Iraq, June 11 — American forces are carrying out their largest single military operation in Iraq since the end of major fighting, officials said today, with more than 4,000 soldiers surrounding a 30-square-mile area just north of Baghdad said to harbor Baath Party loyalists planning and carrying out attacks on American troops.
Brief gun battles erupted when American forces surrounded this belt of rich green farmland, created by a broad curve in the Tigris River, early Monday, American commanders said. Four Iraqis died, four Americans were wounded and 375 Iraqi men were detained, the Americans said.
Iraqi civilians bitterly complained that the operation was excessive. They said American soldiers handcuffed women and children, beat one man to death and allowed another to die of a heart attack. American officials called the accusations "absolutely false."
The sheer scope of the operation — a pilotless drone, F-15 fighters and AC-130 gunships circled overhead as dozens of armored vehicles and patrol boats cut off escape routes — suggested the seriousness of a new American effort to quell nascent armed resistance in areas north and west of Baghdad dominated by Sunni Muslims.
The area, known as the "Sunni triangle," was a bedrock of support for Saddam Hussein, a Sunni Muslim himself. It has been the center of a recent surge in attacks that have left 10 American soldiers dead and dozens wounded in the last 15 days.
American officials said they had intelligence that senior Baath Party officials were hiding in the area. A released Iraqi detainee said he was asked about Ali Hassan al-Majid, a senior Baath military commander known as "Chemical Ali" for his role in using chemical weapons against the Kurdish minority. American military officials had speculated that he was killed by American bombs in April, but Defense Secretary Donald H. Rumsfeld said last week that he might still be alive.
American officials said a major general and a colonel were detained along with 40 to 50 men believed to be involved in the attacks. The officials said the Army believed that much of the resistance north of Baghdad is supported, financed and coordinated by anti-American elements hiding out in the area.
"There have been a growing number of former regime loyalists, Baath Party officials, fedayeen and Iraqi Intelligence Service type people who exist up there and continue to hire individuals to come in and attack Americans," said Brig. Gen. Daniel A. Hahn, the chief of staff for the V Corps, which oversees Army forces in Iraq.
Col. Frederick Rudesheim, the commander of the operation, which involved soldiers from the Third and Fourth Infantry divisions and paratroopers from the 173rd Airborne Brigade, said senior Baath Party officials, including Mr. Hussein, were not the primary target. He said he had no information corroborating recent reports by Ahmad Chalabi, the Iraqi exile, that Mr. Hussein was alive somewhere north or west of Baghdad and offering $200 to anyone who killed an American.
American officials said their goal was to end attacks by gunmen using techniques such as firing flares, turning on lights in houses and ambushing convoys in remote areas.
The American assessment is that Tikrit, Kirkuk and Baiji, which are farther north of Baghdad, are relatively secure. But the American military command has been concerned about resistance in a swath of territory around the towns of Balad, Taji and Baquba, roughly 30 miles north of Baghdad. Only several hundred Americans have been patrolling them.
Gauging the intensity of the surge in attacks has been difficult. American military officials disclose the deaths of American soldiers in Iraq but do not routinely publicize every attack on American forces. Military officials declined a request this week to produce figures totaling the number of attacks on Americans forces over the last six weeks.
Conversations with soldiers in the area, where the Tigris creates an island of green in a bleak brown desert, suggested that the level of attacks north of Baghdad had been intense.
Soldiers said convoys were routinely fired on in the area at night, with bullets striking the first and last vehicles and rocket propelled grenades whizzing over gunners' heads and between jeeps.
"We are just lucky they are bad shots," said Staff Sgt. John Williams, who was involved in the operation. He said his patrol recently killed 10 armed Iraqis preparing an ambush.
Soldiers said they were now firing back at attackers, and Colonel Rudesheim said there have been no attacks in the two nights since the operation was launched.
But residents complained today that American soldiers broke windows during searches, handcuffed women and children and roughed-up detained men. Relatives of Jassem Rumyad, 52, accused American soldiers of preventing them from giving medication to him before he collapsed and died of a heart attack.
Hella Khalif, Mr. Rumyad's 80-year-old mother, said American soldiers handcuffed and gagged her when she and Mr. Rumyad's wife and daughter shouted that he needed his heart medication. "They put tape over my mouth," she said.
American officials said the account was false and that they allowed the women to give Mr. Rumyad his medication before he suddenly died.
But one American officer said American soldiers in one location handcuffed women and children. The officer said he immediately ordered the handcuffs removed.
A second family accused American soldiers of beating to death Mehedi Ali Jassem, 53, with their rifles and ransacking his house. They showed a mattress that they said was covered with his blood.
American commanders denied the charges and said Mr. Jassem had a cut on his head and his house had been damaged when they arrived to arrest him. They said he stumbled out the door, collapsed and died, apparently of a heart attack.