The United States will face enormous challenges in a post-Saddam Hussein Iraq, as well as broad regional questions that must be addressed. These are both matters that members of the Senate Foreign Relations Committee have been focusing on for some time. During a week-long trip to the region, we came away with a better understanding of the possibilities and perils that lie ahead.

In northern Iraq we saw the extraordinary potential of Iraqis once they are out from under Saddam Hussein's murderous hand. New hospitals, schools, roads and lively media are testimony to the determination of Iraqi Kurds and to the bravery of coalition air crews patrolling the no-fly zone.

Just a few hours' drive from the oppressive rule in Baghdad, a freely elected regional government and legislature (which we were honored to address) are embarked on a path of clear-eyed realism. While neighboring countries fear an independent Kurdistan, Kurdish leaders appear committed to working together for a united Iraq. They realize they could lose everything they have built in the past decade by pursuing independence.

Although no one doubts our forces will prevail over Saddam Hussein's, key regional leaders confirm what the Foreign Relations Committee emphasized in its Iraq hearings last summer: The most challenging phase will likely be the day after -- or, more accurately, the decade after -- Saddam Hussein.

Once he is gone, expectations are high that coalition forces will remain in large numbers to stabilize Iraq and support a civilian administration. That presence will be necessary for several years, given the vacuum there, which a divided Iraqi opposition will have trouble filling and which some new Iraqi military strongman must not fill. Various experts have testified that as many as 75,000 troops may be necessary, at a cost of up to $20 billion a year. That does not include the cost of the war itself, or the effort to rebuild Iraq.

Americans are largely unprepared for such an undertaking. President Bush must make clear to the American people the scale of the commitment.

The northern Iraqi city of Kirkuk is an example of the perils American forces may encounter. It sits atop valuable oil fields and is home to a mixed population of Arabs, Turkmen and Kurds. In recent years, Saddam Hussein has expelled Turkmen and Kurds as part of an "Arabization," or ethnic cleansing, campaign. We toured a refugee camp housing 120,000 displaced people and heard countless stories of brutality and the loss of loved ones. Kirkuk could become the Iraqi version of Mitrovica, the volatile city in Kosovo where the U.N.-led administration has faced the dilemma of forcibly resettling people from various ethnic communities who have been evicted from their homes.

This is one reason why we will need our allies to help rebuild Iraq. Cementing a broad coalition today will keep the pressure on Hussein to disarm, build legitimacy for the use of force if he refuses, reduce the risks to our troops and spread the burden of securing and reconstructing Iraq. Going it alone and imposing a U.S.-led military government instead of a multinational civilian administration could turn us from liberators into occupiers, fueling resentment throughout the Arab world.

Iraq cannot be viewed in a vacuum. Disarming and stabilizing that country will be all the more difficult because of the unsettled regional environment, in particular the Israeli-Palestinian conflict. While it is essential that the United States aggressively pursue Israeli-Palestinian peace on its own merits, doing so has ancillary benefits for the disarmament of Iraq. Simply put, we will make it easier for Arab governments to participate in, or at least support, our actions in Iraq if they can show their people we are engaged in the peace process.

Meetings with Israeli officials and Palestinian reformers led us to believe new opportunities exist for American diplomacy. Recent polling shows that nearly three-quarters of Israelis and Palestinians seek reconciliation and a two-state solution. For the first time since the violence began, a majority of Palestinians support a crackdown against terrorism as part of a peace process. A large majority have no confidence in Yasser Arafat.

The key is to empower Palestinian reformers and encourage Arab moderates. President Bush should lose no time in publicly endorsing the "road map" developed by the Quartet -- an informal group of mediators on the Middle East from the United States, the United Nations, the European Union and Russia. The road map provides for a series of reciprocal steps to jump-start a renewed peace process. That would give hope to Palestinian reformers and send a clear message to the Arab world that the United States remains determined to pursue an Israeli-Palestinian settlement even as we deal with Iraq.

Working on multiple fronts poses a difficult test for American leadership, but there is no escaping the fact that we face several related, interlocking crises in the region. As the bulwark of freedom and democracy, the United States faces the need to disarm Saddam Hussein and set the stage for a stable Iraq, win a protracted war on terrorism and engage fully on the Israeli-Palestinian conflict. Working with our friends and allies, it is a challenge we can, and must, meet.

Sen. Joseph R. Biden Jr. (D-Del.) is chairman and Sen. Chuck Hagel (R-Neb.) a senior member of the Senate Foreign Relations Committee.