ROME, Dec 12 (Reuters) - Silvio Berlusconi will have to withdraw his bid for a fifth term as Italy's prime minister if he wants to seal a crucial alliance with his former coalition partners in the Northern League, the head of the regionalist party was quoted as saying on Wednesday.
An accord between Berlusconi's People of Freedom (PDL) party and the League is considered vital to the centre-right's bid to prevent the centre-left Democratic Party (PD), which is leading strongly in the opinion polls, from forming a stable government.
"Dear Silvio, we can't agree to it if you're in the field. The League cannot support you if you keep up your candidacy for prime minister," Roberto Maroni was quoted as saying in the daily La Repubblica newspaper before a meeting with Berlusconi late on Tuesday.
No official comments were made after the meeting but the rebuff delivers a potentially fatal blow to Berlusconi's hopes of keeping control of the Senate and increased speculation he could even change his mind again and rethink plans to run.
Under Italy's complex electoral laws, the PD is expected to win a strong majority in the Lower House but faces a more difficult battle to capture the Senate, which is elected on a local basis, with individual contests in each region.
In past elections, the left has struggled against the PDL-League alliance because of its traditional weakness in the richer and more populous northern regions including Lombardy and Veneto, where there are more Senate seats than in the less well-populated south and centre.
A deal between the PDL and the League could give the centre-right a chance of winning enough seats in the north to prevent PD leader Pier Luigi Bersani from forming a stable government.
"I suspect that Berlusconi might withdraw from the race," Roberto D'Alimonte, a professor of politics at Luiss University in Rome and Italy's leading expert on electoral systems, told Reuters.
"Without the League, Berlusconi has zero chance to convince voters he has even a slight chance of winning, and without the League, Berlusconi has zero chance of winning Lombardy."
On Tuesday, Berlusconi said he was still negotiating with the Northern League, which has been struggling to emerge from a corruption scandal which toppled its founder Umberto Bossi, a long-time ally of Berlusconi.
Berlusconi is scheduled to speak at a book presentation in Rome on Wednesday evening.
Maroni, interior minister in the Berlusconi's last government, has always been less close to the 76-year-old media magnate than Bossi and he said the position he had taken reflected strong resistance among grass-roots League voters.
He said the line "completely interprets the feelings of our members, officials and parliamentarians".