DUBAI (Reuters) - Iranian reformists led by former President Mohammad Khatami have endorsed Hassan Rohani, the lone moderate contesting Friday's election for the presidency, held by hardline Mahmoud Ahmadinejad for the past eight years.
Within Iran's complex mix of clerical rulers and elected officials, Supreme Leader Ayatollah Ali Khamenei has the final say on big issues like Tehran's disputed nuclear programme and its support for President Bashar al-Assad in Syria's civil war.
But the next president may at least change the style of Iran's dealings with the world after fiery populist Ahmadinejad steps down in August. He will also be an important adviser to Khamenei and take charge of trying to fix an economy battered by international sanctions, mismanagement and corruption.
One conservative and the only reformist in the race have dropped out in the last two days, leaving four candidates ultra-loyal to Khamenei, one outsider, and Rohani, a moderate cleric.
Khatami, who won two presidential election landslides in 1997 and 2001, threw his weight behind Rohani on Tuesday after Mohammad Reza Aref, the sole reformist candidate approved by Iran's Guardian Council, withdrew on Monday night.
Aref was seen as lacklustre and had little public following.
The reformists' backing of Rohani, a former chief nuclear negotiator known for his conciliatory approach, is an effort to attract the votes of those Iranians hoping for greater freedoms and an end to their country's diplomatic isolation.
A high election turnout, with no repeat of the violent protests that followed the disputed 2009 poll, will be a stamp of legitimacy for the Islamic Republic and its clerical rulers.
"What we have been witnessing ... since 1989 is that the size of the Iranian elite and the size of the popular support for the Islamic Republic has narrowed down significantly," said Mohsen Milani, Iran expert at the University of South Florida.
"There is a large constituency, I would say somewhere between 55 to 65 percent of the electorate that is hungry for reform, hungry for change," he told reporters. "The conservative faction does not have support among this constituency."
Many reform-minded Iranians will still turn out to vote, despite their disappointment at the meagre outcome of Khatami's eight years of cautious reform, and their scepticism after what they believe was Ahmadinejad's rigged re-election in 2009.
"Iranians appreciate that there is a world of difference in politics between bad and worse," wrote Iranian author and journalist Hooman Majd in the Foreign Affairs journal. "Even if they feel like holding their noses as they cast a ballot, they will, in all probability, still go to the polls."
The possibility of popular momentum mounting behind Rohani, just as it appeared to shift behind two reformist candidates in the 2009 election, may spur hardliners to thin their field of candidates to stand a better chance of victory.
Khamenei does not want to take any chances after the embarrassment of the 2009 protests, analysts say, pointing to the exclusion from the race of political heavyweight Akbar Hashemi Rafsanjani and a protégé of Ahmadinejad.
But despite months of talks on the issue, the conservatives have been unable to unite behind a single candidate and Khamenei appears to have not yet intervened to make them do so.
Among the hardliners, chief nuclear negotiator Saeed Jalili appears to be a leading candidate. He has clashed with even his conservative rivals on his uncompromising stance in nuclear talks and would maintain the same policy as president.
Chief among Jalili's hardline critics is Ali Akbar Velayati, a former foreign minister and a close adviser to Khamenei. Former police chief and current mayor of Tehran Mohammad Baqer Qalibaf is the other major contender from the hardline camp.
Editing by Jon Hemming and Alistair Lyon