Since moving into Kirkuk on April 10 behind fleeing Iraqi soldiers, U.S. forces have struggled to build a viable local administration in a region where Kurds are the majority among several often hostile ethnic groups. For help, U.S. officers have turned to eager leaders from the Patriotic Union of Kurdistan (PUK) and the Kurdistan Democratic Party (KDP), who have administered sectors of a largely autonomous U.S.-protected portion of northern Iraq since shortly after the 1991 Persian Gulf War.

The two groups, each with strong militias, have sent in more than 400 police officers and a variety of city administrators from the Kurdish enclave that begins 25 miles east of this city. This has formalized their political reach outside that area for the first time. Many of those police officers are former pesh merga guerrillas, who have spent decades fighting efforts by the government of former president Saddam Hussein to bring the independence-minded Kurds to heel.

U.S. officers have also reached out to local Arabs, Assyrians and Turkmen, ethnic groups that each make up a significant minority of greater Kirkuk's 1 million residents. But Kurds, with a long history of working with the U.S. military, have emerged with more influence in the police force and the interim city council. As a result, the council has already been boycotted by a Turkmen group to protest perceived U.S. favoritism toward Kurds.

The Kurdish parties, among the few well-organized political organizations on Iraq's new landscape, are increasing their visibility here after years of operating as clandestine cells hiding from Hussein's security forces. The PUK has moved part of its interior ministry from the autonomous zone to Kirkuk and has taken over the city's only television station, all with at least tacit U.S. permission.

Party officials have also been buying property from Kirkuk's Arabs, often at inflated prices, in hopes of increasing the number of Kurdish residents before a U.S.-sponsored mayoral and city council election scheduled this week for this city 150 miles north of Baghdad.

"The only real opposition groups in this region were Kurdish, the only ones to stand up to the regime," said Mohammed Kamal Salah, the KDP's deputy director in Kirkuk. "The truth is that this is a Kurdish city, so we have come to represent it."

Until now, U.S. forces have tried to keep the Kurdish parties at arm's length, even ordering the pesh merga out of Kirkuk in the days after the Hussein government's collapse. Turning to them now marks a shift by U.S. forces that has potentially far-reaching implications for stability in a region with restive Kurdish populations scattered across four countries.

While Kurdish party leaders meet in Baghdad to negotiate a role in a federated Iraq, their foot soldiers have worked on the ground to tip the political balance in their favor. The parties, whose pesh merga moved alongside U.S. forces throughout the northern campaign, appear to be riding that mutually useful alliance to greater political power. In endorsing the Kurdish role, however, the United States has become a player in the ethnic realignment that has swept Iraq since Hussein's fall by trying to create local institutions that it hopes will endure after U.S. forces withdraw.

During Hussein's three-decade rule, Iraqi forces put down Kurdish rebellions with massacres and poison gas attacks that killed what human rights groups estimate was more than 100,000 people. After the Gulf War, U.S. warplanes began protecting a 17,000-square-mile Kurdish enclave in northern Iraq. Now the Kurds are trying to extend their reach into the two major northern cities outside that enclave: Kirkuk, which sits above huge oil reserves, and Mosul, an oil center where a similar power struggle between Kurdish, Arab and other ethnic groupings is playing out under the watch of U.S. forces.

Turkey, which did not allow U.S. forces to invade from its territory, has warned against allowing Kurdish groups to assume political or military power in Kirkuk or elsewhere in northern Iraq. Fearing that Kurdish control of the economically important city could encourage Turkey's separatist Kurds, Turkish officials threatened to dispatch troops to evict pesh merga militias after they defied U.S. orders not to enter Kirkuk. The pesh merga withdrew, but the United States has invited their political wing to return.

"It's a reward from the allied forces to allow the Kurds back in here," said Muner Qafi, political director of the Iraqi Turkmen Front, the largest party representing ethnic Turkmen in Kirkuk. "If the Americans left right now, this city would be the start of a huge civil conflict, not only here but across the country."

In recent weeks, U.S. forces have tried to help establish a representative city government and police force. Because Hussein used settlement of Arabs to alter the demographics of this strategic region, census information remained secret. No one is sure of the size of each ethnic group, although most agree that the Kurds represent a majority.

And now the numbers are increasing as hundreds of Kurds -- displaced years ago by Hussein's "Arabization" campaign, which paid Arabs from the south to settle on Kurdish land -- have returned to reclaim their property. Many more intend to do so once school lets out in the Kurdish enclave in July. Violence is already on the rise. On Saturday, witnesses said Arab men from the nearby town of Hawijah arrived in several trucks and opened fire in town, killing at least five people.

Army Col. William Mayville, commander of the 173rd Airborne Brigade, has called on Kurdish leaders to condemn the forced evictions that have sent hundreds of Arabs southward. Until Saturday, he had been mostly successful in preventing deadly ethnic violence and he has asked Kurds to settle property disputes in neighborhood committees. The Kurdish support, however, could change once the Americans leave.

Mayville set up a city council of 24 members, six from each ethnic group. But rival ethnic leaders say the Kurdish influence extends beyond its council seats, given to the two major parties and the Kurdistan Communist Party. The two major Kurdish parties, once bitter political, economic and military enemies within their secessionist movement, have teamed up to consolidate Kurdish political power.

The Iraqi Turkmen Front received all six seats set aside for the ethnic group. But three smaller Turkmen parties complained, and U.S. forces took five seats away from the front to give to the others. Only the Turkmen Front, however, operated in Kirkuk during Hussein's rule. The other three Turkmen parties, Qafi said, were based in the Kurdish enclave and are sympathetic to the Kurdish cause. The Turkmen Front, once referred to as "brothers" by the same Kurdish leaders who now accuse it of being an extremist group with subversive ties to Turkey, will protest by refusing to occupy its seat.

The police force, now consisting of at least 500 officers, has also become dominated by Kurds. Although the precinct commands have been divided evenly, Kurdish officers outnumber those from other groups because they also make up the plainclothes secret police, according to Kirkuk residents and Kurdish rivals. The Assyrian Christians could not fill out the full contingent sought by the U.S. Army, so most of their positions were given to Kurds.

Trained in academies, the Kurdish police have been working for years in the enclave cities of Sulaymaniyah and Irbil. Kurdish officials say all of them are former pesh merga fighters, including Maohat Asad, whose family was driven from its home in Kirkuk by Arabs 16 years ago.

"I came back and found my family house totally flattened," said Asad, who wears a laminated badge issued by the 173rd Airborne Brigade. "Anyone we ever had in our house, even visiting family, we had to tell the Baath Party. They eventually kicked us out. But this will be resolved. Now we're working alongside the Americans."