Al YUSUFIYA, Iraq, Oct. 9 - House-to-house raids in this dangerous swath of territory about 30 miles south of Baghdad are turning up few men of fighting age, leading American commanders to believe that insurgents are melting away ahead of troops who are trying to bring the area under Iraqi control.
At the same time, intelligence here has been sketchy, leading to nighttime raids on what appear to be no more than frightened farm families. And the rural terrain - irrigation-soaked roads that are either too narrow for armored vehicles or too weak to support their weight - partly negate the Americans' vast technological advantage.
In at least one case, the problem with the Iraqi back roads led to a disastrous eight-hour ordeal in which new armored vehicles called Strykers became mired in an irrigated field as they were chasing an insurgent who had just fired mortar shells at them. The attacker escaped. Overnight Friday, they searched two towns just east of the Euphrates River and found that they had been deserted, virtual ghost towns.
Even when the raids have uncovered weapons, the men who must have put them there have not been found. In one instance, several women said all their husbands had died.
"One thing that's remarkable to note is how the enemy has changed," said Capt. Bart Hensler, who commands a Stryker unit that is taking part in the raids. "We're always trying to stay one step ahead of each other, but unfortunately the enemy has the advantage."
Lt. Col. Buck James, a battalion commander in the Stryker Brigade, said that even though melting into the population was a time-honored guerrilla tactic, it might be hurting the insurgency here. In Iraq's macho culture, he said, the insurgents' unwillingness to put up a fight may end up costing them the support of the people who are shielding them now.
Lt. Gen. Thomas F. Metz, the commander of ground forces in Iraq, said he believed that the problem of tracking down fighting-age men here was "unique to this particular piece of the operation" and not true of Iraq as a whole.
The enduring optimism of many American troops was summed up by Capt. Rob Krauer of the 24th Marine Expeditionary Unit, who emphasized the need to train Iraqis to do the house-to-house operations in the long run. "We can win a war this way," he said.
But the day-to-day frustrations were enunciated by Specialist Anthony Ellis, sweating in the belly of a Stryker as it slipped off the side of a tiny lane and lurched to a stop, its four right tires subsiding into an irrigation ditch. "Our man slips through the cracks again," he said, disappointment in his voice.
The raids are part of an operation involving about 2,500 marines and G.I.'s and a much smaller number of Iraqi soldiers, who are trying to take back what have become "no go" areas - places where the Iraqi government and the American-led forces exercise little control - before national elections in January.
The elusiveness of the insurgents became clear early Wednesday, when a raid netted hundreds of mortar and artillery rounds and rocket-propelled grenades but no people. Soldiers later searched other buildings in the desert area and found a number of women and children. Under questioning, the women said their husbands had all died.
Several officers said drone reconnaissance aircraft had spotted as many as six men in the area just minutes before troops arrived. Colonel James, who said similar episodes had been replayed over and over, said the quick response by the presumed insurgents indicated that they had developed effective surveillance to monitor the Americans.
Just after nightfall Wednesday, another raid raised questions about the effectiveness of American intelligence here. Acting on a tip that a group of farm houses was the site of mortar launchings directed at a nearby power plant, a swarm of marines, soldiers and armored vehicles stormed into the area.
An explosive charge was used to blow open the door of one building when no one answered a knock. The building turned out to be deserted. But in an adjacent structure, the soldiers found a frightened family of eight huddled in one room.
The head of the family, a middle-aged man who said his name was Abd Jassin Hamid, stood in front of the others, who squatted in a corner. But when asked by a reporter in broken Arabic whether there were mujahedeen in the area, Mr. Hamid's son, Adnan, stepped forward and said in English, "No, no, no, no, no."
As the armed American soldiers stood about waiting for an interpreter, Adnan and his father made digging motions, indicating in pantomime that they were only farmers.
In another building a woman and six children squatted outside the front door, watching in apparent shock as the Americans, wearing night-vision goggles, trooped into their house. There was one man inside. He identified himself as Mr. Jassin and nervously showed the Americans around his house. They found one automatic rifle and a magazine of ammunition, which are allowed for personal protection.
Still, Mr. Jassin plaintively offered to explain why he had the weapon. "Ali Baba fil Iraq!" he said, meaning that there were thieves in Iraq, hardly a controvertible assertion, and that he needed the gun for protection.
The Americans indicated that they had found no reason to suspect the farmers of insurgent activity, yet they returned in force the next day to check out some of the other buildings in the complex. The family filed out of yet another house as two well-kept calves grazed in a shady pen.
Again nothing was found, and because no interpreter was available, one of the soldiers, who had a shotgun dangling from a belt outfitted with shotgun shells along with his other weaponry, struggled to find a way to say they were leaving. "All I know is 'shukran,' " he said, turning to his buddies and using the Arabic word for thank you.
It was suggested that he could say, "Ma'a salama," the traditional words for goodbye.
"I can't learn all that stuff," the soldier said, walking away and using a strong expletive.
At 3 p.m. that day, Thursday, the soldiers were at an encampment near the strategic Jurf Kas Sukr Bridge across the Euphrates when two mortar shells exploded, one close enough to make an enormously loud blast. The Strykers set off in pursuit.
The chase began promisingly, with a pickup trucks sighted moving away from the area from which the mortar was thought to have been fired.
"We'll vaporize them," Specialist Ellis said confidently.
The first thing the soldiers were forced to do was to blast a parked, apparently empty, Toyota pickup truck on their route with heavy machine-gun fire on the chance that it contained a bomb. The vehicles sped past and continued the pursuit.
But on a narrow lane, the four right tires of one Stryker vehicle slipped into the irrigation ditch. Then a second Stryker in the convoy slipped in and was stuck as well.
As the sun set over the fields, the vehicles were still stuck, and a wrecker sent to get them out became briefly stuck as well. A second wrecker arrived.
At midnight, long after the local farmers had lost interest in the operation, the last Stryker was yanked out of the mud and the soldiers went back to their camp.