Romano Prodi, the embattled Italian Prime Minister, appeared determined last night to face a confidence vote in the senate today despite fast-crumbling support for his coalition.

In a day of high political drama, the fate of Mr Prodi's 20-month-old centre-left coalition appeared sealed when three Liberal senators, led by Lamberto Dini, a former Prime Minister, said that they would not back it in the senate. Mr Prodi had already been deserted by the Christian Democratic UDEUR party, which has three senate seats.

Last night senior ministers insisted that Mr Prodi was determined to battle on. Yesterday he won a confidence vote in the Lower House, where he has a comfortable majority, by 326 votes to 275. But he has only had a majority of one in the senate since being elected, and it will take only a handful of defections to bring down his fragile administration.

At a lunchtime meeting with Mr Prodi, President Napolitano suggested to him that it would be wiser not continue with plans for a confidence vote in the senate since he clearly no longer had a majority. The Prime Minister will meet the head of state again this morning to decide whether to resign rather than face senate defeat.

If Mr Prodi falls, the President has three main options — he can reinstate Mr Prodi by asking him to reform his coalition and seek another vote of confidence, call elections or appoint a caretaker or “technical” government to introduce electoral reforms designed to give Italy a more stable political system.

At a ceremony in parliament marking the 60th anniversary of the 1948 Constitution, President Napolitano said that Italy was living through “a moment of acute crisis and political uncertainty” but could be sure that the democratic principles enshrined by its postwar leaders remained secure.

However, the latest in a series of interminable government crisis comes just when Italy needs stability for economic reforms to reverse decline. The business daily Il Sole 24 Ore said that there was “an abysmal distance separating the Italian political world from the economic reality in the rest of the country”.

Corriere della Sera said although opinion polls suggested that the Centre Right, under the former Prime Minister Silvio Berlusconi, would win new elections by a clear margin, many Italians wanted a caretaker government to reform the electoral system.

Mr Prodi called the confidence votes in the Lower House and the senate on Tuesday to try and save his fragile coalition from collapse. Mr Prodi, 68, a former economics professor and former European Commission President, whose coalition ranges from the Far Left to centrist Catholics, has often relied in the senate on the seven unelected life senators, who are appointed for their services to the nation and tend to support the status quo.

Pierferdinando Casini, a centre-right Christian Democratic leader, called for “a government of national responsibility”. Mr Berlusconi, who is riding high in the opinion polls despite comparable disarray in his centre-right alliance, insisted that Italy should hold new elections.

Mr Prodi survived the loss of a confidence vote on foreign policy a year ago when a handful of Christian Democats from the Centre Right crossed the floor to support him. La Repubblica said that Mr Prodi had “played every last card he possessed” to survive.

The latest crisis unfolded when Clemente Mastella, the Justice Minister, offered his resignation last week after he and his wife, Sandra, were implicated in a corruption inquiry. Mr Prodi at first refused to accept the resignation, but Mr Mastella insisted that he could not carry on. “This centre-left Government is finished,” Mr Mastella said. “There comes a time when a man says enough is enough.”

Initially Mr Mastella said that his party would support Mr Prodi from outside the coalition on a case-by-case basis, but changed his mind on Monday night and said that it would vote against Mr Prodi in a confidence vote.

Yesterday Mr Mastella denied claims by Mr Berlusconi that the UDEUR would now join the Centre Right. Instead, he hinted that he and other Christian Democratic and centrist leaders would form a new political group “in the centre”. The once-powerful Christian Democrats ruled Italy for half a century after the Second World War but fragmented after corruption scandals in the early 1990s. Many Christian Democrats now feel that the time has come to reclaim the centre ground.

Mr Prodi said that he was proud of the record of his Government, which was “putting Italy back on its feet”, had “reacquired credibility abroad” and cut income tax, tackled tax evasion and restored public finances as well as sending military peacekeeping missions overseas.

President Napolitano has repeatedly said that he wants new election rules before permitting an election because the current system of proportional representation awards parliamentary seats to even very small parties, giving rise to unstable coalitions. The Prodi Government has governed with a fragile majority since narrowly winning elections in April 2006 and has had recourse to confidence votes 31 times to push Bills through, including the 2008 budget.

Because of economic decline and industrial unrest, the Government's popularity has plummeted. Polls show that barely 30 per cent of Italians have confidence in the Prime Minister, down from 45 per cent a year ago. One survey last week found 42 per cent undecided, with 55 per cent of the rest backing the Right and 43.5 per cent the Left.

The Centre Right has also been in disarray since losing the 2006 election. Last November Mr Berlusconi's two main allies, Mr Casini and Gianfranco Fini, head of the far-right Alleanza Nazionale, scathingly dismissed an announcement by the Forza Italia leader — noted for his exuberant behaviour and gaffes — that he was launching a new movement called “The People of Liberty” as a “meaningless spectacle”.

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