KIRKUK, Iraq -- Providing money, building materials, and even schematic drawings, Kurdish political parties have repatriated tens of thousands of Kurds into this tense northern oil city and its surrounding villages, operating outside the framework of Iraq's newly ratified constitution and sparking sporadic violence between Kurdish settlers and the Arabs who are a minority here, according to US military officials and Iraqi political leaders.
The rapidly expanding settlements, composed of two-bedroom cinderblock houses whose dimensions are prescribed by the Kurdish parties, are effectively reengineering the demography of northern Iraq, enabling the Kurds to add what ultimately may be hundreds of thousands of voters ahead of a planned 2007 referendum on the status of Kirkuk. The Kurds hope to make the city and its vast oil reserves part of an autonomous Kurdistan.
Kurdish political leaders said the repatriations are designed to correct the policies of ousted President Saddam Hussein, who replaced thousands of Kurds in the region with southern Arabs. The Kurdish parties have seized control of the process, they said, because the Iraqi central government has failed to implement an agreement to return Kurdish residents to their homes.
But US military officials, Western diplomats, and Arab political leaders have warned the parties that the campaign could work to undermine the nascent constitutional process and raise tensions as displaced Kurds settle onto private lands now held by Arabs.
''If you have everyone participating, it'll be a clean affair and you can accomplish your goals," said Lieutenant Colonel Anthony Wickham, the US military's liaison to the Kirkuk provincial government for the past year. ''But don't go behind people's backs, which they have a bad habit of doing," he said, referring to the Kurds. ''Does that bring greater stability to Kirkuk? No. It brings pandemonium."
In late August, Arabs shot and killed a Kurdish agricultural official who was chalking out settlements in Qoshqayah, a disputed village 24 miles north of Kirkuk. An Iraqi soldier was killed and six Arabs were wounded in skirmishes with Kurds before US and Iraqi troops restored order, arresting two dozen Arabs and cordoning off the village. Arab residents said it was the latest of several violent episodes between security forces in the area over the past two years.
''Our patience is about to end," said Sheik Hussein Ali Hamdani, a 64-year-old Sunni Arab tribal leader. ''There are 137 houses in this village now and in each there are at least five" Kurds. ''We will protect our land and not abandon it. It's our honor."
''The Arabs will not give up Kirkuk," said Mohammed Khalil, the leader of an Arab bloc within the Kurdish-dominated Kirkuk provincial council. ''If America really wants to help Iraq, it will try to stop the Kurds from gaining control over Kirkuk, which would start a civil war."
US military officials said they have sought unsuccessfully to persuade Kurdish political leaders to avoid repatriating Kurds onto private lands, a practice they said has inflamed tensions.
Kirkuk, a city of almost 1 million, is home to a combustible mix of multiple ethnicities, a contentious past, and enormous potential wealth. Kirkuk's precise demographic makeup is a source of controversy, but Kurds are believed to represent 35 to 40 percent of the population. The remainder is composed primarily of Arabs, ethnic Turkmen, and a small percentage of Assyrian Christians.
The Kurds, saying they have a historical claim, hope to anchor Kirkuk to Kurdistan, their semiautonomous region. Kirkuk holds strategic as well as symbolic value: The ocean of oil beneath its surface could be used to drive the economy of an independent Kurdistan, the ultimate goal for many Kurds.
''Kirkuk is part of Kurdistan as Washington, D.C. is part of the United States," said Rizgar Ali, president of the Kirkuk provincial council and a top official in the Patriotic Union of Kurdistan, one of the two main Kurdish parties. The other is the Kurdistan Democratic Party.
With the Kurds firmly in control of the provincial government, Kirkuk already shows signs of a remarkable transition. The names of many streets, buildings, schools and villages have been changed from Arabic to Kurdish. Thousands of Kurds who flooded into Kirkuk after Saddam's fall are still living in a soccer stadium, a city jail, and vacant lots. The landscape is replete with gray cinderblocks of the new Kurdish settlements.
The city's fate has been one of the thorniest issues of Iraq's constitutional process.
Under Article 136 of the document ratified by Iraqis on Oct. 15, a referendum on the status of Kirkuk will be held in the province no later than Dec. 31, 2007, but only after the Iraqi government takes measures to repatriate former Kurdish residents and resettle Arabs or compensate them.