The combat phase of our war in Iraq ended with a speedy, decisive victory and minimal loss of life. That impressive success is now at risk. Our troops and administrators are coping with ethnic and religious rivalries, a long-repressed people, a war-damaged infrastructure already decayed from years of neglect and corruption, a lack of Iraqi democratic experience and a host of extreme clerics, looters, gangsters and warlords-in-waiting, all moving into a power vacuum.

The resolve of President Bush, the war plan of his team and the skill of our coalition military forces have delivered a once-in-a-generation opportunity to change the political landscape of the Middle East. Iraq has the ingredients to become a modern state: an educated population, a functional bureaucracy, a tradition of trade and industry and large reserves of oil to benefit its people. An Iraq transformed from tyranny to democracy can be a springboard for democratic reforms throughout the region and to end the pattern of autocracy and oppression that characterizes so many Arab governments. By demonstrating that we waged the war in the name of freedom, and not for conquest or oil, we will strike a blow against the pervasive anti-Americanism that fuels Islamic terrorism.

But transforming Iraq won't be easy, quick or cheap. Clearly, the administration's planning for the post-conflict phase in Iraq was inadequate. I'm concerned that the Bush administration and Congress haven't yet faced up to the true size of the task that lies ahead or prepared the American people for it. The administration should state clearly that we're engaged in "nation-building." We're constructing the future in Iraq. It's a complicated and uncertain business, and it's not made any easier when some in the Pentagon talk about quick exit strategies or say dismissively that they don't do nation-building. The days when Americans could win battles and then come home quickly for a parade are over.

The public and Congress need to know what we're getting into. Starting Thursday, the Senate Foreign Relations Committee held hearings to give the administration a chance to share its plans with the American people and to begin a debate on the important issues for Iraq's future. I want to see evidence that the administration is in this for the long haul to create a stable, democratic Iraq and to acknowledge that this will place a significant burden on the American people. Congress has already voted $2.5 billion toward the rebuilding effort. We've heard estimates that the final bill may be $100 billion. I believe the process may take at least five years.

The first question is: Do we have enough troops in Iraq? It may be that to restore law and order right now, we need to put more soldiers back into the country. In the medium term and longer, we have to look at the force structure: Does the Pentagon have the right kind of units for an interim stabilization force and later for peacekeeping, policing and police training? If not, who will provide them? What types of contributions should we expect from our allies? Only when aid workers and other civilians are safe from robbers and carjackers can we get on with feeding the people, repairing the hospitals and restoring the water and sewage systems. The Iraqis will respond positively if we can fix their infrastructure.

We also need to know the strategy for political transition. The original timetable of having an interim Iraqi government in place by early June seems unlikely. We must purge elements of the Baath Party leadership and prevent extremist Shiites, many of them linked to Iran and determined to establish a theocracy, from taking power — and we must do so without provoking an anti-American backlash. Some U.S. officials have talked of a two-year occupation, but they should note recent past experience. Seven years after the Dayton accords, 12,000 international peacekeepers are still in Bosnia.

It would be irresponsible — and contrary to our national security interests — to walk away from Iraq before it becomes a dependable member of the world community. We would provide an incubator for terrorist cells and activity. The American people know this. A recent poll by the Program on International Policy Attitudes found that an overwhelming 86 percent said the United States has "the responsibility to remain in Iraq as long as necessary until there is a stable government," and nearly as many, 73 percent, said pulling out prematurely "would be unwise and immoral."

President Bush should make clear that he will declare "Mission accomplished" in Iraq not on the basis of our military victory or the date of our withdrawal but on what kind of country we leave behind.

The writer, a Republican senator from Indiana, is chairman of the Senate Foreign Relations Committee.