Mr Berlusconi has refused to concede defeat to his rival's centre-left coalition ahead of a recount, but an initial scrutiny of the ongoing review of contested votes suggested late Thursday the result would not be overturned.
The recount was close to a conclusion and the votes were being divided equally between the rival coalitions, the ANSA news agency reported.
Mr Prodi's Union coalition said in a statement that the recount "is demonstrating the validity of the poll result."
Recount demanded
Mr Berlusconi, who initially demanded a recount of 43,000 contested votes after Mr Prodi won, called for a wider check of returns from all 60,000 polling stations, as well as more than one million votes deemed invalid.
"The result must, and will, change because there has been endless vote rigging in different places, all over Italy," said Mr Berlusconi after meeting President Carlo Azeglio Ciampi late Wednesday.
Italian newspapers said the prime minister had hoped to get the Italian president to sign a decree extending the recount to include more than a million spoiled votes, but Mr Ciampi is believed to have refused.
Mr Berlusconi has kept up a barrage of electoral fraud allegations and refused to concede defeat for his centre-right government ever since the results Tuesday showed Mr Prodi as the narrow winner.
But the 69-year-old prime minister appears increasingly isolated after key allies publicly raised doubts over his claims.
"Berlusconi can take our word for it: the Left won so it should govern," said Roberto Maroni of the Northern League. Mr Maroni, welfare minister in the outgoing government, dared the centre-left "to govern if it can. Our aim is to devise means by which to ensure that such a government falls as soon as possible."
Another of the prime minister's allies, Lorenzo Cesa of the Christian
Democrat UDC party, said of the recount: "I don't believe it will change the outcome of the election."
World leaders acknowledge Prodi
Mr Prodi pressed ahead with talks with his coalition partners on forming a government, and sought to give an impression of a smooth transition to power.
He said that after Mr Berlusconi's latest fraud allegations he had made a late-night phone call to Interior Minister Giuseppe Pisanu, whose ministry was responsible for overseeing the vote.
"Relax, and have a good Easter," Mr Prodi said Mr Pisanu had told him. "The situation seems calmer, because I know there's nothing to worry about. We need patience, but in the end, this is democracy," he told journalists.
Meanwhile, Britain, Germany and Brazil joined the growing number of countries acknowledging Prodi's election victory.
Mr Prodi's office said he had received congratulatory phone calls from German Chancellor Angela Merkel, British Prime Minister Tony Blair and Brazil's President Luiz Inacio Lula da Silva.
However, there were none yet from US President George W Bush, an ally of Mr Berlusconi, and Pope Benedict XVI.
Mr Prodi's admission that Italy will have to wait until May for a new government has done little to quell the growing sense of a political crisis.
Economists warned the stalemate would do little to help Mr Prodi's incoming centre-left government to kick-start an ailing economy.
"It's not a good start for the new government," said Bank of America economist Matthew Sharratt.
Raj Badiani, economist with Global Insight, said the standoff would have "no immediate impact" on the economy but could affect recent positive consumer and business confidence figures if allowed to drag on.
The situation is complicated by the fact that Italy's president, whose duty it is to swear in the new government, ends his seven-year term of office on May 18. Mr Ciampi, 85, has said he wants his successor to do the swearing in.