Italian President Giorgio Napolitano, speaking before a parliamentary confidence vote on Wednesday, warned squabbling politicians not to precipitate early elections, saying uncertainty would endanger Italy.

Italy's awkward coalition, patched together from traditional rivals, has been racked by disagreements since Napolitano pushed the centre-left and centre-right parties in April to rule together to end a two-month deadlock after polls in February.

"The president has the duty to warn the country and the political parties of the very serious risks and repercussions...that further destabilisation and uncertainty in the political-institutional framework would bring for Italy," the 88-year-old head of state said in a letter to daily Corriere della Sera.

"I consider the frequent and easy recourse to early elections as one of the most dangerous Italian maladies," he said, referring to the endemic instability that has given Italy 64 governments since World War Two.

Napolitano, who reluctantly agreed to serve a second term as president when the parties could not agree on anybody else, has repeatedly used his power and prestige to defend the government led by centre-left politician Enrico Letta against manoeuvres by party factions.

Wednesday's confidence vote was called to speed up the passage of a package of growth measures and is unlikely to topple the government, but the coalition's stability is threatened by disputes over economic policy and the legal problems of centre-right leader Silvio Berlusconi.

A final verdict due next week in an appeal against the former prime minister's conviction for complicity in tax fraud could bar the billionaire media tycoon from public office, with unpredictable consequences for the government.

Hawks in his centre-right People of Freedom Party are urging him to force an election if he loses the appeal, but Berlusconi has so far urged moderation and caution, saying Italy needs a stable government to face the longest recession since the war.