallace plainly had not anticipated the Johnson treatment or its impact.

What LBJ didn't tell the governor was that the voting rights bill was nearing final draft form. The moment for LBJ was at hand. Two days later, on March 15 at 9 p.m., the 36th president of the United States "rose to testify" before a joint session of Congress. Few Americans who were of impressionable age at that time will forget the stunning Johnsonian declaration: "And we shall overcome!"

The president exiled rest and sleep from the White House. He deployed all his assistants to Capitol Hill. Applying both a whip and a carrot, we roamed the corridors. I told one Southern congressman: "You can't be left behind on this vote." He knew that tug at his lapel carried two meanings. You are either with us or against us. Either way is burdened with risk, but it's better to be with us.

On Aug. 6, 1965, LBJ signed the Voting Rights Act in the Rotunda of the Capitol. But for me the climax came three days earlier when Roy Wilkins and other civil rights leaders visited the Oval Office to celebrate passage of the act. With each, there was an air of religious jubilance in their embrace of the president.

I walked out of the West Wing with Wilkins after his visit. He put his arm around me and said: "Jack, God does move in strange and wondrous ways." I looked puzzled, and he said: "Don't you see? The bravest, most effective friend the Negro in America ever had turns out to be a Southern president."

Jack Valenti, president of the Motion Picture Association of America, was special assistant to President Johnson.