By James Mackenzie
ROME (Reuters) - Italian Prime Minister Enrico Letta will seek a confidence vote in parliament on December 11 to confirm his new majority after Silvio Berlusconi's Forza Italia party pulled out of the ruling coalition, the government said.
Letta, who held consultations with President Giorgio Napolitano on Monday, said last week he would seek the confidence vote after his center-left Democratic Party (PD) elects a new leader this coming Sunday and would set out priorities for his government in the coming year.
The decision comes a week after the government comfortably won a confidence vote on the 2014 budget in the Senate by 171 votes to 135, despite Forza Italia formalizing its move to the opposition by voting against the coalition.
Letta survived with the help of a group of center-right rebels, including five government ministers, who broke away from Forza Italia and pledged to support the ruling coalition.
In a formal step to mark the change from the previous coalition, the lower house will vote on the confidence motion on the morning of December 11, followed by a vote in the Senate in the afternoon, the ministry for relations with parliament said.
Although Letta's majority appears solid enough to ensure he wins the vote, he must deal with growing tensions between members of his coalition government, now dominated by his PD.
Matteo Renzi, the ambitious young mayor of Florence who appears set to win the PD party leadership on Sunday, has demanded that the center-left put its stamp more clearly on the coalition, prompting an angry reaction from the center-right.
Formed in the wake of last February's deadlocked election, which left no side able to govern alone, Letta's unwieldy grand coalition of traditional rivals from left and right has struggled to overcome the deep mistrust between partners and has passed few of the institutional reforms it promised.
Following last week's victory in the confidence vote, Letta said his majority was smaller but more compact and effective but the likely election of Renzi as PD leader could yet undermine that cohesion.
The challenge to the government was underlined on Tuesday by comments from European Monetary Affairs Commissioner Olli Rehn, who said Italy was not doing enough to reduce its huge public debt, the second highest in the euro zone. It is set to top 133 percent of gross domestic product this year.
Parliament has still not passed the 2014 budget amid wrangling over such as issues as financing the replacement of a hated housing tax, a key demand of the centre-right, while respecting European Union borrowing limits.
The government must also tackle the intractable issue of reforming a voting system blamed for the stalemate created by the last election.
All sides agree the election law, which makes it difficult for any side to gain a working parliamentary majority, must change, but the parties have failed to agree on an alternative.
(Editing by Gareth Jones)