A heavily armored force of 3,000 U.S. troops, followed by 2,000 Iraqi soldiers, police officers, commandos and National Guardsmen, swept into Samarra on Friday to confront insurgents in what a senior Iraqi official said had become an "outlaw city."

The offensive in the city about 65 miles north of Baghdad largely overwhelmed the rebel force during a night and day of occasionally intense fighting. One U.S. soldier was killed, according to military officials, who estimated insurgent fatalities at more than 100. Hospital officials said they had received the bodies of dozens of Iraqis, including women and children, the Reuters news agency reported.

The assault, which began at dusk Thursday, was intended to bring a decisive conclusion to a long-running dispute over who actually runs Samarra, which has a population of 250,000. The police department and city council were co-opted months ago by an insurgency dominated by former members of ousted president Saddam Hussein's government, officials said.

With U.S. armor leading the way for Iraqi forces that secured a sensitive religious shrine and a renowned spiral minaret, the operation was described by Iraqi officials as a model for planned joint operations aimed at putting the interim government in control of several central Iraq cities before national elections promised for January.

"We will spare no effort to clean all Iraqi cities of these criminal gangs," said Qasim Dawood, the government's state minister and national security adviser. "Through these operations, we will open the way not only to reconstruction but also to prepare the general elections to be held as scheduled."

Iraqi and U.S. officials also have vowed to wrest control from insurgents in the Sunni Triangle cities of Fallujah and Ramadi, as well as in Sadr City, the Shiite Muslim slum on Baghdad's east side. Iraq's deputy prime minister promised this week that, after weeks of largely futile efforts to negotiate political settlements, the trouble spots would be the target of military operations during October.

Senior U.S. commanders had privately predicted such operations would come in November or December because of chronic delays in training and equipping new Iraqi troops, who would follow U.S. forces into each city and assert civil order.

But Dawood offered the massive strike on Samarra as evidence of the interim government's determination to move sooner.

"Our forces are in the process of growing," Dawood said at a news conference. "If this week we are not able to do three or four operations in the same time, probably next week or the week after or after a certain time, you may see that we are going to engage many terrorist locations at the same time.

In Fallujah, where news of the military threat was announced from mosques, fighters scrambled to take up defensive positions on the outskirts of the city and plant mines on bridges.

In Samarra, attacks on U.S. patrols have been common. In early July, a car bomb and mortar attack on an Iraqi National Guard station killed five U.S. soldiers and wounded 20. The insurgents, estimated by a U.S. commander to include perhaps three dozen foreign fighters, enforced a strict Islamic code, upbraiding young men for wearing tight jeans and punishing women who eschewed the veil.

Thousands of residents fled Samarra to shelter with relatives in Baghdad and elsewhere. American forces eventually blocked the main bridge over the Tigris River into Samarra, effectively cutting off the city from the country's main north-south highway.

"We recognized some time ago the police chief, the city council and the mayor were ineffective," said Maj. Neal O'Brien, spokesman for the Army's 1st Infantry Division.

Efforts were made to negotiate a political settlement through tribal channels, and on Sept. 9, U.S. and Iraqi forces entered the city to re-seat the city council. But negotiations deteriorated, and on Tuesday, scores of insurgents marched defiantly through central Samarra, some waving the black banner of a group headed by Abu Musab Zarqawi, the Jordanian who has taken credit for many of the car bombings and killings of foreign hostages in Iraq.

The parade was answered by Thursday's offensive. "We call that a target," a senior U.S. military official said the day after the demonstration.

American troops crossing the bridge into the city at 6 p.m. first encountered insurgents unloading ammunition from speedboats on the river below. In the ensuing firefight, four boats were destroyed.

U.S. warplanes and AH-1 Cobra helicopter gunships provided air support as the infantry pushed into the city, skirmishing with insurgents firing assault rifles and rocket-propelled grenades, the military said.

Along the way, 1st Infantry soldiers rescued Yahlin Kaya, a Turk who had been held hostage by insurgents and had been photographed surrounded by masked men in front of a black banner.

The Americans' main military objectives were the city hall and other public buildings that symbolize political control. But Samarra's most famous structures are religious -- and, as such, deemed off-limits to U.S. troops by their commanders.

The green-domed shrine housing the remains of two Shiite imams, Ali Hadi and Hassan Askari, was stormed at midday by commandos of Iraq's 36th Battalion, which had trained to do the same last month at the shrine of Imam Ali in the southern city of Najaf. The Samarra raid caused little damage to the structure but resulted in the capture of about 25 suspected insurgents, the military said.

O'Brien said a unit of special police also secured a second sensitive site, the distinctive spiral minaret that rises above the city's Great Mosque. The tower, known as Malwiyya, dates to 848 and is the symbol of Samarra.

"The important thing to remember is the Iraqi interim government asked us to do this mission," O'Brien said in a telephone interview. "There's more work to do in Samarra," he added, mostly involving restoring order so that reconstruction contracts can go forward, employing local residents and developing a city he said was often neglected by the Hussein government.

Dawood, in turn, emphasized that the Iraqi government was urged into Samarra by its tribal elders and other community leaders -- "responsible people," he said, who gathered in the home of the interim interior minister on Sept. 26.

"Those people represent most of the families and tribes of Samarra," Dawood said. "Most of them expressed concern about the security of the city and the torture and intimidation they suffered from the terrorists. They mentioned it frankly.

"So our answer came as: Here we are."

Qasim Dawood, the state minister and national security adviser for Iraq, said the operation in Samarra, which included thousands of American and Iraqi troops, would aid reconstruction efforts and help prepare for elections.