Relying on harassing tactics never exhibited during the 1991 Persian Gulf War, the Iraqi military has inflicted heavy damage this week on two of the U.S. Army's most fearsome weapons, the Abrams tank and the Apache Longbow helicopter gunship.

Defense officials and analysts were quick to note that no U.S. troops were killed in the Iraqi attacks that badly damaged about 30 Apache Longbows and disabled two Abrams tanks and a Bradley Fighting Vehicle. Hundreds of Iraqis died, and dozens of Iraqi armored vehicles were destroyed in the process, they noted.

Nonetheless, they were impressed by the Iraqis' adaptive tactics and their willingness to fight -- both of which may have been underestimated by some in the Pentagon on the basis of the Iraqis' performance 12 years ago. At that time, their armor formations were destroyed in the open desert, and tens of thousands of troops surrendered.

"This is not a stupid force," said Anthony H. Cordesman, a former Pentagon official at the Center for Strategic and International Studies who is an expert on the Iraqi military. "It's been studying U.S., Russian, Chinese and Yugoslavian literature on asymmetric warfare for 12 years. The elite units have fought well in the past. And this is not a group of cowards."

The Abrams tanks and the Bradley fighting vehicle were disabled Tuesday after Iraqi soldiers repeatedly fired upon the 7th Cavalry Regiment's 500-vehicle convoy moving north as part of the 3rd Infantry Division's advance on Baghdad.

Taking advantage of sandstorms that grounded Apache attack helicopters that would otherwise have provided air cover for the convoy, Iraqi forces believed to be a Republican Guard commando battalion repeatedly attacked with mortars, rocket-propelled grenades, machine guns and small-arms fire. Some of the engagements were hit-and-run. Some involved troops dug in several hundred yards on either side of the road.

During a climactic encounter late Tuesday, the convoy was attacked by hundreds of soldiers. U.S. forces called in airstrikes, and counterattacked and killed most of the attackers.

But when the smoke cleared, two Abrams tanks -- virtually impregnable, 70-ton behemoths -- had been shot in their soft spot, a rear grille covering the engine. Miraculously, the tanks' four-man crews escaped in both cases, a testament to the Abrams's design, which puts a premium on protecting crew members.

"A lot of this is just good war fighting," one retired Army colonel said. "But we haven't encountered it for a long time, and we didn't expect it from the Iraqis. And as they have success, it breeds success."

Some Pentagon officials said yesterday that the attack marked the first time Abrams tanks had been destroyed on the battlefield. An Army official disputed this, saying the tanks "were not blown to bits -- they were rendered immobile. They're going to be evacuated and repaired."

On the battlefield, it was not immediately clear what weapon the Iraqis used to knock out the tanks. A senior defense official said yesterday that it was a French-made Coronet antitank missile.

As the Iraqis demonstrate tactical flexibility and tenacity on the battlefield, foreign technology has become an increasing concern for U.S. commanders. According to the Bush administration, the Iraqis also acquired night-vision goggles, antitank missiles and Global Positioning System jammers this year from three Russian companies.

In attacking a formation of about 40 Apache Longbows on Monday, the Iraqis staged a classic helicopter ambush first perfected by the North Vietnamese in the 1960s. As the lethal, tank-killing aircraft approached on a mission to destroy the Medina Division's dispersed armor, troops dispersed throughout a palm-lined residential area and opened fire with antiaircraft guns, rocket-propelled grenades and a wall of fire from rifles and other small arms.

While the Longbow is equipped with a $3 million millimeter-wave radar that can target tanks and air defenses on the battlefield from five miles away, the $25 million aircraft is most vulnerable to troops who pop out from behind an obstruction as the helicopter is flying low overhead and open fire.

The Iraqi fire was so intense that the Apaches had to break off their mission and return to base. With about 30 helicopters heavily damaged, only one went down in enemy territory. Its two-man crew was unharmed but was taken prisoner.

"Iraqi tactics for using [antiaircraft] guns and short-range defenses reflect a good adaptation of Soviet methods," Cordesman said. "They are evidently using forward spotters to alert troops to oncoming helicopters, and possibly low-flyers like the A-10. The Iraqi [antiaircraft] guns and other automatic weapons then send up a sudden curtain of fire from concealed positions as the helicopters flies into or over the position."

Members of Iraq's Republican Guard often set up their antiaircraft guns in residential neighborhoods.