In the world of international terrorism, the several hundred Muslim extremists in the Philippines who call themselves Abu Sayyaf constitute a relatively small outfit with a reputation more for local thuggery than global terror.

So why is the Pentagon committing 3,000 Army, Marine and Navy personnel to a new combat operation with the Philippine armed forces to try to quash Abu Sayyaf?

Administration officials and regional specialists offered several answers yesterday.

"First, it looks like a chance to go after low-hanging fruit -- to move against a not very formidable adversary in the war on terrorism," said Derek Mitchell, an Asia specialist at the Center for Strategic and International Studies. "It also is a chance to finish a job begun last year and, by doing so, demonstrate continued commitment and strengthen a critical alliance with the Philippines."

Last year's effort, which involved the dispatch for six months of 1,200 troops who were restricted to noncombat advisory roles, chased Abu Sayyaf off the island of Basilan but left most of the group's leaders at large. This time, Pentagon officials have made clear that U.S. forces are going to the island of Jolo -- Abu Sayyaf's latest stronghold -- ready to fight and to remain for some time, with no preset endpoint.

The expanded, more aggressive mandate granted by the Philippines to U.S. forces presumably contributed to the Bush administration's willingness to reengage. So reportedly did fresh signs of what some U.S. government analysts consider links between Abu Sayyaf, other terrorist groups and Iraq.

Tying Abu Sayyaf convincingly into any major terrorist network has been a challenge for the Bush administration. Evidence cited a year ago of a connection with al Qaeda appeared dated and tenuous.

It included a report that the group received money in the early 1990s from Muhammad Jamal Khalifa, brother-in-law of al Qaeda leader Osama bin Laden, who channeled funds to various militant Islamic groups. Also, Ramzi Ahmed Yousef, mastermind of the 1993 attack on the World Trade Center, was said to have trained some Abu Sayyaf members in explosives.

But whatever its original political aims, Abu Sayyaf had evolved in recent years into essentially a band of criminals who kidnapped, killed and otherwise terrorized Filipinos and Westerners. The broad war on terrorism may have been the official reason cited for last year's U.S. military foray into the Philippines, but a central underlying aim was to rescue Martin and Gracia Burnham, the missionary couple from Kansas kidnapped and held for ransom by Abu Sayyaf for more than a year.

No U.S. hostages are at issue this time. But American officials say an even stronger case exists now for pursuing Abu Sayyaf as a link in international terrorism.

Details remain classified, but published reports have cited ties between Abu Sayyaf and Jemaah Islamiyah, an extremist Islamic group centered in Indonesia. Last week, the Philippines ordered the expulsion of an Iraqi diplomat, Husham Hussein, after a government intelligence report said Hussein had cell phone contact with two Abu Sayyaf rebels before and after the Oct. 2 bombing in the city of Zamboanga that killed a U.S. Special Forces soldier and two Filipinos. The Iraqi embassy in Manila has denied any connections between its staff and Abu Sayyaf.

"We're seeing more connections among all sorts of groups in the region than we had seen or noticed before," said a government official who monitors the area. "People are treating the idea of Abu Sayyaf's involvement more seriously."

In broader terms, the new initiative is regarded by Pentagon officials as a strategic opportunity to reinforce a critical alliance with the Philippines -- an alliance battered a decade ago when U.S. forces pulled out of Clark and Subic bases. The Philippine government affirmed yesterday that it welcomed the joint operation, although potentially problematic differences emerged in how U.S. and Philippine authorities characterized the American participation.

Ignacio Bunye, a spokesman for Philippine President Gloria Macapagal Arroyo, insisted in remarks on government radio that the role of U.S. troops "would be purely training and advisory" and "their other services would involve civic and humanitarian projects." But Pentagon officials reiterated that a government-to-government agreement reached last week allows for U.S. forces to deploy in the field alongside Philippine troops and engage in combat operations.

The contrasting portrayals reflected the political sensitivity of the operation in a country where many remain wary of the return of large numbers of American forces. Under the terms of the new offensive, Philippine forces will have the lead, with U.S. troops assuming a supporting role -- a distinction that should help sidestep a provision in the Philippine constitution prohibiting foreign forces from carrying out unilateral combat missions. Philippine Defense Secretary Angelo Reyes plans to visit the United States next week for meetings with Defense Secretary Donald H. Rumsfeld and other administration officials.

But regional specialists warned yesterday that the Bush administration must remain mindful of how the Philippine public will perceive the conduct of American forces. Last year, U.S. troops generated particular goodwill by coupling their counterterrorism training with such civic actions as building roads and digging wells to promote development.

"Going back in, we're building on the good faith generated by last year's effort," Mitchell said. "That has made us more confident about going even further this time. But we have to be careful. If we overplay our hand, there could be a backlash. We must demonstrate we're a constructive force and can bring stability."