Washington ? Seeking to repair two of the Bush administration’s most serious diplomatic breaches in the run-up to the Iraq war, Secretary of State Colin Powell will travel to Turkey and Belgium this week to try to head off fresh complications threatening the war effort.

Just weeks after Turkish leaders rebuffed the Bush administration’s request to use their nation as a launching point for a northern assault on Iraq, Powell will be seeking assurances from Turkish officials that they will refrain from sending their troops into northern Iraq. Such a development, Washington has long feared, could trigger clashes with Kurdish forces.

And in Brussels, Powell wants to persuade NATO and European Community leaders — some of them strongly opposed to the U.S.-led war in Iraq — to cooperate with American plans for governing Iraq once the war ends.

After Washington’s failure to win explicit United Nations Security Council endorsement for the Iraq war, a new battle is looming in the council over control of Iraq’s reconstruction, with France threatening to block any U.S. efforts to dominate the process.

Powell’s three-day trip, which begins today, was not previously announced and reflects the urgency of the diplomatic challenges facing the Bush administration as the Iraq war grows more complicated.

The trip also follows complaints by Powell’s critics that his reluctance to travel more in the months before the war contributed to Washington’s inability to assemble a broad coalition to topple Iraqi dictator Saddam Hussein.

“Now that the U.N. work is behind us and some time was freed up, I’m able to travel,” Powell told reporters Monday.

“I want to reassure Turkish leaders that we believe that the work we are doing there now should make it unnecessary for them to consider any incursions in the region,” Powell added.

Turkey, a moderate Muslim democracy and one of Washington’s closest NATO allies, has repeatedly vexed the White House regarding Iraq.

First, the Turkish parliament spurned the Bush administration’s offer of $6 billion in aid in exchange for opening its bases to 62,000 U.S. troops, instead agreeing only to grant the Pentagon permission for overflights.

Military experts say the refusal prevented the Pentagon from opening a northern front against Saddam’s troops and contributed to the military difficulties the U.S. has suffered in the early days of the war.

Then Turkey sent mixed signals over its own intentions in northern Iraq, where Iraqi Kurds have carved out an autonomous government outside of Saddam’s control.

Turkey has long worried that the Iraqi Kurds might try to seize valuable oil fields, declare independence and offer a haven to Turkish Kurds who have waged a sometimes violent separatist struggle against Ankara.

Turkey has several thousand troops in a northern Iraqi buffer zone, but some Turkish officials have invoked the fear of refugee movement from the region and warned that many more Turkish soldiers could be deployed there. There have been no such refugee migrations so far, and Iraqi Kurdish leaders have vowed to fight any Turkish incursion.