BAGHDAD, Iraq - With the coalition fraying and guerrilla violence spreading, the latest job for the U.S. military in Iraq appears to be patching holes - like those left by the impending withdrawal of Spanish, Honduran and Dominican troops.

The military here is in the midst of a serious reorganization, shifting and swapping troops to cope with simultaneous crises in the south - where some coalition partners have balked at clashing with rebellious Shiites - and in the west, where a standoff in Fallujah has drained troops from elsewhere.

The rearranging could mean a continued, large U.S. military presence in the south, where the United States had handed security duties to its allies. The coalition partners signed on believing they were patrolling a peaceful region, a situation that has dramatically changed.

The Dominican Republic was the latest planned withdrawal, announcing Tuesday night it would pull its 302 troops out of Iraq within several weeks. Honduran and Domincan forces have been serving under a Spanish-led brigade since August.

Thai Prime Minister Thaksin Shinawatra said Tuesday that his country's 443 troops in Karbala will be withdrawn if the government feels they may be harmed.

"We are giving priority to the safety of the soldiers. If we consider that our soldiers are in danger, that they will be harmed, we will take them back," he said.

The United States has sent other American troops to focus on a threat that intensified during this month's unprecedented violence: the guerrilla attacks on U.S. military supply lines around Baghdad.

The Army has also converted a battalion from the 1st Armored Division into a rapid response force to deal with attacks that are expected to coincide with the June 30 handover of some sovereignty to an Iraqi government, military officials said.

Speaking to U.S. troops massed on the outskirts of the Shiite holy city of Najaf, Army Lt. Gen. Ricardo Sanchez said Iraq has become a "fluid, mobile battlefield." Sanchez, the top U.S. commander, said the military might shift more troops as guerrillas attack.

The Pentagon responded by postponing the return home of more than 20,000 Army troops finishing a year's tour in Iraq and shipping them to the hot zones. They will help replace the 2,000 Spanish, Dominican and Honduran troops in the Najaf region being brought home.

"We'll need to fill that vacuum," said a U.S. official in Baghdad.

The official said some allied troops in the 23-nation multinational force that covers south-central Iraq refused to shoot and kill Iraqi fighters during this month's uprising by a radical Shiite militia, because their rules of engagement forbade it.

On April 7, Ukrainian forces abandoned their base in Kut and pulled out of the city after they came under attack.

Other contributors have sought to avoid a fight from the start. Japan sent more than 600 troops on a non-combat mission of aid and reconstruction in the southern city of Samawa.

South Korea was initially to deploy 3,600 troops in Kirkuk, where ethnic tensions have sometimes turned to violence. But it put that plan on hold, fearing it would lead to combat operations, and is looking at the more peaceable cities of Suleimaniya or Irbil.