Former Italian Prime Minister Silvio Berlusconi has defiantly vowed to stay at the centre of politics despite his expected expulsion from parliament over a tax fraud conviction.

In a long-awaited television address shortly before a Senate committee is expected to take the first step in expelling him, the media magnate made no mention of previous threats to bring down the left-right coalition government of Prime Minister Enrico Letta because of the conviction.

"I will always be with you, at your side, expelled from parliament or not. It is not the parliamentary seat that makes a leader," the 76-year-old billionaire said.

He called for centre-right voters to rally behind the relaunched Forza Italia party, with which he first stormed into politics in 1994.

The supreme court last month confirmed a four-year jail term, commuted to one year, on Mr Berlusconi for a giant fraud at his Mediaset television empire. He is expected to go into house arrest or do community service for up to a year.

But he rejected suggestions that he should give up his leadership of the centre-right because of his removal from parliament and the restriction of his liberty.

He called for Italians who loved freedom to "wake up, worry, rebel, become indignant, react and make yourself heard".

"The judiciary has transformed itself into a rival state power, capable of influencing the executive," he said.

Mr Berlusconi wants to seize the initiative despite his conviction by replacing his current People of Freedom (PDL) party with Forza Italia to revitalise centre-right voters and appeal to young people.

PDL secretary Angelino Alfano said his leader would make a final decision on the government's survival only after the Senate vote, where Enrico Letta's Democratic Party (PD), says it will support expulsion.

The euro zone's third largest economy is lagging behind many of its peers in climbing out of recession, partly because Mr Letta's government is too divided to pass vital reforms.