Retired Air Force Lt. Gen. James Clapper, head of the National Imagery and Mapping Agency, said vehicle traffic photographed by U.S. spy satellites indicated that material and documents related to the arms programs were shipped to Syria.
Other goods probably were sent throughout Iraq in small quantities and documents probably were stashed in the homes of weapons scientists, Gen. Clapper told defense reporters at a breakfast.
Gen. Clapper said he is not surprised that U.S. and allied forces have not found weapons of mass destruction hidden in Iraq because "it's a big place."
"Those below the senior leadership saw what was coming, and I think they went to extraordinary lengths to dispose of the evidence," he said.
Congress is investigating whether U.S. intelligence agencies overstated information indicating that Iraq had hidden its chemical, biological and nuclear weapons. The Bush administration has defended the intelligence agencies on prewar reports that the weapons were there.
Iraqi government officials "below the Saddam Hussein and the sons level saw what was coming and decided the best thing to do was to dispose, destroy and disperse," he said.
Gen. Clapper said he felt strongly that the satellite imagery of Iraq's weapons facilities before the war was "accurate and balanced."
"Based on what we saw prior to the onset of hostilities, we certainly felt there were indications of [weapons of mass destruction] activity," said the retired general and former director of the Defense Intelligence Agency.
Gen. Clapper said the judgment was based on analysis of spy satellite photographs and was not proof of "what was going on inside of buildings."
He also said the Iraqi government carried out operations after the fall of Baghdad in April to cover up the hidden weapons programs. The chaos following might have included both looting and "organized dispersal made to look like looting," he said.
"So by the time that we got to a lot of these facilities, that we had previously identified as suspect facilities, there wasn't that much there to look at," he said.
Valuable documents on Iraq's weapons were destroyed or lost in the chaos, which included burning of major government ministries.
Saddam began dispersing his weapons and sending elements of his chemical, biological and nuclear programs out of the country in the weeks before the war, he said.
The dispersal included moving both weapons and equipment as well as documents. The activity began before the United Nations began arms inspections last fall.
"What we saw with the avoidance of inspections, there was clearly an effort to disperse, bury, conceal certain equipment prior to inspections," Gen. Clapper said.
As for shipping weapons out of Iraq, he said, there is "no question" that people and material were taken to Syria. He said he did not know whether material also was moved to Iran.
Convoys of vehicles, mostly commercial trucks, were spotted going into Syria from Iraq shortly before the start of the war March 19 and during the conflict, he said.