RASHAD, Iraq - Marauding gangs of armed Kurds attacked Arabs and Turkmens on Saturday, looting homes, hijacking cars and killing and kidnapping in a wave of violence that threatened to escalate into ethnic war in oil-rich northern Iraq.

A dozen armed Arabs defended the entrance to the poor farming village of Rashad, where Kurds kidnapped two Arab villagers earlier in the day. "If they come here again, there will be fighting and a massacre here," warned Hamad Humadi, who said his brother was one of those kidnapped.

The body of a Kurdish looter, hit in the head during a gun battle between Arabs and Kurds, sat slumped over in his red Volkswagen on the roadside.

About 30 miles away in the Kurd-dominated city of Kirkuk, ethnic Turkmens, who are culturally and linguistically linked to Turkey, warned that the Kurdish attacks would lead to fighting. The United States has been urging Turkey, which worries about its own Kurdish minority, to stay out of neighboring Iraq.

"Their actions . . . may lead to many killings because we must defend ourselves," said Fela Qara Alton, a spokesman for the Iraqi Turkmen Front, a coalition of Turkmen political parties that belongs to the Iraqi opposition to Saddam Hussein. Kurds and Turkmens both claim to be in the majority in Kirkuk.

In Mosul, a predominantly Arab city of 2 million with a large and poor Kurdish minority, terrified Arab residents blamed marauding gangs of Kurds for killing Arab civilians at random and robbing their homes at gunpoint. Dozens of people were killed in spiraling Kurdish-Arab violence, most from gunshot wounds, and the city's Republican Hospital was inundated with casualties.

Many Arabs said Saturday's violence was caused mainly by civilian Kurds from outside Mosul, many of whom came into the city dressed as occupying Kurdish soldiers.

Many experts have warned that an end to 24 years of Saddam Hussein's iron-fisted rule could unleash pent-up ethnic frictions that could tear Iraq apart.

Tens of thousands of Kurds were killed or expelled from the Kirkuk area by Saddam's Arab-dominated regime. Their properties were given to Arabs resettled from elsewhere in Iraq, and now their kin are seeking revenge.

The rising ethnic tension could pose a serious challenge to the small number of U.S. troops deployed in Kirkuk and Mosul.

Residents of Arab neighborhoods in Mosul formed impromptu militias. They blocked off their streets, posted armed guards on rooftops, and didn't hesitate to fire warning bursts from their assault rifles.

Neighborhood militias were blamed for several episodes of vigilantism, although a senior Kurdish official, Fadhil Mirani, called the vigilantes "a good idea," given the absence of any law enforcement.

American Green Berets and Kurdish troopers struggled to mount patrols amid looting, shooting and terror in Mosul. More U.S. Special Forces arrived on Saturday, boosting their number to 800. Green Berets planned to set up a quick training program for a new police force.

There was some let-up in the frenzy of looting. Kurdish commanders said they had secured the municipal hydroelectric plant and vast oil installations outside the city.

Still, anarchy continued. Government offices were set ablaze, only a few bakeries dared to open and gunfire could be heard in every neighborhood. U.S. and Kurdish troopers came under fire from snipers, presumably leftover Baath Party stalwarts and Saddam Fedayeen.

American soldiers discovered a large cache of Iraqi weaponry hidden inside a mosque, including armored personnel carriers, heavy machine guns, thousands of rounds of ammunition, and six French-made Roland anti-aircraft missiles.

On the road from Kirkuk to Saddam's hometown of Tikrit, separate groups of Arabs and Kurds attempted to steal two Iraqi Army trucks but were frustrated because they couldn't figure out how to get large anti-aircraft missiles off the trucks.

Some 1,000 U.S. paratroopers of the Army's 173rd Airborne Brigade were brought into Kirkuk, which fell on Thursday. Some of them fanned out to discourage looting and patrolled key locations, setting up a checkpoint to seize weapons.

The deployment of 1,500 police from the Kurd-run city of Sulaimaniyah also helped calm the city on Saturday. Yet sporadic looting, arson, car jackings and robberies persisted, much of it against Turkmens.

Kurdish looters robbed and killed a prominent Turkmen, Nazam Arif, on Friday night, said Alton, the Iraqi Turkmen Front spokesman.

He said that many of the Kurds posed as peshmergas, guerrillas of the Patriotic Union of Kurdistan or the Kurdistan Democratic Party, the main U.S.-backed Kurdish rebel groups that fought for decades against Saddam.

With security tighter in Kirkuk, heavily armed Kurds impersonating peshmergas ranged far from the city on looting expeditions against Arab villages to the south and west, where there was no security.

In the village of Rashad, Ghanim Aziz Salih brandished a Kalashnikov rifle and shouted: "Is this the democracy they are talking about? More shooting and more killing? We want to live in peace. I want to throw this away."

Maurading Kurds in cars, pickup trucks and a bus pushed to within 35 miles of Tikrit, passing through the Hamrin hills, the boundary of Iraqi Kurdistan.

The villagers in Rashad said they armed themselves after being hit for a second day by Kurdish looters who pillaged five pickups, a tractor and several homes.

At one point on the highway, farmers fired on the Kurdish convoy and stopped it.

Word of the convoy's approach prompted an Arab tribal leader to drive out in a battered Chevrolet to meet it while it was stopped.

Saeed Yussef Zak'r Rafaii, the chief of the Sadat tribe, a stately, elderly man wearing a white headdress and a long brown robe, said he wanted to avoid more bloodshed between Arabs and Kurds who were ransacking Arab villages.

"There is no difference between us. Whether we are Kurds or Arabs, we are all Muslims," Saeed told the Kurds. He urged them to go back to Kurd-dominated Kirkuk.

Saeed's hour-long effort paid off. The Kurds turned around and headed back toward Kirkuk, apparently unwilling to risk a confrontation with the Tikrit area Arab tribes.

A leader of the Tai, one of the largest Arab tribes whose several million members are spread through Iraq and Syria, met with U.S. and Kurdish leaders in Mosul on Saturday.

He may have heard that Defense Secretary Donald H. Rumsfeld, speaking in Washington on Friday, had dismissed the anarchy in Iraq as "untidiness."

"We want to cooperate," said the chieftain, Ghazi al Hanash. "We want to get things tidy again."

(Knight Ridder Newspapers correspondent Ken Dilanian with the 173rd Airborne Brigade in Kirkuk contributed to this report.)