The planned training exercise this year on violent southern Jolo island prompted controversy after Washington said American troops would be allowed to fight the Muslim extremist group Abu Sayyaf despite a Philippine ban on foreign troops participating in local combat. 

Defense Secretary Angelo Reyes left Sunday for Washington to discuss the terms of the training exercise with U.S. defense officials, presidential spokesman Ignacio Bunye said. 

Asked during a radio interview what the government would do if U.S. officials request a combat role on Jolo, Bunye said the Philippine government will turn it down. 

"This is, as of now, hypothetical but if they would request that, we would not allow that because that's against the constitution," Bunye told DZMM radio. 

"I can assure you that because the position of our president is that all these exercises should conform with all our laws, specially our constitution," Bunye said. 

American troops would support Filipino soldiers as trainers and advisers, and the terms of the planned U.S. military presence on Jolo will be disclosed publicly once completed, Bunye said. 

In counterterrorism maneuvers last year on Basilan island, near Jolo, U.S. Special Forces played advisory roles to Filipinos and trained them on night combat and helicopter flying in a crucial help credited for helping wipe out the brutal guerrillas there. 

Reyes said before leaving Manila that Arroyo told him the terms for the planned exercise in Jolo should not violate the constitution and local laws. The proposed exercises would be similar to counterterrorism maneuvers last year on Basilan island, near Jolo, Reyes said. 

U.S. Special Forces played advisory roles to Filipinos who fought the rebels on Basilan. Filipinos then did the fighting and the Americans were allowed only to fire in self-defense, Reyes said. 

U.S. military presence is a sensitive issue in this former American colony, which forbids the presence of foreign troops unless allowed by a treaty. The United States and the Philippines have a Mutual Defense Treaty, and both nations signed a Visiting Forces Agreement in 1998, which allowed the resumption of large-scale war exercises. 

The six-month counterterrorism exercise on Basilan in 2002 set off almost daily protests by left-wing activists and parties outside the U.S. Embassy in Manila. 

Washington's announcement last week about a combat role for Americans in the Philippines set off political turmoil, with opposition lawmakers threatening to take action against Arroyo or Reyes if they were found to have secretly forged an illegal arrangement with Washington. 

The confusion was partly exacerbated by Arroyo's failure to categorically deny Washington's announcement. Arroyo said last year that she believed a combat role for U.S. troops in the Philippines was legal, but she would not agree to it in deference to Filipino soldiers. 

Washington's opening a new front against terrorism in the southern Philippines would likely trigger criticism about the local military's capability to crush the Abu Sayyaf, which some Filipinos say should be treated as an internal security problem. It would also reinforce criticisms that last year's U.S. efforts failed to wipe out the rebels, many of whom fled from Basilan to Jolo. 

U.S. troops on Sunday started a new counterterrorism training of Filipino soldiers expected to last at least 10 months in an army camp in southern Zamboanga city. The training would be separate from the proposed maneuvers on Jolo, officials said. 

Philippine military officials recently said they had underestimated by nearly one half the number of Abu Sayyaf Muslim extremists, whose campaign of mass kidnappings and killings since 2000 has scared away foreign tourists and investment. 

The Philippine military estimates that 208 Abu Sayyaf guerrillas are on Jolo, with 1,070 allies belonging to a large faction of the Moro National Liberation Front, a Muslim separatist group that abandoned a 1996 peace accord.