* Centre-left lead still wide but clearly shrinking
* Berlusconi support buoyed by strong TV showing
* Poll commissioned by Berlusconi puts him just 4.5 points behind
* Monti calls Berlusconi "Pied Piper" and "old illusionist"
By Gavin Jones
ROME, Jan 14 (Reuters) - Silvio Berlusconi's centre-right coalition is making rapid gains ahead of next month's elections, the latest polls suggest, increasing the possibility that even if the centre-left wins as expected it may not be able to form a stable Italian government.
A poll by the Emg agency for television station La7 showed centre-left's lead over the centre-right shrinking by 5.5 points from a month earlier to 9.5 points, La7 director Enrico Mentana said on Monday.
It was Emg's first poll since a spirited performance by Berlusconi on a critic's talk show on Thursday attracted a record 9 million viewers and huge media coverage in the following days.
Berlusconi's staff cited another poll, by the Euromedia agency, which put the gap between him and the centre-left bloc led by Pier Luigi Bersani at just 4.5 points.
Berlusconi commissions weekly polls from Euromedia, which he has used for several years. The group does not publish their surveys but its director Alessandra Ghisleri confirmed the latest results to Reuters.
She said the poll was conducted on Friday and Saturday and showed the 76-year-old media tycoon had received a strong boost of between 2 and 3 percentage points from his three-hour television appearance.
"There is no doubt that there is much more potential for Berlusconi to increase his support among right-leaning voters than there is for Bersani on the centre-left, whose support seems to have peaked," Ghisleri said.
The centre-left bloc still has a commanding lead according to most other surveys, and the prospect of Berlusconi completely closing the gap before the Feb. 24-25 vote remains unlikely.
Berlusconi's past legal troubles could also still return to damage his campaign. After the Emg and Euromedia polls were conducted, judges in Milan on Monday rejected the former prime-minister's request to halt his sex trial until after the election.
Monday's hearing - which also included an appearance from the nightclub dancer at the centre of the case - revived memories of the "Bunga Bunga" sex scandal that hung over Berlusconi's last months in office before he resigned in Nov. 2011. He denies charges of paying for sex with a minor.
His economic record also remains highly contentious.
As Berlusconi gained in polls outgoing Prime Minister Mario Monti made his most scathing attack yet against the media tycoon, calling him a "Pied Piper" who had already tricked Italians three times with unrealistic promises to slash taxes.
"The sacrifices Italians have made in the last year can be squandered in three or four months if an old, reinvigorated illusionist goes to power," said Monti during the recording of a talk show for state television.
But if Berlusconi does manage to shrug off the scandal and criticism and maintain current momentum in this election, he has a good chance of preventing Bersani from winning an absolute majority in the Senate without seeking a power-sharing deal with Monti's centrists.
Berlusconi has been closing electoral deals with a myriad of small regional parties which could stand him in good stead in the race for the upper house Senate.
The centre-left is expected to win control of the lower house, helped by a complicated electoral system that guarantees the biggest party a 54 percent majority of seats. But the Senate make-up is decided by separate battles in each region.
A survey on Sunday showed that thanks to its deal with the pro-devolution Northern League the centre-right leads by 3.5 points in the northern Lombardy region, home to the financial capital Milan and Italy's most populous area.
If Berlusconi takes Lombardy he would probably need control of just one more of Italy's 20 regions to prevent Bersani winning a Senate majority, pollsters say.
A deal between Bersani and Monti would probably be welcomed by investors who see the outgoing technocrat premier as an anchor of stability for Italy.
However, such a coalition may not be easy. Much of Bersani's Democrat Party (PD) want a sharp change of course from Monti's austerity path, and the PD's main coalition partner on the left, the SEL, regularly attack him. (Additional reporting by Paolo Biondi, Roberto Landucci and Steve Scherer.; Editing by Andrew Heavens)