A U.S. citizen was among the people killed in the pilotless missile strike on suspected al Qaeda terrorists in Yemen Sunday, administration officials confirmed yesterday, adding a new element to an attack that reflects the evolving nature of the U.S. war on terrorism around the world.

Ahmed Hijazi and five other suspected al Qaeda operatives were killed by a five-foot long Hellfire missile launched from a remote controlled CIA Predator aircraft as they rode in a vehicle 100 miles east of the Yemeni capital, Sanaa.

Hijazi held U.S. citizenship and was also a citizen of an unidentified Middle Eastern country, a senior administration official confirmed. He was not born in the United States, but resided here for an unknown period of time, the official said.

With him in the vehicle, said Yemeni and U.S. government officials, was a senior al Qaeda leader, Abu Ali al-Harithi, who is suspected of masterminding the October 2000 attack on the destroyer USS Cole.

Hijazi's citizenship highlights the different approaches pursued simultaneously by the administration as it wages its war on terror. In some cases since Sept. 11, American citizens have been arrested and afforded traditional legal rights in the criminal justice system. In others, they have been captured and held indefinitely in military brigs as "enemy combatants." Now, at least in Hijazi's case, a citizen has been killed in a covert military action.

What's more, Hijazi was killed in a country considered at peace with the United States, although U.S. officials say the strike was carried out with the approval and cooperation of Yemen's government.

It was unclear whether the CIA operatives who fired the missile knew that an American citizen was among their targets. It also was unclear whether that would have made any difference.

Even in war, the U.S. government affords greater legal protections to U.S. citizens than foreigners and, in peacetime, the CIA is restricted in the kinds of surveillance and operations it can conduct against U.S. citizens at home and abroad.

The administration, working with the authority of a presidential finding that permits covert actions against Osama bin Laden's al Qaeda terrorist network, considered al-Harithi and his traveling party a military target -- "combatants" under international law.

Officials further contend that Sunday's missile strike was an act of self-defense, which is also permitted under the international laws of war, because al-Harithi already had allegedly attacked the United States in October 2000 when he helped blow up the USS Cole, killing 17 sailors.

Administration officials, intelligence operatives and military analysts, frustrated with the slow, torturous pace of locating and capturing individual terrorists in lawless areas of countries such as Yemen, praised the CIA strikes as an innovative way to get the job done.

"This is an extraordinary change of threshold," said one former intelligence operative who praised the tactic as particularly effective.

The CIA strikes are also a reflection, they say, of how slow the U.S. military, even its Special Operations forces, have been to adapt to the ad hoc, ever-changing tactics of smaller and smaller cadres of terrorists now operating without much of a command structure. The CIA, in fact, has become a much more central tactical military tool in the terrorism war than in any previous conflict, largely because it has a much less cumbersome bureaucracy.

The CIA's separate targeting process, which was used in Sunday's Predator strike, is quicker, more fluid and involves fewer decision-makers in its "trigger-pulling" chain of command than even the nimblest military operation, intelligence experts said.

But while the lethality of the CIA Predator attack was considered successful, it also raises a host of new questions about the legality, effectiveness and ethics of using a tactic outwardly akin to assassination. Assassination is banned by a presidential executive order.

"This ought to be a last resort for the United States," said Jeffrey H. Smith, former general counsel at the CIA. The preferable route, he said, would be to capture and try terrorists, and share the evidence of guilt with the world.

"To the extent you do more and more of this, it begins to look like it is policy," Smith said. "It is not clear that that is an effective tool." Israel, for example, has asserted it has targeted individual Palestinians whom it considers combatants. But the tactic has not stopped suicide attacks and other violence; some analysts suggest it has only outraged the Palestinian community and fueled the violence.

After a while, Smith said, such pinpoint targeting of individuals might "suggest that it's acceptable behavior to assassinate people. . . . Assassination as a norm of international conduct exposes American leaders and Americans overseas."

State Department spokesman Richard Boucher said yesterday that the government did not yet have enough information to verify Hijazi's U.S. citizenship but may learn more from Yemeni authorities. Yemeni officials said yesterday that personal documents, weapons and satellite telephones had been found in the burned-out car.

Yemen is bin Laden's ancestral home, and U.S. intelligence officials describe the country as one of the key refuges for al Qaeda operatives pushed out of Afghanistan by the war there. U.S. Special Forces trainers were sent to Yemen after Sept. 11, 2001.

The U.S. military has been preparing more intensive operations in Yemen. But military operations have proven highly risky. In December, an attempt to force militant Islamic tribal forces on the Saudi border to turn over suspected al Qaeda members ended with the deaths of 13 Yemeni soldiers.

A TV image shows a Yemeni man inspecting the remains of the obliterated vehicle in which al Qaeda operatives were said to have been passengers.