Letta is due to outline a programme of priorities in a speech to parliament and is expected to call a confidence vote afterwards.
Italy's President Giorgio Napolitano said Letta would seek "stable commitment for continuing government action from the most immediate deadlines to objectives to be pursued in 2014".
A senior lawmaker in Silvio Berlusconi's People of Freedom party (PDL) said the party should support Prime Minister Enrico Letta in the confidence vote this morning, defying Berlusconi's calls to bring the government down.
"I am ever more convinced that all our party should vote for the government," said Maurizio Lupi, one of the five PDL ministers who resigned from the government on Berlusconi's orders on Saturday.
Lupi's comments echo those of PDL national secretary Angelino Alfano earlier on Tuesday (1 October). Both men are moderates in a party which is deeply divided between so-called hawks and doves. Berlusconi has still not commented on the split in his party.
Napolitano and Berlusconi relations have soured
Silvio Berlusconi said yesterday that Napolitano lacked credibility and was unreliable in failing to safeguard Berlusconi from what he called his persecution at the hands of the judiciary.
Berlusconi's relations with Napolitano have soured steadily since the centre-right leader was convicted in August for tax fraud. His comments on Tuesday, in a letter to a magazine, represent the first time he has criticised the president publicly.
They come as Berlusconi is battling to hold together his PDL party, many of whom are openly dissenting from his decision to try to bring down Enrico Letta's government and push for new elections.
"Enrico Letta and Giorgio Napolitano should have realised that, by not safeguarding the political rights of the leader of the national centre-right, they were destroying an essential element of their credibility," Berlusconi told the weekly Tempi.
"How can anyone be reliable if they ... allow the main government partner to be politically assassinated by judicial means?" he said.
Berlusconi can ill afford to alienate Napolitano, who is the supreme arbiter of Italian politics and is the only person who can dissolve parliament and call new elections, as Berlusconi wants.
Napolitano has made clear his own exasperation with Berlusconi's recent steps to undermine Letta's left-right coalition government.
Last week he described as "absurd" Berlusconi's claims that the judges who convicted him were guilty of subversion or a coup d'etat and repeated that neither he nor Prime Minister Letta could do anything to change the outcome of the trial.