American officials who spoke on the condition of anonymity because of the secrecy of the raid said the mission had been mounted rapidly over the weekend on orders from the Central Intelligence Agency when the location of the man suspected of leading an insurgent cell, an Iraqi known as Abu Ghadiya, was confirmed. About two dozen American commandos in specially equipped Black Hawk helicopters swooped into the village of Sukkariyah, six miles from the Iraqi border, just before 5 p.m., and fought a brief gun battle with Abu Ghadiya and several members of his cell, the officials said.

It was unclear whether Abu Ghadiya died near his tent on the battlefield or after he was taken into American custody, one senior American official said.

One United States official described Abu Ghadiya as Al Qaeda in Mesopotamia’s “most prominent” smuggler of foreign operatives crossing the Syrian border into Iraq, and in February the Treasury Department named him as one of four major figures in that group living in Syria.

The official said Abu Ghadiya was in his late 20s and came from a family of smugglers in Anbar Province, in western Iraq. He was also suspected of having led an attack in May on a police station in western Iraq that killed 11 Iraqi officers, an American official said.

Spokesmen for the Defense Department and the C.I.A. declined to comment on the attack. On Sunday, an American military official had denied that American military helicopters had played a part in the raid.

Since the Sept. 11 attacks, the United States has attacked terrorism suspects in the ungoverned spaces of countries like Yemen and Somalia. But administration officials said Monday that the strikes in Pakistan and Syria were carried out on the basis of a legal argument that has been refined in recent months to justify strikes by troops and by rockets on militants in countries with which the United States is not at war.

The justification is different from the concept of pre-emption the administration articulated immediately after the Sept. 11 attacks, and which was used as the rationale for the invasion of Iraq. While pre-emption was used to justify attacks against governments and their armies, the self-defense argument would justify attacks on insurgents operating on foreign soil that threatened the forces, allies or interests of the United States.