WASHINGTON - U.S. special forces entered Syria in pursuit of a convoy believed to be carrying former Iraqi regime leaders last week and wounded three Syrian border guards in a firefight, senior defense officials said yesterday.

The clash with the Syrians occurred as U.S. aircraft or commandos on the ground crossed the frontier as they closed in on the convoy. The incursion into Syrian territory underscored the risks the administration is willing to take in its stepped-up hunt for ousted Iraqi President Saddam Hussein and his sons, whom defense officials described as potential targets of the action.

AC-130 gunships, other fixed-wing aircraft and helicopters destroyed the six-vehicle convoy near the Iraqi city of Qaim, a senior defense official said on condition of anonymity. Qaim is a border town in Iraq's western desert.

American scientists will gather DNA "if appropriate" to determine if remains found at the scene of the strike match Saddam's DNA, a second Pentagon official said. The official added that the Defense Department has no details about the fate or identities of Iraqis in the convoy.

Pentagon officials said that five Syrians were being held by U.S. forces and three received medical treatment. U.S. forces plan to turn the Syrians over to their government. The Americans detained about 20 others during the incident, who were later freed, Pentagon officials said.

The assault targeted Iraqi "regime leadership," but the intelligence apparently was unclear on whether Hussein or either of his sons, Odai and Qusai, were in the convoy.

One U.S. official said the CIA was not aware of any information indicating that they were. Most of the information about the strike has come from the Defense Department, which has its own intelligence operation.

"I can confirm for you that there were military operations against [a] leadership target or targets," White House spokesman Ari Fleischer said. "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 in the regime."

Three senior U.S. senators - the first U.S. lawmakers to visit post-war Iraq - said yesterday that it is crucial that the United States learn soon what has become of Hussein and his sons.

"There are Iraqis who believe he's going to return. There are people who are involved in the sabotage we've already reported, as well as attacks on Americans, who feel the war is not over," Sen. Richard Lugar, an Indiana Republican, told ABC News. Lugar was touring Iraq with Sen. Joseph R. Biden Jr., a Delaware Democrat, and Sen Chuck Hagel, a Nebraska Republican.

"He is in his absence, in effect, still able to be intimidating," Biden said of Hussein. President Bush and other U.S. officials have blamed Hussein loyalists for attacks on coalition forces, Iraqi infrastructure and Iraqi civilians since the regime melted away as U.S. forces marched into Baghdad on April 9. The attacks have slowed reconstruction efforts.

But the United States does not want the search for Hussein to widen the conflict. Officials refused today to discuss the implications of the incursion onto Syrian territory, and would give no details about how far troops thrust into Syria, how long they stayed there, or how they got into the firefight.

The administration has rankled Syrian leaders by accusing them of allowing senior Iraqi leaders to pass into Syria along smuggling routes.

A secretive group called Task Force 20 spearheaded the U.S. assault on the convoy. The covert force specializes in tracking and targeting Iraqi officials based on intelligence from the CIA and other sources, defense officials said. Made up mostly of Army soldiers, Task Force 20 has targeted Hussein and others since before the war began, one official said.