The U.S. Central Command denied Friday that it had underestimated Iraq's fighting ability but acknowledged that battlefield commanders may be seeing a "more precise" reality of resistance than headquarters.

There has been strong resistance by Iraqi paramilitary forces as U.S. troops have moved north from Kuwait toward Baghdad. American forces sought at first to bypass to, known as Saddam's Fedayeen, have changed in and out of uniform, used civilians -- including children -- as human shields and were forcing Iraqi regular troops to fight on threats of death.

"Our enemy always has a vote in how the circumstances go. I don't think that we have necessarily underestimated (the enemy). No one can ever predict how battle will unfold," he said.

The Army's senior ground commander in Iraq, Lt. Gen. William S. Wallace of V Corps, told The New York Times and The Washington Post on Thursday that unexpected tactics by Iraqi fighters and stretched supply lines were slowing down the campaign.

"The enemy we're fighting is a bit different than the one we war-gamed against because of these paramilitary forces. We knew they were here, but we did not know how they would fight," Wallace said.

Brooks acknowledged that those "closer to the line" may have a different view of the situation than Central Command but stressed that "at the operational level, with what we seek to achieve, it remains unchanged."

"It's a different view down on planet Earth, if you will. As you get closer to the line, the more precise the realities are, and we take all this into account from all our commanders throughout the theater before making decisions to proceed," he said.

He gave an update on where U.S. forces were and what they had accomplished overnight: Special Operations aircraft destroyed two paramilitary headquarters in An Nasiriyah, site of ongoing clashes for several days, he said.

He acknowledged troops were farther to the east than Central Command has previously announced, saying the 1st Marine Expeditionary Force had advanced beyond Qal'at Sukkar, about 170 miles southeast of the capital.

He also acknowledged troops weren't necessarily pressing the advance farther but had "consolidated territory gained over the last several days and conducted active security operations to eliminate identified terrorist death squads."

Finally, he said V Corps, which defeated paramilitary attacks north of Najaf, "continues to shape the battlefield for future operations."

Brooks said 12 Ababil-100 missiles had been fired from Iraq to Kuwait since the war started and that all had been intercepted by U.S. Patriot missile batteries. He said coalition aircraft had destroyed a number of launchers and showed a video of one being hit near the central Iraqi town of Karbala.

The Ababil-100 missile is a truck-mounted multiple rocket launch system with a four-round capability. Each rocket fired by the Ababil reportedly carries a warhead capable of dispensing 300 anti-tank bomblets and 25 anti-tank minelets. It is designed to have a range of 81 miles to 87 miles, well below the limit set by the United Nations after the 1991 Gulf War.

Brooks said preliminary orders had been issued to Iraqi forces for the possible use of chemical weapons, but indicated the assessment was based on prewar intelligence and the recent finds of chemical suits, gas masks and other materials against chemical attack.

"We have seen indications through a variety of sources and reporting means that first orders have been given that a certain point chemical weapons may be used," Brooks said.

He said earlier reports suggested there might be "trigger lines" -- points near Baghdad, which if crossed by coalition troops, could prompt chemical attack.

Brooks said forces have discovered evidence suggesting Iraqi troops have moved chemical weapons south from Baghdad.

"I have not seen anything that says an order has been given to fire," Brooks said.

Central Command has previously reported that gas masks, chemical suits and nerve gas antidotes have been found in captured Iraqi position, including a hospital near An Nasiriyah.