US MOBILE ARMY SURGICAL HOSPITAL 212, Central Iraq, 8 April 2003 — For days, as his infantry unit rode through the outskirts of Baghdad, Pfc. Robert Sciria peered out intently, searching for threats: The fighting position atop a home. The sandbagged gun emplacement at a gas station. The smiling motorist who suddenly poked a rifle barrel out the window.

Sciria spotted them all. But on Sunday, he only saw the man on top of a building when it was too late. “I saw the flash...Pshhhh!’’ said Sciria, recalling the sound of a rocket-propelled grenade barreling in.

US forces are eviscerating Iraq’s regular army, but interviews with wounded US soldiers at the most forward Army surgical hospital in Iraq depict a complex battle against adversaries who wear civilian clothes, store ammunition in schools and appear suddenly on rooftops or in the middle of a crowd.

These Iraqi tactics frustrate US soldiers who are under orders to limit civilian casualties. And it makes them wonder whether the war will have a clear-cut ending.

“When you think about going to war, you think of it as one big firefight...and you’re done,’’ said Sciria, 20, of Buffalo, N.Y. “But it’s totally different. It’s ongoing. Everywhere you go, you’re in a state of defense.’’

Sciria was torn between sympathy and wariness Sunday morning as his 3rd Infantry Division unit cleared roads leading into southern Baghdad of Iraqi soldiers and weapons. Civilians in long robes streamed past on foot, clutching children and belongings, attempting to flee the city.

“At first, they’re really fearful. They quickly put their hands up. We try to be nice,’’ said Sciria.

But suddenly, as Sciria sat guarding an army checkpoint, a blue pickup truck roared up. The men inside looked like friendly civilians. Then they threw open the car doors and heaved rocket launchers onto their shoulders.

“We took ‘em out’’ with machine-gun fire and armor-piercing rounds, Sciria recounted. A short while later, as he drove his Bradley fighting vehicle north in a convoy, a rocket-propelled grenade streaked in and blasted off the armored vehicle’s gun turret. Slivers of hot metal rained into the hole, burning his back. Sciria was momentarily stunned. He couldn’t breathe. Anxious to avoid being a sitting target, he gunned his engine and roared down the road.

After months of training to fight the Iraqi military, Sciria had been wounded by a lone man in civilian dress.

Staff Sgt. Glen McCaskill, an infantry squad leader with the Army’s 101st Airborne Division, said he had discovered 200 boxes of bullets and mortar tubes Saturday in a classroom in Najaf. He said residents had been pointing out arms caches to US forces. “They want somebody to get it out of the schools,’’ he said.

McCaskill, 33, of Clarksville, Tenn., was going to check on another reported arms cache Saturday night when his team came under sniper fire. He said they turned their Humvee around and hit a mine or some unexploded munitions. “There was a real bright flash. I felt like I’d been hit really hard in the knee and elbow,’’ said McCaskill, who suffered shrapnel wounds.

About 30 miles southwest of Baghdad, another soldier with the 101st Airborne was checking a school Saturday when he made a chilling discovery: In a classroom, crude drawings in crayon depicted people clutching dynamite near US tanks.

A short distance away, a firefight broke out. A man in a white robe climbed onto a roof with a white flag. “As soon as he put the white flag on the building, he pulled out an AK. We shot him,’’ Cruz said.

As Cruz’s unit edged around a building, an Iraqi man suddenly appeared and tossed something. “Grenade!’’ yelled a soldier. The troops ran but the device exploded, spewing shrapnel that caught Cruz’s leg and hip.

Sunday, as he rested in a bed at the army mobile surgical clinic, Cruz said, “They pop up and go away. These guys just come out of nowhere.’’