At least one of the Iraqi vehicles destroyed in the attack was hit by American attack helicopters on the Syrian side of the border, the officials said. They said three of the five Syrian border guards, who exchanged gunfire with American ground forces, remained in American custody for medical treatment.

The American officials refused to say whether there were any fugitive Iraqi leaders in the convoy. They said that as many as 20 Iraqis were detained in the combined air-ground assault, in far western Iraq near the village of Qaim, but they would not provide any details about their identities. A senior Defense Department official said most had been released after it was determined that they did not pose a threat.

The fact that the Pentagon would authorize an attack along the Syrian border and use ground troops underscored the risky nature of the clandestine air-ground attack. It was carried out by Task Force 20, a secret military team, as well as American helicopters and AC-130 gunships with support from Predator drone aircraft, the officials said.

Several senior American officials said they now had no reason to believe that Saddam Hussein or his sons were among the Iraqis killed in the strike. The officials said the possibility that Mr. Hussein or his sons, Uday and Qusay, were traveling in the convoy had been understood to be slim from the outset. With no conclusive evidence found in the five days since the attack, the officials said, they had all but ruled out the possibility that any of the three had been killed.

United States intelligence agencies now also believe that Mr. Hussein and at least one of his sons probably escaped at least two earlier American attacks, on March 19 and April 7.

The White House and the Pentagon provided public confirmation for the first time today of the bare outlines of the raid on Wednesday. But many details remained murky, and a State Department official said the United States had not yet discussed the matter with the Syrian government because so much remained unclear, including whether the Syrian guards had been trying to help or hinder the American effort to halt the convoy.

A Bush administration official acknowledged that the wounded Syrians had been recovered by American ground forces on the Syrian side of the border. But the official said it was unclear whether American troops or aircraft had crossed into Syria during the combat operations itself. 

"We're still trying to ascertain the facts of the incident," a State Department official said.

A Pentagon spokesman, Lt. Col. Gary Keck, said today that he did not have information about whether the attack occurred on the Iraqi or Syrian side of the border. 

"There were some Syrian nationals involved in the incident," he said. "We'll work with the Syrian government to determine the disposition of those individuals."

Defense Department officials said the possibility remained that the Iraqis killed in the attack would be tested to determine whether their DNA matched that of Mr. Hussein or his sons.

The officials said the attack had been prompted by solid intelligence indicating that the convoy, traveling in the vicinity of Qaim, was carrying senior members of the Iraqi leadership. They said that information was of particular interest because of information provided by captured Iraqi leaders, who said that Mr. Hussein and his sons had survived the American-led war and that they might be traveling near the Iraqi-Syrian border, administration officials said.

While there was never any clear indication that Mr. Hussein or his sons might be traveling in the convoy, administration officials said, the overlapping of intelligence made some officials hopeful. It also explains why the target was elevated to a high priority level that, to military commanders, justified the unusually heavy strike and caused them to alert President Bush in advance.

"I don't think there was a high conviction level going in that it was him," a United States government official said, "but there was a lot of excitement."

They said American Special Forces troops in the Iraqi-Syrian border region had carried out other, smaller raids in recent days as part of the search for Mr. Hussein and his sons.

"We're devoting a lot of manpower and resources to this effort," a senior Defense Department official said.

The detained Iraqi leaders include Abid Hamid Mahmoud al-Tikriti, the top lieutenant to Mr. Hussein, who was arrested by American forces in Iraq last week. Mr. Mahmoud has told American interrogators that he fled to Syria after the war with Mr. Hussein's sons but that all were later expelled by the Syrian authorities, Defense Department officials said. The Syrian government has insisted that it has done nothing to harbor Iraqi fugitives, but the issue remains a source of strain between the Syrian and American governments. 

In April, Bush administration officials threatened penalties against Syria because of allegations that it was harboring fleeing members of Mr. Hussein's deposed government and that it had provided Iraq with military equipment. That pressure led to speculation that Syria might be the next American military target after Iraq, but tensions have eased since a visit on May 3 by Secretary of State Colin L. Powell.

The Syrian president, Bashar al-Assad, has said his government closed its border with Iraq. He cited strong tribal connections between the countries, however, and noted the vast desert areas on either side of the 300-mile border.

Senior United States officials who spoke on condition of anonymity said the Bush administration regarded the possibility that Syria might have provided assistance to Iraqi fugitives as an issue of grave concern.

The administration would provide only general details about the operation. "I can confirm for you there was a military operation against a leadership target or targets, and this should be seen in keeping with the ongoing military effort in Iraq to bring justice to people who we believe are associated with the regime or are leaders of the regime," the White House spokesman, Ari Fleischer, said today.

Defense Department officials said today that they did not know how many vehicles had been included in the convoy or how many Iraqis had been killed in the attack. The officials said an American site exploitation team was trying to collect the remains of the dead. They said they did not know the number of people killed, and would not say how many vehicles were in the convoy.