By Ross Colvin

BAGHDAD, Nov 4 (Reuters) - Iran has urged Iraq to postpone a divisive referendum to decide the fate of Kirkuk, an ethnically mixed city that sits on giant oil fields, as part of a series of measures Tehran says will stabilise the country.

The plan was presented on Saturday by Foreign Minister Manouchehr Mottaki at a meeting of Iraq's neighbours in Istanbul but was little noticed amid the frantic diplomacy to avert a Turkish incursion into Iraq to hunt down separatist rebels.

Iran's official IRNA news agency said Mottaki proposed a two-year delay for the referendum, due by Dec. 31, which will decide whether the city is incorporated into Iraq's largely autonomous Kurdistan region.

An Iranian official familiar with the plan said Tehran believed Baghdad was already juggling too many divisive political issues, including how to share oil revenues equitably. Kirkuk was seen as one hot potato too many.

Iraqi officials said their delegation listened politely to the Iranian suggestion, part of a package of proposals that also urged Baghdad to begin a withdrawal of foreign troops.

"We accept the advice, but we refuse to let anyone interfere with Iraq's internal affairs," Iraqi government spokesman Ali al-Dabbagh told Reuters from Istanbul.

Iran says the plan was put forward to help bring stability to Iraq -- although Washington accuses Tehran of promoting violence and backing Shi'ite militias.

Iran has a Kurdish minority and, like Turkey, fears that if Iraqi Kurds control Kirkuk and its oil wealth, this could fuel Kurdish separatism.

Kirkuk, an ancient city 250 km (155 miles) north of Baghdad, is claimed by ethnic Kurds, Arabs and Turkish-speaking Turkmen. Kurds see it as their historical capital, but Arabs who moved there as part of Saddam Hussein's Arabisation plan in the 1970s want to stay under the control of the Baghdad government.

Analysts have warned that the dispute over the city's status could trigger an explosion of violence and possibly draw in neighbouring Turkey unless it is carefully handled. The city has witnessed frequent bombings and shootings in recent months.

MAKING IT OFFICIAL

Under the constitution, the referendum is due to be held by the end of the year, but the government has made no preparations, including holding a census.

While everyone agrees it is now too late to hold the referendum by Dec. 31, the government has yet to make an announcement postponing it and setting a new date.

But, asked whether the referendum would be held on time, Dabbagh said: "I don't expect that. Because of the security situation in Kirkuk we have not done a census, which needs to be done before a referendum."

Joost Hiltermann, an Istanbul-based analyst for the International Crisis Group, said a delay may be a good thing.

"The situation in Kirkuk will get explosive only if the referendum is scheduled and all the non-Kurds oppose it, or if the Kurds try to impose their military control over Kirkuk."

He said the Kurds, who also control the presidency and are a key player in Prime Minister Nuri al-Maliki's Shi'ite-dominated government, would insist on a new deadline and visible preparations for a referendum.

"But I don't see that happening," Hiltermann said. "The Americans don't care to do it, the Iraqi government certainly doesn't care to do it. The Kurds can take unilateral steps, but if they do that they would have everybody against them."

Senior Kurdish politician Najat Hasan, from the Kurdistan Democratic Party (KDP), said a delay of a month or two was acceptable, but any longer would be a "gross violation" of the constitution. (Additional reporting by Mussab Al-Khairalla in Istanbul and Wisam Mohammed in Baghdad)

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