ROME (Reuters) - Italy's government looked on the verge of collapse on Tuesday after an ally of Prime Minister Romano Prodi deserted the centre-left coalition, depriving him of a parliamentary majority.
Prodi was to address parliament at 10 a.m. (0900 GMT) in a bid to hold the government together, but his chances of survival appeared slim as he was likely to lose any confidence vote in the upper house where he now has fewer seats than the opposition.
"We'll need to see if Prodi will throw in the towel -- something that's anything but certain," said leading daily Corriere della Sera. "(But) the hypothesis that Prodi can emerge intact from such a violent blow seems unbelievable."
Prodi's government has wobbled many times since he narrowly beat his centre-right rival, the media tycoon Silvio Berlusconi, at elections in April 2006.
The latest, possibly fatal, crisis followed the resignation last week of justice minister Clemente Mastella and his decision on Monday to withdraw the support of his small Catholic Udeur party from the coalition. He said he favoured snap elections.
"This majority does not exist anymore, this centre left is finished," said Mastella, whose departure with two other Udeur senators wipes out Prodi's two-seat majority in the upper house.
Mastella quit the cabinet after he and his wife came under investigation in a corruption probe. He initially said his party would vote with Prodi, a position he then unexpectedly reversed.
The defection left Prodi in a corner and prompted opposition calls for him to step down right away.
But the premier chose instead to address lawmakers and possibly coerce his allies into a last-ditch show of support with a confidence vote in both chambers of parliament, something Il Corriere compared to a captain going down with his ship.
"If I go down, I'll do it standing up. I want to look them in the eye as they vote against me," it reported him as saying.
La Stampa daily quoted him saying he believed he would lose a confidence vote -- something which would hand the future of Italy's government to state president Giorgio Napolitano.
"Let's go and see what happens in the Senate. If, as I imagine will happen, we don't have a majority, the ball will be in the court of the head of state."
Napolitano could call fresh elections or ask someone else to form an interim government -- a short-lived administration which could revamp election laws blamed for the political instability.
Such a government would need widespread, cross-party support, which is far from guaranteed. The centre-right former premier Silvio Berlusconi, who believes he has a strong chance of returning to power, is reported to favour a snap election.
Prodi has had a turbulent ride since coming to power in May 2006, after the closest election in modern Italian history.
Weakened by constant infighting in his Catholic-to-communist coalition, he briefly had to resign last year, but no major ally had previously withdrawn support altogether.
Prodi could still win votes in the upper house -- where until now he had a two-seat majority -- with the support of seven unelected lifetime senators as he has done in the past, though their vote cannot be taken for granted.
The prospect of a referendum to change the electoral law, opposed by small parties on both sides of the house because it would reduce their influence in future coalitions, might tip the balance in favour of early elections with the present system.
"For us the crisis is already happening, there's no need to fiddle around," said Natale D'Amico, a senator from a small centrist party in Prodi's coalition that often criticises him.