Premier Romano Prodi resigned on Wednesday after losing a parliamentary vote on his government's foreign policy.
The centre-left chief handed in his resignation during a meeting with President Giorgio Napolitano.
The secretary-general of the president's office, Donato Marra, said Napolitano had "reserved his decision" on whether to accept the resignation pending consultations with political leaders.
Political analysts said the president could ask Prodi to verify whether his nine-month-old government holds a parliamentary majority by calling a confidence vote.
Napolitano could also formally accept Prodi's resignation if the outcome of his talks indicate that the government lacks parliamentary support.
Consultations will begin Thursday morning at 10.30.
A spokesman for the main parties in Prodi's nine-way coalition said that the parties were ready to back the premier in a confidence vote.
"We are ready to reconfirm our full support for the Prodi government. The consultations will be useful for clarification enabling (the government) to pass a confidence vote and show that it has the majority to govern," Dario Franceschini of the centrist Daisy party said.
The government failed to make the majority by two votes in the Senate, with 158 senators voting in favour of its foreign policy line, 136 against and 24 abstaining.
The ballot was not a confidence vote and there was no constitutional requirement for Prodi to resign.
But Foreign Minister Massimo D'Alema had said beforehand that the government should quit if it lost the vote as a "constitutional principle".
Chaos broke out in both chambers of parliament after the vote, with the Silvio Berlusconi-led opposition greeting the result with a chorus of "quit, quit, quit".
Berlusconi issued a statement saying that "Prodi must resign immediately for reasons of political, constitutional and ethical consistency".
"The government has been clamorously defeated in parliament... Prodi and D'Alema asked parliament for its support for their foreign policy ideas and decisions and failed to obtain it," the former premier said.
PRODI ALLIES RATTLED BY AFGHANISTAN AND U.S. BASE.
Prodi has upset pacifist and hard-leftist allies in his coalition by refusing to withdraw Italian troops from a peacekeeping mission in Afghanistan, and approving the expansion of a US military base in the northern city of Vicenza.
The premier has a solid majority in the House but holds only one more seat than the opposition in the Senate, where the government had been expecting extra help from a handful of life senators.
But of the seven life senators, former president Francesco Cossiga voted against the government, two abstained including seven-time former premier Giulio Andreotti and another was absent for health reasons.
The premier was also dealt a blow when Senator Franco Turigliatto of the Communist Refoundation Party (PRC), resigned in protest at the government's foreign policy just before the vote. Another leftist senator, Ferdinando Rossi, joined Turigliatto in abstaining.
Given that abstentions in the Senate essentially count as negative votes, the actions of Rossi, Turigliatto and the two life senators were decisive.
D'Alema had urged potential rebels to support the government's foreign policy in a long, pre-vote speech.
"It is time to take responsibility... I say it loud and clear: we cannot tackle the difficult international challenges ahead without the certainty of broad consensus, and we are here to ask for that consensus," said D'Alema, who is also deputy premier.
D'Alema defended Italy's continued presence in Afghanistan, where pacifist allies say the situation has become too dangerous for a peacekeeping mission.
On the Vicenza base issue, the former premier said that revoking the government's green light to its expansion would constitute an "act of hostility".
More than 70,000 people took part in a demonstration in Vicenza last Saturday against the base's expansion, a project which involves doubling its size to accommodate some 5,000 American troops.
D'Alema said the government had asked Washington to take into account the concerns of the local community.
The subsequent vote was on a motion presented by the governing coalition expressing support for D'Alema's speech and approval of its policy lines.
The government has been forced in the past to resort to confidence votes to maintain coalition unity in the Senate on foreign policy issues.
