"We will vote ... for the government's budget, but there will be some modifications," Mr Bertinotti told Italian state television.
The Communist Refoundation party last week rejected the budget, forcing Mr Prodi to resign. Mr Prodi said earlier that the budget he had presented last Thursday would remain unchanged.
Mr Prodi's Olive Tree coalition appeared to have conceded on one main Communist demand - to introduce a draft law aiming at reducing the working week to 35 hours by 2000. The caretaker prime minister said earlier that his centre-left government was close to a deal and that a full announcement would be made today.
The 1998 budget was widely seen as Italy's ticket to joining a European single currency by its launch date in 1999.