By Massimiliano Di Giorgio and Steve Scherer
ROME (Reuters) - Italy's Democratic Party (PD) chief Pier Luigi Bersani on Thursday denied an imminent split of his center-left bloc, the largest in parliament, amid increasing criticism of his leadership during a prolonged political stalemate.
The PD is divided over whether to join forces with its center-right rival Prime Minister Silvio Berlusconi, who says a "grand coalition" is the only way to break the political impasse caused by February's inconclusive national vote.
Bersani has repeatedly ruled out an alliance with Berlusconi, an unpalatable figure for many PD voters, but high-ranking party officials increasingly argue that the party must open a dialogue with the 76-year-old media tycoon.
The February 24-25 election gave the center left control of the lower house but not the Senate, where only an alliance with Berlusconi's center right or Beppe Grillo's 5-Star Movement would permit the formation of a government.
The PD chief's attempts to woo the anti-establishment 5-Star Movement failed and he now hopes to be able to form what would in effect be a minority government tolerated by rival parties.
The strategy has come under criticism, however, with Rosy Bindi, the party president, telling the daily La Stampa newspaper on Thursday it would allow Berlusconi to pull the plug on the government whenever he wished.
"We'd be putting ourselves entirely in his hands," she said.
Bersani's main rival in the party, Matteo Renzi, the 38-year-old mayor of Florence who lost a primary last year to lead the center-left in the election, has also criticized his leader's strategy, saying that it is wasting vital time.
"They have to hurry up. I personally have said from day one that it would be better to vote again because when there's no clarity, it's better to do it again," he told La7 television on Thursday. "But if they want to get an agreement between Bersani and Berlusconi, they should get on with it."
The dissent has piled pressure on Bersani, a 61-year-old former industry minister, who has been criticized by many in the party by failing to translate the solid opinion poll lead it enjoyed before the election into success.
On Thursday, he dismissed speculation that the party was on the verge of splitting, telling reporters: "We don't have problems of this kind."
As the stalemate has dragged on, the parties have begun preparing for the next major battle, the election of a new president of the Republic to succeed current head of state Giorgio Napolitano, whose term ends on May 15.
The vote will be vital because with Napolitano's mandate running out, constitutional rules prevent him from dissolving parliament, leaving it to his successor to call new elections if no accord can be found to allow the formation of a government.
Voting by the two houses of parliament as well as by representatives from the regions, will begin on April 18 but may take several days to complete.
Bersani, who met Berlusconi on Tuesday to talk about the presidency, has opened up to talks with the center right to select a new head of state and on Thursday met Berlusconi ally Roberto Maroni, leader of the Northern League party.
Various names have been floated in the press, including former prime ministers Giuliano Amato, Romano Prodi and Massimo D'Alema and former European Commissioner Emma Bonino but all have aroused objections and no clear favorite has emerged.
Separately, Grillo's 5-Star Movement (M5S) opened an online vote to allow supporters to nominate candidates for the presidency prior to a vote on the 10 leading names on Monday.
"The Bed and Breakfast couple, Bersani and Berlusconi, are deciding in their secret salons a deal on the president ruling out any form of popular participation, while the M5S is opening an open and democratic process," Grillo said on his blog.
(Additional reporting by James Mackenzie; editing by Michael Roddy)