ROME, Feb 22 (Reuters) - Italians begin voting on Sunday to choose a new government to succeed technocrat Prime Minister Mario Monti, appointed in November 2011 after Silvio Berlusconi resigned at the height of a financial crisis that threatened to break apart the euro zone.
Early exit polls and projections will start to come out soon after polls close at 3 p.m. (1400 GMT) on Monday and an official result is expected later that evening or early on Tuesday.
No opinion polls have been published since Feb. 8 when a pre-election blackout was imposed and it is unclear how public opinion has shifted in the final two weeks of the campaign.
The last polls suggested the centre-left coalition led by Pier Luigi Bersani was around 6 points ahead of the centre-right coalition led by Berlusconi who staged a strong comeback to cut into the left's once-overwhelming lead.
The anti-establishment 5-Star Movement of comic Beppe Grillo was polling around 16 percent, with Monti's centrist coalition trailing on around 14 percent.
For a graphic on the final polls: http://link.reuters.com/zyc85t
HOW THE VOTE WORKS
There are two houses of parliament and a government must have a majority in both to be able to pass legislation. If no coalition gains a majority in both houses, they can try to strike alliances with other parties.
The system in the Lower House is relatively straightforward. The coalition that wins the biggest share of the national vote is assigned an automatic majority of 54 percent or 340 seats in the 630-seat Lower House.
The situation is more complicated in the 315-seat Senate:
- Seats are assigned by separate ballots in each of the 20 regions, which have varying numbers of seats according to size.
- The coalition that wins the most votes in a region gets an automatic 55 percent majority of seats in that region.
- The remaining seats are distributed between the other parties according to the size of their vote. A minimum threshold excludes groups that win less than 8 percent of the vote from holding any Senate seats in the region concerned.
For a graphic on the Senate makeup, click on http://link.reuters.com/suf26t
The election in the Senate is likely to turn on a handful of votes in a few key regions where the result is too close to call.
Italy's economic powerhouse with 49 seats in the Senate, 27 of which will go to the winning coalition. Home of the pro-devolution Northern League, the centre-right's long domination has been threatened by a series of corruption scandals.
Southern region which has long struggled with corruption, organised crime and economic decline. Has 29 seats, of which 16 go to the winning coalition. Former magistrate Antonio Ingroia polling strongly and may take votes from centre-left.
Shock result in 2012 regional election, which saw big gains for Grillo and clear defeat for Berlusconi underlined potential for surprises from protest vote. Long held by centre-right, Sicily is now completely open. Has 25 seats, with 14 for winner.
Northern industrial region where the Northern League has seen its traditional strength undermined by corruption scandals. Has 24 seats, of which 14 go to the winner.
47 million for Lower House, 43 million for Senate (only those over 25 years of age eligible to vote). Some 3 million Italians living abroad in so-called overseas constituencies are also eligible to vote for both Lower House and Senate.
Regional elections will be held at the same time as the parliamentary vote in Lombardy (7.7 million voters), Lazio (4.7 million), Molise (332,000). Counting in these elections begins on Tuesday afternoon.
(Reporting By James Mackenzie; Editing by Stephen Powell)