But despite the setback, most polls show the center-left coalition led by the Democratic Party (PD) still well ahead of Silvio Berlusconi's center-right.

Monte dei Paschi revealed last week that it had suffered nearly $1 billion of losses in complex derivatives deals entered to massage its accounts because of severe financing problems.

The scandal has generated an explosive political controversy ahead of the Feb 24-25 election, with rival politicians trying to exploit the issue to undermine the center-left.

An Emg poll conducted on Jan 24-25 and released on the La7 television channel on Monday showed support for the PD had fallen to 30.7 percent, 1.1 percent down on a week earlier.

But support for the center-left coalition overall slipped only 0.3 percentage points to 36.8 percent, with other left wing parties such as Nichi Vendola's Left, Ecology, and Freedom (SEL) group gaining ground.

Berlusconi's People of Freedom (PDL) party rose 1 percentage point to 20 percent, but support for the center-right coalition overall remained stable at 28 percent, still 8.8 points behind the center left led by Pier Luigi Bersani.

A sustained drop in support for Bersani's coalition would make it more likely for him to have to seek a power-sharing deal with outgoing Prime Minister Mario Monti's centrist grouping to form a stable government after the election.

Monti's coalition slipped 0.5 percent compared to a week earlier to 9.6 percent, the Emg poll showed.

Other polls released this week showed similar trends. A survey carried out by the Tecne research institute for SkyTG24 showed the difference between the center left and center right had narrowed to 6.2 percentage points.

(Reporting By Catherine Hornby; editing by Barry Moody)