BAGHDAD, Iraq, Oct. 3 - On the groom's last night as a single man, a bachelor party on his front lawn kicked off with song and dance.
"We love you to death, Moktada," a pair of singers crooned in praise of Moktada al-Sadr, the fiery anti-American cleric who, though absent, overshadowed the groom. "We love you as much as there are leaves on a tree."
Out came one of the groom's best friends, waving his arms like a carnival barker. "Those who follow the Americans are dogs," he yelled. "We swear by Moktada that we won't let our machine guns stop!"
Loyalty to the Shiite cleric burns fierce here in northeastern Baghdad, and especially in Sadr City, a vast slum of 2.2 million people, despite frequent American raids and almost nightly airstrikes. The American military has stepped up its campaign to rout the Mahdi Army, Mr. Sadr's militia, on its home turf here, to drive him to the bargaining table. But it is often impossible to distinguish between civilians and fighters.
A reporter, photographer and interpreter with The New York Times recently spent nearly 24 hours being guided through the battleground streets - and even to a guerrilla bachelor party - by one of Mr. Sadr's midlevel aides. It became apparent that the Mahdi Army here is less a discrete military organization than a populist movement that includes everyone from doctors to policemen to tribal sheiks, and whose ranks swell with impoverished men willing to die.
The day began with a drive to the home of the Sadr aide, a slim, balding 35-year-old man who gave his name simply as Muhammad. Donkey carts plied the dusty streets, mounds of trash lined wide avenues and posters of chubby, black-turbaned Mr. Sadr were plastered across every block. Graffiti in English decorated some walls: "Vietnam Street - We'll make your graves in this place."
Muhammad's home was tucked into a narrow alley in the Chewadar neighborhood. A reeking channel of open sewage ran along the street. A boy dashed around with a toy rifle propped on his shoulder like a rocket-propelled grenade launcher. Nearby, other children played soccer in dirt lots, and women in black robes peeked out from their doorways.
The home was typical of many in Sadr City: a two-story ocher building, with an extended family of 35 squeezed into 1,500 square feet. Muhammad's family moved here in 1962 from Amara, a southern city, before his birth. He is the second-oldest of six brothers, many of whom are members of the Mahdi Army.
"If the Americans didn't try entering Sadr City with their tanks, I can guarantee you not a single bullet would be fired," Muhammad said over a lunch of lamb kebab, a framed portrait of Mr. Sadr on the wall behind him. "Everyone here is part of the resistance."
Muhammad and several of his brothers ate lunch sitting on rugs in the bare concrete living room. Later, one of the brothers, Kassim, a Mahdi commander, picked up an AK-47 and disassembled and assembled it in a couple of minutes. "Mahdi Army basics," he said.
"I fought against the Americans twice in Najaf," he said proudly. "The battle in August was very bloody. There were two armies - one had much better technology, and there was no comparison. But we managed to stay for 26 days."
"We're willing to fight, and we won't let the Americans enter this city," he said, staring down the barrel of his rifle. That sentiment is widespread in Sadr City, where American patrols routinely encounter ambushes and roadside bombs.
In the afternoon, Muhammad drove his black sedan to a street that he said had been the target of an American airstrike three days earlier. Dozens of men from the neighborhood walked to one house and pointed out small indentations in flagstones in the outer courtyard. They said the craters had been made by shrapnel.
Looking in the house, Muhammad pointed to a pool of blood in a corner of the living room and to a family portrait on the wall. The parents and their three children were killed in the strike, he said.
"Everybody was asleep after midnight," a neighbor, Ahmed Faisal, 32, said. "The electricity went off, then the plane came after 1 a.m. It was very noisy."
Mr. Faisal emulated the sound of the plane firing, a jackhammer noise made by the cannons of an AC-130 gunship, which the Americans often deploy over Sadr City.
A senior military official said the strikes were not aimed at civilians, but there was no guarantee that civilian casualties could be avoided.
A half-dozen young men along the alley showed off gauze bandages over wounds on their arms and torsos that they said had resulted from the strike. They insisted they were not Mahdi Army fighters. But when asked whether they hoped Mr. Sadr would drive out the Americans, they said in unison, "God willing!"
Mr. Faisal said: "They're attacking people; they're capturing people. I won't stand idle."
Muhammad drove next to Imam Ali Hospital and visited several people whom he and the doctors said had been wounded in the airstrikes, including three women. The policemen here kissed Muhammad on the cheeks, though few other policemen were to be seen in the center of Sadr City. Posters of Mr. Sadr adorned the walls, including one of him with Hassan Nasrallah, secretary general of Hezbollah.
At another hospital, a construction worker screaming on a gurney in the emergency room said he had been wounded in an American attack. Blood streaked his face and clothes.
Muhammad drove to the site of the attack, on a wide street near an American base. A crowd had gathered several hundred feet from an incinerated pickup truck and a blockade of Humvees. When the Iraqis moved closer, American soldiers fired warning shots into the air.
A bystander named Hussein said a team of Mahdi fighters had lobbed mortars at the base, prompting the Americans to fire missiles back. Officials with the First Cavalry Division later said soldiers had fired a howitzer after dozens of mortar rounds had landed in the base.
Muhammad made a call on his cellphone as he drove away. "Three of the men have just been martyred," he said, his voice quavering. "I tried to evacuate them, but I couldn't."
After nightfall, Muhammad and his brothers loaded AK-47's and pistols into two cars and drove to the bachelor party, where they clapped to music and congratulated the groom. They returned home to one of the frequent three-hour blackouts. Neighbors, one of whom was a police captain, dropped in for tea.
"I supported the invasion at first, to get rid of Saddam, but when they put their flag up over the city of Basra, I knew it would turn into an occupation," the captain said, a Glock pistol tucked into his waistband.
At 1 a.m., Kassim, the militia commander, said he was going out to check on the sentries in the neighborhood. Two of the younger brothers escorted the foreign guests to the roof to sleep on thin mattresses. A full moon had risen, and sheep, satellite dishes and sleeping neighbors were visible on other roofs that spread out in every direction.
The sound of propellers from an unseen AC-130 gunship drifted from the sky above, and two fighter jets swooped through the air. Starting at 4:30 a.m., some people in the streets squeezed off rounds from their AK-47's. Those shots were met by a burst from the AC-130, after which the streets fell silent.