By James Mackenzie
ROME (Reuters) - Italy's center-left Democratic Party (PD) is expected to elect as its leader the charismatic mayor of Florence, Matteo Renzi, an outsider who promises both a chance of renewal and a threat to Prime Minister Enrico Letta's already fragile coalition.
The 38-year-old Renzi is overwhelming favorite to win Sunday's primary to appoint a new secretary to lead the largest party in Letta's government. But his suspicion of the old-style left, his undisguised ambition and his brusque dismissal of many on his own side has won him as many enemies as friends.
Neither of his rivals, 52 year-old former communist Gianni Cuperlo or the 38-year-old Pippo Civati, a web-literate modernizer, is given any serious chance of winning the primary, which is open to any registered voter, not just party members.
A adept television performer sometimes compared to Britain's Tony Blair, Renzi has already added to the complications facing PD colleague Letta, threatening the delicate balance of his coalition with loud demands for the PD to set its stamp more firmly on the government.
Renzi will not join the government but as party leader he is the favorite to lead the center-left PD into the next election as candidate for prime minister.
Although he has been vague on specifics, he has pushed Letta to move more aggressively on overhauling employment rules to create more jobs, reforming Italy's deadlocked political system and making Europe work better.
"It's now or never," he said this week on one of an endless rounds of television appearances before the primary. "Either the PD seizes this moment or it will be swept away."
Polls give Renzi a higher approval rating than any other politician, with the exception of President Giorgio Napolitano, who stands above the party fray. But he is keenly aware that fortunes can change quickly and his moment may not come again.
He has held back from an explicit pledge of support in a confidence vote on Wednesday that Letta has called to confirm his majority after withdrawal of Berlusconi's Forza Italia. However, his allies dismiss concern that he could be tempted, perhaps by personal ambition, to undermine the government and trigger new elections that could install him as prime minister.
According to a survey by the Tecne polling institute this week, between 1.4 and 2.1 million people are expected to vote in the primary, with Renzi's support seen between 52 and 56 percent, 20 points above his nearest rival, Cuperlo.
Like Blair, Renzi has pledged to drag his party into the modern age, earning himself the label "Il Rottamatore" (the scrapper or demolisher) for his promise to overturn many of the old PD structures and traditions.
But unlike Blair, who remodelled Britain's Labour Party in his own image before winning power, Renzi has not had time to consolidate his hold on the party machinery, a weakness that could cost him heavily when he needs to call in favors.
Letta, a loyal deputy to the last party leader Pierluigi Bersani, is not running in the race and his relations with the quick-talking Renzi are cool at best, despite his insistence that the PD primaries will leave the government stronger.
Following Berlusconi's expulsion from the Senate last month, and the decision by Beppe Grillo, head of the anti-establishment 5-Star Movement not to seek a seat for himself in the last election, Renzi's arrival as PD leader would leave Italy's three most formidable political campaigners all outside parliament.
With Berlusconi and Grillo both in the opposition and free to attack the coalition, Renzi may himself be tempted to distance himself from a government that has struggled to pass meaningful reforms.
Rivals openly accuse him of wanting to provoke new elections to profit from the high tide in opinion polls.
But he faces an unpredictable new challenge following this week's move by the Constitutional Court to reject parts of the current voting law. The ruling would leave Italy with a proportional voting structure that would virtually guarantee short-lived coalitions and worsen the stalemate that has afflicted the system in recent years.
Any Renzi government would be stifled even before it was born. He may prefer to bide his time until 2015, which Letta has set as a target date for the next elections. That would also give time for passing of a new election law.
"I think it's absolutely clear that the government will last at least a year more," a source close to the mayor of Florence said.
He may in any case need to build support within the rest of the party, where many remain suspicious of a young outsider whose political roots owe more to the old center-right Christian Democrat movement than the traditional left.
Outside the party, his message goes down well with a public grown increasingly used to seeing the left floundering as it did in the last election, when it threw away a commanding opinion poll lead and allowed Berlusconi's party back into government.
(Additional reporting by Massimiliano Di Giorgio; editing by Ralph Boulton)