ROME – Italy's Silvio Berlusconi prepared for likely expulsion from parliament on Wednesday via a momentous vote that will rattle but not bring down the government and leave the billionaire tycoon more at risk of arrest.

Berlusconi has asked fellow senators to delay the vote because he claims to have new evidence warranting a judicial review of the criminal conviction for tax fraud that is the basis for his probable ejection.

Berlusconi's loyalists have attempted stalling tactics but the debate planned for 1800 GMT is likely to go ahead as scheduled although it could be a long one.

Thousands of supporters are expected to mass outside his luxury Rome residence from 1300 GMT, while a smaller group of anti-Berlusconi activists will also gather outside the Senate an hour later.

The day promises to be full of heated rhetoric at an economically crucial time for Italy, which is struggling to end its longest post-war recession and just as parliament debates next year's budget.

Prime Minister Enrico Letta has called for a "non-chaotic situation in Italy" and said a division within Berlusconi's ranks "will help stability".

A group of dissidents led by Berlusconi's former protege, Deputy Prime Minister Angelino Alfano, broke away earlier this month to form their own grouping.

Alfano and his supporters have said they will vote against Berlusconi's expulsion but will stay in Letta's left-right coalition even if the ejection goes ahead.

The government will therefore not collapse even though Berlusconi's Forza Italia party announced on Tuesday it was pulling out of the coalition after just six months of uneasy cohabitation with its leftist rivals.

But the coalition will have a much narrower majority in the Senate of around 10 seats and could be vulnerable to sniping from Berlusconi even outside parliament.

"Berlusconi is still extremely powerful, although that power is declining," said James Walston, a professor at the American University in Rome.

"He still has enormous resources, he still has his media, he still has lots of very diehard supporters inside and outside parliament," he said.

Berlusconi has said a vote to expel him from parliament would be an "indelible stain" on Italian democracy.

Voting to expel "would shame you in front of your children, your voters and all Italians," he said in an open letter to senators, in which he told them that the vote is "not about me, but about democracy".

"You would expel from parliament a political leader who has been prime minister several times and who has represented Italy on the international stage," he said.

Even some of Berlusconi's most hardline opponents have voiced doubts about the expulsion vote and the idea of beating the 77-year-old through the courts and parliament instead of at the ballot box.

Still, a large majority of senators is expected to vote in favour of expulsion.

Legal noose tightens

Ejection from the Senate would remove Berlusconi's parliamentary immunity, which offers a series of safeguards against the arrest of lawmakers, and observers say he is concerned about a possible arrest.

Berlusconi's lawyers dismissed the prospect as "absurd" but he told one interviewer that prosecutors in Naples and Milan were "competing to see who gets me first".

Berlusconi is currently appealing convictions for having sex with an underage prostitute, abusing the powers of the prime minister's office and leaking a confidential police wiretap to damage a political rival.

He also faces trial for bribing a leftist senator to join his party's ranks and could come under investigation for paying off young women who attended his raunchy parties to give favourable testimony.

The last two cases have sparked rumours of an imminent arrest, although experts say it is improbable because of his age and the fact that his passport has already been taken away and he is therefore not a flight risk.

Berlusconi's legal woes have had little effect on his popularity among crisis-hit Italians and recent polls indicate his party would get more than 20 percent of the vote if a general election were held now.

Some polls show a centre-right coalition could even win, although Berlusconi himself will not be allowed to take part in the next elections if the Senate approves the expulsion measure as expected.