ROME (Reuters) - Pier Luigi Bersani, head of Italy's Democratic Party, led his main rival Matteo Renzi in a primary to pick the centre-left candidate in next year's election, early counting indicated on Sunday, setting the stage for a final runoff vote next week.
With almost a third of the vote counted, Bersani had about 44.6 percent, ahead of Renzi, the 37 year-old mayor of Florence, who was campaigning as a moderniser, on 36.5 percent, according to party officials.
Nichi Vendola, the openly gay head of the left-wing Left, Ecology, Freedom party was in third place with 14.6 percent, while the remaining two candidates, Bruno Tabacci and Laura Puppato trailed far behind.
Assuming the result is confirmed, Bersani and Renzi will compete in a runoff round on December 2.
The outcome of the second round will eliminate a major element of uncertainty dogging Italian politics ahead of spring elections to choose a successor to Prime Minister Mario Monti's technocrat government.
The centre-left alliance is well ahead in opinion polls for the parliamentary election, although uncertainty over what electoral system will be used in the ballot means that it is unclear whether it will be able to form a government without seeking allies from centrist parties.
Even so, the winner of the primary will be in pole position to take over Monti's efforts to control strained public finances and tackle a year-long recession.
Support for former Prime Minister Silvio Berlusconi's deeply divided centre-right People of Freedom party (PDL) has crumbled to less than half than it recorded in the last election in 2008.
Berlusconi, who has changed his mind several times over whether or not to run in the election, added to the chaos facing the PDL, saying on Saturday he was again thinking about standing and throwing plans to hold a centre-right primary into doubt.
About 4 million party and non-party voters took part in the centre-left vote, with queues forming at several outdoor polling booths in cities across Italy.
"It's time for a return to serious politics, and as a consequence we can start to resolve the economy," said 57-year-old Vincenzo Donna Maria, after he cast his vote at a station in central Rome.
Both Bersani and Renzi reject the idea, encouraged by international markets, that Monti should return after the vote to continue his economic policies that have so far included unpopular spending cuts, tax rises and labour reform.
Monti, who has said repeatedly he would be ready to serve a second term if needed, kept up a diplomatic silence about his future on Sunday, saying only that he would consider what contribution he could best make.
Protests on Saturday by tens of thousands of students and workers from across the political spectrum highlighted the levels of discontent among Italians grappling with the slump and rising unemployment in the euro zone's third biggest economy.
While the slick and dynamic Renzi, 37, is much more popular across the general population than career politician Bersani, 61, he has less support among traditional PD party supporters.
Further complicating the national political picture is the dramatic rise of the anti-establishment 5-Star Movement, which is now second in opinion polls, and that around half of Italians say they are either undecided or will abstain.
Additional reporting by Silvia Ognibene in Florence and James Mackenzie, Editing by Myra MacDonald