ROME (Reuters) - A center-right alliance led by Silvio Berlusconi would be the most likely winner if Italians were to vote now under a reform proposal currently before parliament, according to an opinion poll published on Monday.
Italy is attempting to change electoral rules blamed for a succession of weak, unstable governments that have struggled to revive a chronically sluggish economy or cut a public debt of around 130 percent of output.
The survey, conducted by the Ipsos agency for the daily Corriere della Sera, gave the potential center-right coalition 37.9 percent of the vote, above the 37 percent threshold needed to obtain a large winner's bonus of seats and avoid the need for a second round run-off.
The center-left was credited with 36 percent, while the anti-establishment 5-Star Movement got 20.7 percent.
The center-right benefited from a recent decision by the centrist UDC to move back into its camp, having fought last year's election allied to former technocrat Mario Monti's unaligned Civic Choice movement, which has now all but disappeared.
UDC leader Pierferdinando Casini said in an interview with the daily La Repubblica on Saturday that moderate parties, including the UDC, Berlusconi's Forza Italia and the New Center-Right, which broke away from Forza Italia last year, had to join forces against center-left leader Matteo Renzi.
The UDC itself has the support of just 3.1 percent of voters, but they could swing the election in favor of the center-right.
The poll shows that the center-left Democratic Party (PD) is easily Italy's largest, with 33.5 percent, ahead of Berlusconi's Forza Italia, with 23.2 percent, and 5-Star with 20.7 percent.
But while the PD accounts for almost all the support for the center-left, the center-right bloc is bolstered by disparate parties attracting between 2 percent and 6 percent support, ranging from the pro-autonomy Northern League to the far-right Brothers of Italy.
The poll shows that, while the dynamic and media-savvy Renzi has grabbed all the headlines since storming to victory in a primary for the PD leadership in December, he cannot take electoral success for granted.
Casini's decision to switch back to the center-right was panned as an opportunist move by many politicians and commentators, but Berlusconi was quick to distance himself from the criticism.
"I have always hoped for a return of Pierferdinando Casini to the area of the moderates ... His movement can offer a real contribution to a victory of the center-right," he said in a statement on Monday.
Renzi would be expected to be the center-left's candidate for prime minister, but the choice of center-right candidate is far less obvious. Berlusconi is barred from public office after a conviction for tax fraud.
The electoral reform proposal, the result of a deal drawn up last month by Renzi and Berlusconi, aims to favor strong coalitions or parties by setting high thresholds for entry into parliament and giving a solid majority to the winner, with a run-off round if needed to decide the result.
The next election is not due until 2018, but with Prime Minister Enrico Letta's coalition under constant fire from both Renzi and Berlusconi, most commentators expect the vote in 2015 at the latest.
(Reporting by Gavin Jones; Editing by Ruth Pitchford)