U.S. plans to dispatch more than 1,000 combat troops to the Philippines for joint anti-terrorist operations against the Abu Sayyaf rebels have been put on hold.

It was just one week ago that U.S. defense officials announced they had what they considered an agreement with the government of the Philippines to conduct joint operations against Abu Sayyaf rebels in the Sulu archipelago.

Those operations were to get under way in March with some 350 U.S. Special Operations forces joining Philippine troops in an anti-terrorist sweep. An additional 400 American military personnel would provide back-up from Zamboanga with a U.S. Navy amphibious ready group with some 1,000 Marines standing by offshore with ground and air units ready to join in.

But the U.S. announcement stirred a political outcry in the Philippines where officials, citing constitutional concerns, said American forces would only be involved in training and humanitarian projects.

Now, after talks at the Pentagon with the visiting Philippines defense secretary, Donald Rumsfeld says no decisions have been made on the U.S. role.

"Until the details get worked out as to how we can assist them, we can't know either the numbers or the types of forces that will be used," he said.

Mr. Rumsfeld declines to give details on the sudden reversal in U.S. plans. But he tells reporters at the Pentagon the dispute involves more than mere differences in defining such key terms as combat operations, training or exercises.

"I don't know that it's just semantics," Mr. Rumsfeld added. "It is trying to find a formula where we can provide the maximum help in a manner that is consistent with their constitution."

Last year U.S. forces acted as advisors to Philippine anti-terrorist efforts on Basilan Island. But the American mission was considered part of a training program for Philippine troops, not direct participation in combat operations.