Before the war, American intelligence agencies had identified the site in the town of Najaf as a possible part of Iraq's chemical weapons program, the official said, speaking on condition he not be identified. Indications then were that the plant had not been used for banned weapons activities since 1998, the official said.
Preliminary reports from the site indicate that the initial suspicions were true, and it had not been involved in illicit weapons production in the last five years, the official said.
The captures Sunday of the suspected chemical site, a cache of documents and two Iraqi generals thought to have knowledge of weapons of mass destruction raised the possibility that American forces had begun to find the banned weapons they are fighting to remove from Iraq.
President Saddam Hussein and other Iraqi officials say all of Iraq's chemical and biological weapons were destroyed shortly after the 1991 Persian Gulf War, a claim that United Nations weapons inspectors say cannot be verified.
Finding and eliminating Iraq's weapons of mass destruction are major goals of the war, and finding evidence of such weapons would be a boost for President Bush against critics who say U.N. inspections should have been allowed to continue.
Pentagon officials continue to worry that Saddam's forces could use chemical or biological weapons as coalition ground troops advance toward Baghdad. The Iraqi capital is protected by the Republican Guards, the best trained and best equipped troops of Saddam's army, which U.S. officials say are the units with Iraq's weapons of mass destruction.
Defense Secretary Donald H. Rumsfeld said Tuesday that intelligence agencies were hearing "chatter in the system" indicating that Saddam might have approved the use of such weapons.
"But whether it'll happen or not remains to be seen," Rumsfeld said. He and other U.S. officials have urged Iraqi officers not to follow orders to use weapons of mass destruction and vowed that anyone who did would be tracked down after the war and punished as a war criminal.
The biggest worries for U.S. commanders are Iraq's chemical weapons, which include the nerve agents sarin, soman and VX, as well as mustard agent of the type used in World War I.
Most of the chemical weapons are loaded in artillery shells in rockets, which have a range of about 12 miles or less. U.S. troops have protective gear to deal with chemical weapons, as well as detection equipment that can sniff out a cloud of chemical weapons as far as three miles away.