No candidate received the two-thirds majority required for election, and voting was set to resume on Wednesday, when the necessary majority for victory drops to just over 50 percent, increasing the likelihood of a victor emerging.

Forces loyal to center-left Prodi and to opposition leader Silvio Berlusconi, the outgoing premier, spent Tuesday struggling to reach a consensus on the next head of state, who gives the mandate to form a government.

Prodi and his allies urged the opposition to back their candidate, Giorgio Napolitano, a widely respected senator-for-life and former Communist.

Of the 976 votes cast in the second balloting on Tuesday, 770 were blank, a delaying tactic while the two blocs pursued behind-the-scenes negotiations.

Prodi's coalition has a small majority in the Chamber and a very slender margin in the Senate, meaning that without the opposition's help, it lacked enough votes to garner the two-third majority in the first rounds.

His forces sounded an optimistic note about Wednesday.

"In the end, tomorrow we will elect Napolitano as president of the republic and some of them will vote for him," Massimo D'Alema, a former premier and, like Napolitano, a former Communist, predicted about the opposition.

An opposition leader, Pier Ferdinando Casini, with a centrist party, said that the opposition forces would discuss on Wednesday whether they would vote for Napolitano.

Before Tuesday's voting had finished, Berlusconi told reporters that his coalition would cast blank ballots in Wednesday's first round.

Outgoing President Carlo Azeglio Ciampi declined to award the mandate for the next government as his seven-year-term neared its final days, preferring to leave that task to his successor.

Ciampi was elected in 1999 on the first ballot. But 16 rounds of voting and 13 days were necessary to elect his predecessor.