A plan to send 3,000 U.S. troops to the Philippines to track down Muslim separatist guerrillas was left in limbo Friday after military leaders from both countries failed to find a way to reconcile Philippine law with the prospect of American combat operations in the island nation.

Speaking after talks with his Philippine counterpart, Defense Secretary Donald H. Rumsfeld said both countries remain interested in arranging for expanded U.S. military assistance to Philippine forces combating the Abu Sayyaf rebel group. But he offered no estimate of the size, timing or exact purpose of any U.S. force that might eventually be dispatched.

Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, who appeared beside Rumsfeld at a Pentagon news conference, said the commander of U.S. forces in the Pacific has been asked to prepare other options that would be more in accordance with the Philippine constitution, which prohibits combat activities by foreign troops except in self-defense.

The freezing of the original plan, only a week after a Pentagon spokesman had detailed it to journalists, was an embarrassment for Manila and Washington and a setback for the Bush administration's effort to widen its global war on terrorism. Government sources familiar with weeks of negotiations indicated that Philippine military authorities may have misjudged the extent to which the legal issues could be finessed and led U.S. officials to believe so, too. In any case, both sides clearly had neglected to settle on how to characterize the operation before its disclosure as a done deal last week.

Philippine Defense Secretary Angelo Reyes, at a separate news conference, described the basic problem as essentially "one of definitions and semantics." He said that while his government saw the proposed involvement of U.S. forces as "a training exercise," the Pentagon was compelled to call it a combat operation, since U.S. military exercises are not usually held in hostile, guerrilla-infested areas like the Sulu Archipelago in the southern Philippines, which is being targeted.

Correspondent Ellen Nakashima in Manila contributed to this report.