PRESIDENT BUSH last night set the United States on course for its most ambitious military campaign since the Vietnam War, one that should eliminate Saddam Hussein's illegal arsenal of weapons and replace his brutal regime with a representative government. Mr. Bush gave the Iraqi dictator and his sons 48 hours to leave the country. If they do not, he said, he will "apply the full force and might of our military." Mr. Bush warned Americans that the war might prompt terrorist attacks, either by Saddam Hussein or others; but he said that threat only underscores why action is necessary. Much of his televised speech was addressed to Iraqis: He warned Iraqi officers and soldiers not to commit war crimes or resist U.S. forces. To Iraqi citizens, he promised: "The tyrant will soon be gone. The day of your liberation is near."

Mr. Bush is right in insisting that Saddam Hussein face the "serious consequences" unanimously agreed upon by the United Nations Security Council in the event Iraq rejected a "final opportunity" to disarm. Though they agreed to those terms, France and Russia refused to respect them; they argued, as they did throughout the 1990s, that no forceful action should be taken against Saddam Hussein. In recent weeks their diplomats did their best to transform the United Nations' attempt to eliminate a rogue state's chemical and biological weapons into a global debate about the United States and its leadership -- and to a large extent, they succeeded. Whether their underlying intention was to protect the Iraqi regime or to create a political mechanism for containing the United States -- or, as they claimed, simply to avert war -- they made it impossible for the Security Council to act effectively. Their claim that no legitimate military action can take place without further U.N. approval, echoed by some Bush administration opponents in the United States, is groundless. The Security Council has explicitly sanctioned armed force only a few times in its history; most interventions have occurred without it, including several initiated by the Clinton administration and others by France. As Mr. Bush said last night: "This is not a question of authority, it is a question of will."

A number of countries likely will join the United States and Britain now in the Iraq campaign. Still, the war will be conducted with less support than the cause should have commanded. The Bush administration has raised the risks through its insistence on an accelerated timetable, its exaggerated rhetoric and its insensitive diplomacy; it has alienated potential allies and multiplied the number of protesters in foreign capitals. It also has refused to level with Americans about the human and financial costs of the coming war and the commitment the United States will have to make to postwar Iraq. Mr. Bush missed another opportunity last night to be clear about those costs; he persists with domestic policies that are entirely at odds with the demands of war, such as his huge and unaffordable tax cuts. We believe that the administration should work hard in the coming months to heal the rifts in the transatlantic alliance, invite international collaboration with the postwar Iraqi administration and honor the president's pledge to seek U.N. endorsement for that administration. It must also adjust its domestic policies to the realities of its foreign commitments.

For now, however, the priority must be to destroy the regime of Saddam Hussein, with as little harm to U.S. forces and noncombatant Iraqis as can be managed. No such campaign can be embarked on without trepidation; there are many risks, including, as Mr. Bush said, that the cornered dictator will use his horrific weapons, either on the battlefield or against civilians. But Iraqis, even more than Americans, have much to gain from the downfall of a tyrant guilty of some of the most terrible human rights crimes of the past half-century. A regime and an arsenal that have threatened and destabilized the Middle East for two decades can be eliminated; prisoners can be released, ethnic minorities freed from brutal repression, war criminals brought to justice, and a polity based on torture and murder replaced by one that respects basic political and human rights. That is the kind of cause that the United States has always embraced; it is a cause worthy of the sacrifices that will now be asked of American men and women in uniform.