When Franklin D. Roosevelt took office in 1933, in the depth of the Great Depression, he told the American people, “The only thing we have to fear is fear itself.” His firm leadership as president allayed the economic fears that gripped the country and used those fears to marshal support for drastic recovery measures. Later, when the Pearl Harbor attack triggered new fears, he used them to bring the United States into the war against the German-Japanese axis and to lead the country toward eventual victory.

President George W. Bush, too, had to manage fear when terrorists attacked the World Trade Center and the Pentagon and threatened other horrors against Americans at home and abroad. His firm, cool leadership built domestic support and an international coalition to break up the terrorist leadership in Afghanistan and overthrow the Taliban regime that had given it a home. Fear has helped, but that job is far from finished. And al-Qaida survives and plots new attacks around the world.

Fresh guerrilla fighting erupted last week in Afghanistan. Now that Mr. Bush has shifted his sights to Iraq, he has clearly been trying to transfer that same fear of terrorism to Iraq and focus it on Saddam Hussein.

Neither the American people nor the international community has fully bought the connection. United Nations inspectors disputed the president’s claim that Iraq has resumed its development of nuclear weapons, although they said they would need a few more months to offer “credible assurance” that a nuclear program was not in place. And the U.S. Central Intelligence Agency has continued to dispute the Pentagon’s insistence that Iraq has been cooperating with al-Qaida and played a part in the Sept. 11 attacks.

Hans Blix, the U.N.’s chief chemical and biological weapons inspector, has challenged Mr. Bush’s argument that military action is needed to avoid the risk of another terrorist attack like those in New York and Washington. He told The New York Times, “I think it would be terrible if this comes to an end by armed force, and I wish for this process of disarmament through the peaceful avenue of inspections. But I know that diplomacy needs to be backed by force and inspections need to be backed by pressure.”

Much will depend on whether Secretary of State Colin Powell can make a credible case to the U.N. Security Council today that Iraq is truly an imminent military threat and whether Saddam directly or indirectly helped destroy the World Trade Center and damage the Pentagon. Unless that case can be made, war should wait.