ROME (Reuters) - Prime Minister Matteo Renzi proposed a senior judge to be Italy's next president on Thursday in a move which may strain his government's alliance on reforms with opposition rival Silvio Berlusconi.
Though a largely ceremonial figure, the Italian head of state wields important powers at times of political instability, a frequent occurrence in Italy, when the president can dissolve parliament, call elections and pick prime ministers.
The result of a first round of voting by some 1,009 parliamentarians and regional officials got underway on Thursday and the result was expected by around 1400 ET.
A candidate needs a two-thirds majority to win, which looks unlikely to happen now, but from the fourth round -- probably on Saturday -- only a simple majority is required.
Renzi proposed Sergio Mattarella, a constitutional court judge and a former defense minister, as the candidate for his center Democratic Party (PD) at a meeting of his party's electors. They unanimously accepted the candidacy.
Berlusconi said he would not back Mattarella and accused Renzi of breaking their pact on reforms by not proposing a jointly agreed candidate.
Mattarella, whose brother was murdered by the Sicilian Mafia in 1980, would be "capable of guaranteeing Italy seven years of distinguished leadership", Renzi said.
Mattarella's political roots are in Italy's defunct Christian Democrat party and he has never been close to Berlusconi. In 1990 he resigned as education minister in protest over a decree which favored Berlusconi's media empire.
Renzi said he was not willing to select a compromise candidate and his choice of Mattarella could drive a political wedge between the two leaders whose alliance over electoral and constitutional reform has created friction in Renzi's PD.
On paper, Renzi has the numbers to get Mattarella elected from the fourth round, but the voting is conducted by secret ballot and has shades of intrigue reminiscent of the papal conclaves which take place across Rome's Tiber River.
Italy's previous president, Giorgio Napolitano, 89, who resigned this month, used his powers to the full, intervening in 2011 to replace a scandal-weakened Berlusconi with ex-EU commissioner Mario Monti at the height of the euro debt crisis.
Napolitano appointed three unelected premiers in all.
The 40-year-old Renzi, who has been in power for less than a year, has a lot riding on this presidential vote.
Failure to seat Mattarella in the fourth or fifth round would mean his authority over his party is wavering and put the deal on institutional reform with Berlusconi in jeopardy, raising the specter of an early national election.
With newly elected Greek Prime Minister Alexis Tsipras facing tricky negotiations with German-led European partners on renegotiating Greece's debt, a political crisis in Italy would compound uncertainty in the euro zone.
Additional reporting by Giselda Vagnoni, Roberto Landucci and Isla Binnie; Editing by Crispian Balmer and Gareth Jones