The vote in Iraq on Sunday to elect a 275-member National Assembly is an important test for US President George Bush’s mission to spread democracy through the Middle East.

Even if the elections take place without violence, both the Bush administration and the fledgling Iraqi government will have to face military and diplomatic difficulties afterwards.

The national assembly has to take office, elect a prime minister, form a government and field a police force able to maintain security. Then it must write a constitution that will lead to other elections, either late this year or in 2006.

The United States must think about when it can begin to bring home some of the 150,000 troops now in Iraq and eventually withdraw from the country.

Bush did not mention Iraq in his inaugural speech last Thursday, although he alluded to it, saying: “Our country has accepted obligations that are difficult to fulfil and would be dishonourable to abandon.”

The administration and Iraq’s interim prime minister, Ayad Allawi, have insisted that the election will take place despite the threat of violence and the expectation that a large section of the country’s Sunni Arabs will not vote.

Low turnouts will increase the chance that declared winners will be challenged after the results.

Administration officials have sought to lower expectations, both for the turnout and the outcome. They have emphasised the importance of other steps to be taken later to guide Iraq’s transformation.

John Negroponte, the US ambassador in Baghdad, noted last Sunday on CNN’s “Late Edition” that the election will be Iraq’s first in several decades. “I think there’s a great deal of excitement about its implications for Iraq’s democracy,” he said.

Increasingly, US officials have acknowledged miscalculations about Iraq. While Bush declared on 1 May, 2003, that major combat had ended in Iraq, the US death toll is still climbing.

National security adviser Condoleezza Rice, Bush’s nominee to-be-secretary of state, said: “There were some bad decisions” on Iraq, although she did not say what they were. Vice-president Dick Cheney, one of the most ardent advocates of invading Iraq, said he overestimated the pace of Iraq’s recovery and ability to govern itself.

Nearly 1,400 members of the US military have died since the US-led invasion that began in March 2003.

The US administration is under pressure, even from some Republicans, to detail an exit strategy.

Former Secretary of State James A. Baker III, an architect of the US war with Iraq in 1991, has urged the administration to consider a phased withdrawal of some of the troops to avoid being accused of having an “imperial design” in the region.

The US government has refused to set a deadline and has said a US pullback will depend on how long Iraq’s security force takes to be fully trained and effective.

The US government also faces the possibility – however remote – that Iraq’s newly elected government will kick American troops out sooner.

Michael O’Hanlon, a foreign policy scholar at the Brookings Institution, said the expected low turnout by Iraq’s Sunni Arabs, who ruled Iraq for eight decades, probably would guarantee that few Sunnis would win election to the new parliament. That would increase the anger among Sunnis and build sympathy for the insurgents.

“Maximising Sunni involvement strikes me as a critical aspect to reducing their support for the insurgency,” O’Hanlon said.

Jon Alterman, a Middle East expert and former special assistant secretary of state for Middle East affairs, acknowledged that going ahead with the elections now is not ideal but said putting them off would “give a victory to the people who are trying to derail the process”.

What happens on Sunday will say a great deal about the future of Iraq.