By DAVID ROHDE and MICHAEL R. GORDON
The New York Times

DHULUIYA, IRAQ – American forces are carrying out their largest single military operation in Iraq since the end of major fighting, officials said on Wednesday. More than 4,000 soldiers are surrounding a 30-square-mile peninsula just north of Baghdad said to harbor Baath Party loyalists planning and carrying out attacks on American troops.

Brief gunbattles erupted when American forces surrounded this peninsula early Monday, American commanders said. Four Iraqis died, four Americans were wounded, and 375 Iraqi men were detained, the Americans said Wednesday.

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 U.S. effort to quell nascent armed resistance in Sunni Muslim-dominated areas north and west of Baghdad.

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 upsurge 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 on the small peninsula. A released Iraqi detainee said he was asked about Ali Hasan 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 speculated he was killed by American bombs in April, but Defense Secretary Donald H. Rumsfeld said last week that he may 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 believes that much of the resistance north of Baghdad is supported, financed and coordinated by anti-American elements hiding out in the peninsula.

"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 Hahn, the chief of staff for the V Corps, which oversees Army forces in Iraq. "So we have done collection and found this peninsula."

Col. Frederick Rudesheim, the commander of the operation that involved soldiers from the 3rd and 4th Infantry divisions and paratroopers from the 173rd Airborne Brigade, said senior Baath Party officials, including Saddam himself, were not the primary target.

American officials said their goal was to end attacks by gunmen using increasingly sophisticated techniques, including firing flares, turning on lights in houses and ambushing convoys in remote areas.