* Letta government almost certain to survive confidence vote
* Berlusconi has threatened to move into opposition
* Rising tension ahead of vote to expel Berlusconi from parliament
* Berlusconi calls on senators to postpone vote
By Giuseppe Fonte
ROME, Nov 25 (Reuters) - Italian Prime Minister Enrico Letta's coalition government said on Monday it would call a confidence vote on its 2014 budget, a move that will give the first clear proof of its strength since Silvio Berlusconi's party split this month.
Confidence votes, which limit the scope for time-consuming amendments, are regularly called to speed legislation in Italy and Letta is almost certain to win with the backing of rebels who split from Berlusconi's centre-right party, now rebranded under its original name Forza Italia.
But the motion in the Senate heightens tension ahead of a vote to expel Berlusconi from parliament this week and is likely to cement the split between Forza Italia and Letta's coalition of left and right formed after February's deadlocked elections.
Forza Italia will meet later on Monday to decide its stance on the budget, Berlusconi told a news conference.
He said he was asking a court to overthrow his tax fraud conviction due to what he said was new evidence that exonerated him, and he called on his fellow senators to postpone the vote to expel him from parliament.
Voting to have one of the country's political leaders booted out of the Senate would "bring you shame before your children, your voters and all Italians," Berlusconi said in a letter to senators he read aloud.
"You can't imagine the indignation you feel in the face of a conviction for a crime you haven't committed," he said. He described himself as "an "exemplary citizen who has never evaded taxes, but who has instead paid lots of them".
The 77-year-old billionaire has promised to break with the government and go into open opposition if Letta's centre-left Democratic Party votes for his removal from parliament as promised. Rallies by his supporters are planned in central Rome during the vote.
His threat to pull out of the coalition prompted a party split earlier this month that has left 30 centre-right senators and 27 deputies supporting the government.
If stripped of his Senate seat, Berlusconi would lose immunity from arrest and from being wiretapped by investigators as he faces at least two other criminal probes and appeals a conviction for paying for sex with an underage prostitute.
The budget, a compromise bill worked out after much wrangling between the coalition partners, includes some tax cuts on labour costs but the European Commission has warned the tax and spending plans might not achieve debt reduction targets.
The confidence vote is scheduled for Tuesday but may be delayed. It is just one part of the budget's passage through parliament, which must be completed by the end of the year.
Squabbling between the centre-left and centre-right, torn between Berlusconi's demands for tax cuts and EU pressure for budget rigour, has largely stymied promises to address Italy's recession and pass much needed reforms.
The government has pledged to keep the fiscal deficit inside the European Union's ceiling of 3 percent of gross domestic product but at 133 percent of GDP and rising, Italy's public debt burden is second only to Greece in the euro zone.