Iranians are voting today to choose a new president from two highly contrasting candidates in the country's closest presidential election since the Islamic revolution of 1979.

Voters are choosing in a run-off between Akbar Hashemi Rafsanjani, a former president and moderate cleric who promises a measure of cultural reform and dialogue with the West, and Mahmoud Ahmadinejad, the populist mayor of Tehran, who promises to campaign against poverty and fight for a return to revolutionary values.

Political analysts are watching the run-off closely, saying both the turnout and the outcome are difficult to predict. Mr Ahmadinejad's strong showing in the first round of voting last week was seen as a surprise. He polled 19.5 per cent of the vote, while Mr Rafsanjani took 21.5 per cent.

More than a third of Iran's voters stayed away from last week's vote after students and liberals called for a boycott because ultimate power in Iran still resides with the unelected supreme leader, Ayatollah Ali Khamenei, and a panel of conservative clerics.

"It is a very close race but I think that I am slightly ahead," said Mr Rafsanjani as he cast his vote, pledging to save the 26-year-old Islamic regime from plunging into"extremism".

Anthony Loyd, correspondent for The Times, said from Tehran that voting was peaceful and the city quiet, although most people only come out to vote at the end of the day when it is cooler.

Loyd said the successful first-round showing of the rigidly conservative Mr Ahmadinejad, who has promised to reverse the social reforms achieved by outgoing President Mohammad Khatami, might encourage liberal voters who stayed away last week to go to the polling stations.

"Remember, nearly 37 per cent of the electorate did not vote last time, and one can assume that most of those were moderate or liberal voters. So one might predict that they will be appalled by the prospect of Ahmadinejad winning the run-off and will come out to vote for Rafsanjani.

"The traditional conservative vote tends to amount to about 15 to 20 per cent in Iran, but it does not get much bigger than that. Rafsanjani has a looser but a broader base of appeal."

Loyd said the voters who supported Mehdi Karubi, a moderate reformer, in the first round could be decisive. Karubi won 18 per cent of the vote on a liberal platform, but he also promised Iranians a weekly wage of $62.

"It's difficult to predict where they are going to go," said Loyd. "A lot of them will have been attracted by the prospect of reform, but Karubi's promise of $62 a week clearly appealed to country's poor - and they provide a lot of support for Ahmadinejad."

The first round last Friday ended with bitter accusations of voter intimidation and other abuses. Election overseers have warned the elite Revolutionary Guards and its vigilante wings - both key Ahmadinejad followers - to stay clear of polling sites in the run-off.

Loyd said that faults in the electoral process in Iran cannot disguise the contrast of the candidates on view today, and the choice they present to Iranians for the future:

"These two candidates represent very different options," said Loyd. "No one can doubt that they represent very different things. One the one hand you have Rafsanjani, who is in favour of cultural reform, and on the other, you have Ahmadinejad, who is in favour of rolling back reform and not negotiating with the West. They are chalk and cheese."

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