SECRETARY OF STATE Colin L. Powell's visit to Turkey today offers an opportunity to begin repairing U.S. relations with an essential Muslim ally. The Turkish parliament's refusal to allow a U.S. division to pass through the country on the way to Iraq has complicated the U.S. drive on Baghdad and stirred bitter feelings in Congress, where an administration request for wartime aid for Turkey has been challenged. But the new democratic government in Ankara is feeling the pain as well: The loss of goodwill in Washington comes in addition to a series of recent diplomatic and economic reverses that have placed Turkey's strategic orientation toward the West at risk. There has been fault on both sides, by an inexperienced new leadership in Ankara and by a U.S. administration that allowed military logisticians to dictate the pace of what should have been more careful prewar diplomacy. But Turkey, unlike France, has no wish to form a bloc opposing the United States; and both Turkey and the United States have much to gain by restoring a close working relationship.

One place to start is northern Iraq, where the absence of a significant military thrust against Saddam Hussein's forces has been partly balanced by U.S. success in maintaining equilibrium in a potentially volatile area. Turkey so far has restrained itself from sending troops across the border into Kurdish-populated areas, an action that might ignite clashes with U.S.-allied Kurdish militias; U.S. commanders have in turn restrained the Kurds from steps that might provoke Turkey. A central aim of Mr. Powell's visit will be to preserve this favorable status quo by convincing Turkish Prime Minister Recep Tayyip Erdogan that the United States will not allow the Kurdish areas to separate from Iraq and that it will protect Turkish interests in the oil center of Kirkuk. Mr. Erdogan could then agree not to dispatch troops across the border without U.S. agreement. Extensive negotiations have so far failed to produce a stable understanding on these points. Mr. Powell would also like greater Turkish cooperation in humanitarian aid to Northern Iraq as well as the U.S. troops now positioned there.

Cooperation in northern Iraq in turn could lay the foundation for U.S.-Turkish collaboration in postwar Iraq -- where the United States could very much use the political and material support of a Muslim ally. Turkey's endorsement of a postwar administration will be crucial, as will be its willingness to rapidly reopen its border and trading routes. Provided the Bush administration can deliver on its promise to prevent Kurdish separatism, Turkey will have much to gain from a pacified and stable Iraq that is fully open for business with its neighbors. Support from Mr. Erdogan, whose Islamic-oriented party has broken new ground in Turkish democracy, could in turn help the Bush administration as it seeks to rebuild its standing in the Muslim world.

Turkey will have to face up to other serious problems after the war. Its deeply indebted economy is dependent on loans from the International Monetary Fund and a tough accompanying stabilization program, while its relations with the European Union are at least as troubled as those with the United States. Ankara's failure to induce Turkish leaders in Cyprus to accept a U.N. plan to end the island's 30-year-old conflict has perpetuated another thorny diplomatic problem. In all these areas Mr. Erdogan could use U.S. help, and provided he continues to work with the Bush administration in Iraq, he should get it. Assuming Mr. Powell's visit goes smoothly, Congress ought to resist the temptation to cut or condition the $1 billion in aid to Turkey included in the supplemental war appropriation. Enough damage has been done to U.S. relations with this strategic country; now is the time to begin rebuilding.