Army Apache attack helicopters engaged in fierce clashes with Iraqi forces south of Baghdad on Monday and managed to destroy about 10 Iraqi tanks before cutting off the attack.

Pentagon officials said the Apaches took significant anti-aircraft and ground fire during their initial raids on the Medina armored division of Iraq's Republican Guard.

The Iraqis fired rifles and machine guns, an official said. Many helicopters were hit, though all but one managed to return to base.

One helicopter went down, but the official said it was not known if the cause was hostile fire or unrelated mechanical failure.

The Pentagon said the two-man crew was taken prisoner. The pilots were identified as Chief Warrant Officer Ronald D. Young Jr., 26, of Lithia Springs, Ga., and Chief Warrant Officer David S. Williams, 30, of Orlando, Fla.

Maj. Gen. Stanley McChrystal, the vice chief of operations on the Pentagon's Joint Staff, recounted the Apache attack during a briefing for reporters but did not mention heavy resistance from the Iraqis. He gave the impression the attack went relatively smoothly.

With the Medina Division also coming under attack from Air Force and Navy planes, the conditions are being set to weaken that force and create an opening to attack it directly on the ground, McChrystal said. "All of the pieces are falling in place," he said.

McChrystal described the Medina Division as "one of the most powerful of the Republican Guard divisions. I am sure that it has been degraded significantly in the last 48 hours or so. I couldn't judge its current strength. But it is a linchpin to the consistency of the Republican Guard defense."

McChrystal said U.S. ground troops had not yet engaged Republican Guard units in direct combat, other than the attacks by Apaches. He said the helicopter attacks followed military doctrine -- combining deep strikes with psychological operations and, soon, artillery fire -- to weaken the Medina division before the U.S. 3rd Infantry Division hits it full force.

U.S. officials on Monday repeated warnings that they believe Iraq is more likely to use chemical or biological weapons agaisnt coalition troops the closer they get to Baghdad.

The Iraqi Republican Guard controls the bulk of Iraq's chemical weaponry, most of which can be fired from artillery guns or short-range rocket launchers, according to U.S. officials, who discussed the intelligence information on the condition they not be identified. These weapons can generally hit targets from a few dozen miles or less.

The Apaches are armed with up to 16 anti-tank Hellfire missiles, which are designed to lock onto their targets with radar and can be fired from up to 5 miles away. An Apache also could carry up to 36 2.75-inch air-to-ground rockets and up to 1,200 rounds for its 30mm machine gun.

The helicopter is designed to repel 12.7mm and smaller bullets -- small-arms fire -- and resist hits from up to 23mm rounds. The glass around the pilots' seats is not bulletproof, but the pilots' seats are lined with Kevlar, the material used in body armor.

Pentagon officials, meanwhile, complained bitterly Monday about what they called "deadly deceptions" by Iraqi troops pretending to surrender to U.S. forces and then firing on the Americans.

"They are sending forces out carrying white surrender flags or dressing them as liberated civilians to draw coalition forces into ambushes," said Victoria Clarke, spokeswoman for Defense Secretary Donald H. Rumsfeld. "Both of these actions are among the most serious violations of the laws of war," she said.

McChrystal said U.S. forces would continue to accept Iraqi surrenders.

In two episodes Sunday near An Nasiriyah, Iraqi forces deceived Americans into believing they were surrendering or otherwise welcoming them, U.S. officials said.

The officials said one unit indicated it was giving up, but as Marines approached the Iraqis opened fire, killing nine Americans. U.S. military sources said about 40 were wounded.

"Some liken these acts to terrorism," Clarke said. "Such acts involve the enemy willfully violating the laws of war, while simultaneously taking advantage of the coalition forces' compliance with that law."

Heavy fighting continued Monday in An Nasiryah, which is important because of its bridges across the Euphrates which could be used by advancing troops. Cobra attack helicopter pilots returning from strikes on An Nasiriyah on Monday said Iraqis in civilian clothes as well as in uniform had been firing at their aircraft with small arms.

McChrystal expressed regret about a U.S. bomb that hit a civilian bus near the Syrian border. Five Syrians were killed and 10 wounded in the incident, according to Syria's official news agency.

McChrystal said the weapon fired by an Air Force A-10 attack plane was aimed at a bridge 100 miles from the Syrian border. "A bus came into the pilot's view too late to recall the bomb aimed at the bridge," he said.

Asked about the relatively slow pace of Iraqi surrendering, McChrystal suggested that members of the Fedayeen, Saddam Hussein's most trusted militia, had infiltrated regular Iraqi army units, telling them to "fight or be shot in the back."

He suggested that all phases of the U.S.-British military operation were on track.