Baghdad has fallen, and the world's attention is turning to the rebuilding of Iraq. The United States has a vital interest in helping to create a stable, prosperous Iraqi government that renounces weapons of mass destruction and support for terrorism, does not threaten its neighbors and respects the rights of its people. Meeting this goal will require from the United States a multiyear, multibillion dollar commitment.

President Bush should continue and expand his efforts to explain the rationale for postwar American engagement in Iraq and to describe the extent of the required commitment. Financially, this could amount to about $20 billion annually for several years. Keeping 75,000 troops in Iraq will cost the United States about $17 billion a year, and reconstruction and humanitarian assistance could cost several billion more.

Some have suggested that Iraq's oil wealth can defray these costs. But much of that wealth has in recent years been allocated to the United Nations Oil for Food Program, which has sustained 60 percent of the population, and now oil revenues will again be needed to pay for food. Although increased oil production could yield more revenue, major increases are years (and many dollars) away. Moreover, those oil revenues cannot realistically be spent on supporting American troops; the United States will have to pay for the troops itself.

American objectives in rebuilding Iraq cannot be realized without public security. The experience of the Balkans and elsewhere has shown that the collapse of tyranny often unleashes violence, as security forces vanish and aggrieved groups settle scores. In Iraq, Kurdish, Shiite and other long-repressed groups may take it upon themselves to redress old injustices. And if the looting of recent days expands well beyond attacks against symbols of the former regime, Iraqis could begin to question the value of the American presence, and American goals could be put at risk. The United States military cannot take a hands-off approach to criminal acts, and should quickly deploy forces to cities and towns to prevent acts of reprisal and other lawlessness. The administration should also recruit constabulary forces from other governments to help maintain public order and begin to build a new Iraqi police force.

The involvement of the United Nations and its agencies like the World Food Program and the High Commission for Refugees would both lighten America's financial load and diminish the mistaken impression that the United States seeks to control postwar Iraq. It is possible for the United States to oversee security and civil administration in Iraq while giving the United Nations and other organizations significant roles in humanitarian aid, the development of a new government, Oil for Food, and reconstruction.

Finally, United States will have to ensure that Iraqis themselves are involved in the transition. Baathist leaders who served as instruments of the toppled regime's repression will have to be excluded, but otherwise Iraqis should continue to play key roles in the administration of government institutions. The quick resumption of basic services -- communications, transport, sanitation -- is essential and will require the work of thousands of civil servants. Every effort should also be made to promote Iraqi involvement in the transition to a new government, with Iraqis increasingly taking responsibility for governance. While returning exiles have a role to play in Iraq's future, the administration should continue to resist the temptation to anoint them alone as the new leadership. This would be undemocratic and could alienate important parts of the Iraqi population.

Peace-building can be extraordinarily complex. In Iraq, success will depend on America's willingness to adapt to changing circumstances and its determination to stay the course. The United States must commit substantial money and troops, ensure the active participation of other governments and international organizations, and involve the Iraqis in a process that meets their hopes for a brighter future.