President Bush says the presidency is hard work and that the most important decisions are often not politically popular.

Sen. John F. Kerry replies that the president is devious and stubborn, most notably and tragically when he is wrong.

Both combatants should find comfort in"Decisions That Shook the World," a three-part Discovery Channel series that, starting tonight, dissects presidential decision-making at its most crucial and, at times, most devious and controversial.

Presidential historian Michael Beschloss, also co-producer of the series, notes in his introduction that in this presidential election season questions about the presidency and its enormous power are paramount.

"Decisions" looks at three cases of presidential leadership: Lyndon B. Johnson's decision to champion civil rights despite opposition from his fellow Southerners; Ronald Reagan's insistence on the"Star Wars" missile defense system when many people thought he was daft; and Franklin D. Roosevelt's determination to bootleg help to the British even before the U.S. entered World War II.

American presidents are finaglers,"Decisions" tells us. They sometimes ignore public opinion or uncomfortable facts when they think that the survival of the nation is at stake. They're politicians. They bully, seduce and flatter the opposition, foreign or domestic. They are routinely vilified by opponents as the most dire threat to the republic since its creation. One film clip shows a 1940 protester outside the White House with a sign,"Hitler Has Not Attacked Us -- Why Attack Hitler?"

If the much-praised"American Experience" on PBS is a graduate seminar on American history,"Decisions" is an undergraduate survey course -- but a good one with compelling film clips, a well-argued thesis and a sprinkling of insider-interviews.

The series starts with Johnson's decision, almost immediately after assuming office, to take up the civil rights legislation of his fallen predecessor and make it the highpoint of his administration.

Although Johnson had shown little interest in civil rights during his years in the Senate -- and routinely used the N-word -- he changed virtually overnight. Washington power broker Vernon E. Jordan Jr. tells viewers that when it comes to civil rights he would rather have a" converted Southerner than a wobbly Northern liberal."

It is a sympathetic portrayal of Johnson. Vietnam, where the same presidential steadfastness marched the nation into a quagmire, is given only a glancing reference. But survey courses are broad brush, and the focus of"Decisions" is on the civil rights and the voting rights bills.

Next week's episode, on Reagan and"Star Wars," may be the least compelling. On this one,"Decisions" could have used some dissenting or contrasting views. The argument that the threat of"Star Wars" pushed the Soviet empire to collapse is just that, argument.

Still, there is a good, if somewhat hagiographic, look at Reagan's personality."There was a stubbornness to Reagan when he thought he was right," says Michael K. Deaver. It's an insight that contradicts the widely accepted idea that Reagan was easily manipulated by his staff.

The best of the three episodes details Roosevelt's silent vow to help the British in the face of American isolationism and a strong challenge in the 1940 election by Wendell Wilkie. FDR may have been the wiliest man in the Oval Office.

"In 1940, Franklin Roosevelt knew he might have to skate to the edge of telling untruths or even breaking the law," Beschloss says."He didn't want to do it, but if it was necessary, he was ready." Roosevelt promised voters,"I will never send your boys to a foreign war," knowing full well he would someday do just that.

He had"an enormous self- assurance that allowed him to feel he always knew what was best, even when he was wrong," Beschloss says. He stepped on civil liberties. He quietly authorized wiretapping when it was still outlawed by the Supreme Court.

"Whenever he faced a question of liberty vs. security, he would choose security," said historian and Roosevelt biographer James MacGregor Burns.

If there is one thing that all three presidents in"Decisions" shared, it is a mastery of the stage. Which brings us back to where the series begins: politics and the national stage, with two men passionately promising to make different decisions on our behalf. On Nov. 2, the public will make its own decision.