* Raises likelihood of centre-left accord with Monti
* Centre-right bloc gained 4 pct points in a week - poll
* Prospects of Berlusconi victory still look remote
By Steve Scherer
ROME, Jan 18 (Reuters) - Four-time Prime Minister Silvio Berlusconi extended his surge in Italy's opinion polls on Friday, increasing prospects that the centre-left Democratic Party now leading the race will have to seek a pact with Mario Monti's centrist bloc.
With a little over a month to go before the vote, Berlusconi narrowed the gap with Pier Luigi Bersani's centre-left coalition by 4 percentage points versus a week ago, but still trails by 6 percentage points, a poll published on Friday showed.
His gains follow a blitz on almost every television talkshow in Italy, where the 76-year-old billionaire has mixed blistering attacks on Monti's technocrat government, Germany and the left with promises to restore growth and scrap a hated property tax.
The surge has been reminiscent of 2006, when the flamboyant showman clawed back 10 percentage points and nearly robbed Romano Prodi of what looked like a certain victory just a month before the election.
But so far, despite similar results in several recent polls, there seemed to be little chance of an election shock giving Berlusconi a fifth term after the stew of scandals and the financial crisis forced him to step down in 2011.
"This time around, Berlusconi's ability to stage a comeback is limited," said Maurizio Pessato, vice chairman of SWG polling institute, which conducted Friday's poll.
"Berlusconi has lost a lot of credibility, more than he had before the 2006 vote, because of the failure of his government in 2011, and his personal scandals."
The poll showed the centre-left alliance of the Democratic Party and the leftist Left, Ecology, Freedom party at 33 percent, down from 34.9 percent a week ago, with Berlusconi's alliance on 27.2 percent and Monti's bloc 13.7 percent.
If the result is confirmed, the centre-left would have a solid lower-house majority.
But, due to electoral law peculiarities, Berlusconi could lose to the centre-left in the national vote tally but still win enough seats in the Senate, where voting is calculated region-by-region, to stop Bersani gaining an upper house majority.
That is important because legislation in Italy must be passed by both houses.
The centre-right has traditionally controlled Italy's most populous regions, like Lombardy, Veneto and Sicily, which are awarded more Senate seats.
This means that the centre-left, even if it garners a small Senate majority on its own, might seek Monti's support in the upper house to avoid a replay of Prodi's doomed second term, which ended after his wafer-thin majority collapsed.
"Under the rather perverse logic of this race, Monti has to hope Berlusconi does well to ensure that Bersani has to include him in a centre-left government," said Roberto D'Alimonte, Italy's top election expert.
A former European commissioner, Monti is credited by investors and foreign leaders with having restored Italy's credibility, and any role he has in a future government is likely to be welcomed by markets.
Monti and Bersani have avoided directly commenting on the likelihood of creating an alliance but they signalled that they may be willing to work with like-minded forces after the Feb. 24-25 vote, and Berlusconi's gains are making that more likely.
"The weaker that Bersani and Monti are, the more they need each other," said pollster Pessato.
Berlusconi's loss of credibility is not the only factor limiting his potential comeback. The anti-establishment 5-Star Movement led by Beppe Grillo is forecast to take 16.8 percent of the vote in Friday's poll.
Grillo is tapping into widespread anger with the political class and he is draining support from Berlusconi, Bersani and Monti, all of whom he calls "zombies" from a previous era.
With his dry wit, Monti has also turned out to be a tough campaign rival for Berlusconi. On Monday, Monti called Berlusconi a "Pied Piper" who had tricked Italians with unrealistic promises to cut taxes in the past. (Additional reporting by James Mackenzie.)