FACTBOX: Iran's parliamentary election

(Reuters) - Iran holds a parliamentary election on Friday to the 290-seat assembly that will be watched for pointers on President Mahmoud Ahmadinejad's popularity.

Conservatives are expected to keep control of parliament but analysts say incoming lawmakers may be more critical of the president as different conservative factions and personalities jockey for position ahead of the 2009 presidential vote.

Pro-reform politicians, the staunchest opponents of the president, had sought to capitalize on popular discontent over Ahmadinejad's handling of the economy and surging inflation. But many of them were barred in pre-vote screening.

Following are some facts about Iran's eighth parliamentary election since the 1979 Islamic revolution:

* QUALIFICATION OF CANDIDATES:

-- Candidates were screened by government-run committees and then the Guardian Council, a conservative body of clerics and jurists that checks hopefuls for their commitment to Islam and other criteria.

-- About 4,500 candidates were approved from about 7,600 who applied.

-- Reformists see disqualifications as an attempt by hardliners to keep them out of power. The Council denies bias.

* CAMPAIGNING

-- Iran does not have a tradition of disciplined party membership or detailed party platforms. Three main groups -- two conservative and one pro-reform -- emerged after months of haggling. Some candidates are backed by more than one group.

They are:

-- UNITED FRONT: The biggest conservative group, which includes supporters and critics of Ahmadinejad, is the most pro-government group and is expected to win most seats. Conservatives label themselves "principle-oriented" or "principlist" politicians for their loyalty to the ideals of the Islamic Republic.

-- INCLUSIVE COALITION: This conservative group includes several Ahmadinejad rivals such as Ali Larijani, who quit as chief nuclear negotiator last year citing differences with the president. It also includes supporters of Tehran mayor Mohammed Baqer Qalibaf. Both lost to Ahmadinejad in the 2005 presidential race and may still eye the presidency.

-- COALITION OF REFORMIST GROUPS: The figurehead for this group is former President Mohammad Khatami. Reformists lost control of parliament in 2004 but hopes of a comeback have been dashed by the vetting process, leaving them able to contest only about 30 percent of seats. Reformists back social and political change but, except for a radical wing, support the Islamic Republic's ideals.

-- Although such groups may play a bigger role in cities, in smaller towns and provincial areas the reputation and ability of politicians to make personal contact with voters are key.

* THE VOTE AND THE RESULT

-- There are about 44 million eligible voters, who must be over 18 years, in the country of 70 million people.

-- The authorities will experiment with electronic vote counting this time. But all ballots will also be counted manually so the final result may not be announced for three days, although partial results may appear sooner.

* A NEW PARLIAMENT

-- Parliament does not determine major policy on issues like Iran's disputed nuclear program, oil or foreign policy.

-- Conservatives are set to dominate parliament again but lawmakers may still be more critical of the president as politicians shape up for the 2009 presidential race.

-- The vote is being watched for pointers on Ahmadinejad's chances of re-election but analysts say much may depend on whether he retains the public approval of Supreme Leader Ayatollah Ali Khamenei, Iran's ultimate authority.

(Writing by Edmund Blair)