(ANSA) - Rome, March 19 - Premier Silvio Berlusconi is hoping to draw at least half a million supporters to a rally in Rome on Saturday, ahead of regional elections in which he says voters must choose between his ''can-do government" and the "small-talking Left" and the judiciary out to nail him.

The March 28-29 regional elections in 13 of Italy's 20 regions are seen as a crucial test for Berlusconi amid signs that his popularity is slipping.

A poll published by the left-leaning daily La Repubblica last week showed his popularity has dropped to 44%, its lowest level since his government swept to power in the spring of 2008 and far below its peak of 62% in October 2008. But the media magnate-turned politician claims that privately commissioned polls show that his People of Freedom (PdL) party has regained momentum despite what he claims are attempts by alleged left-leaning magistrates to discredit him through politically motivated probes. "Our candidates will teach the Left a lesson. With our reasoning and our programmes we'll show that we can prevail over the evil, unfair and anti-democratic attitude of the Left".

Berlusconi has decided to hold the gathering in the historic San Giovanni square, the traditional meeting ground of the centre-left opposition which held its own pre-election rally in a smaller piazza last Saturday.

Berlusconi says that his will not be a protest rally but a positive show of the PdL's plans for the Italian regions, the majority of which are governed by the centre left.

He says he will ask PdL candidates running as regional presidents to commit themselves to a pact with voters to improve local bureaucracy, to build more houses and to plant millions of trees.

On Friday, he accused allegedly left-leaning magistrates of undermining Italian democracy, and pledged a wide-ranging overhaul of the judicial system over the next three years.

Leftist prosecutors, he claimed, have whipped up a new case for political ends in a bid to help the centre-left opposition's election campaign. At present, the judiciary "endangers our democracy," said the premier, stressing that "this is something we'll deal with over the next three years, with a major and radical reform of the judicial system".

Referring to a new probe against him by prosecutors in the southern city of Trani, he said his government "continues to work despite the fact that newspapers and TV shows are full of the issues that leftist magistrates have skilfully put in the spotlight".

The premier was placed under investigation this week for allegedly putting media watchdog Agcom under pressure to shut down a popular talk show on state broadcaster RAI hosted by left-leaning journalist Michele Santoro, whom Berlusconi had blackballed during his previous 2001-2005 centre-right government.

Berlusconi, who has called the probe "grotesque", denied placing undue pressure on the watchdog, saying he had simply asked it to apply the rules but that an Agcom member appointed by the opposition UDC party had vetoed his request.

"These watchdogs don't use common sense, they rule on the basis of party affiliation". According to the premier, RAI and the watchdog allow Santoro's Annozero show to get away with not giving equal-time opportunity to anyone it places on 'trial' in the programme.

"This is a disgrace that a civilised country can't put up with". Earlier this week, Berlusconi said judicial cases against him are whipped up "like clockwork" at election time and "blown up by obliging dailies".

On Friday he reiterated accusations that the judiciary and the Left had prevented PdL officials from registering Rome province candidates for the regional elections in Lazio and attempting to foil the registration of incumbent Lombardy region president Roberto Formigoni.

He said it was "absurd" that current election-filing procedures allow the judiciary to vet party documents, charging that left-leaning magistrates had "applied the rules to suit themselves". The head of the National Association of Magistrates (ANM), Luca Palamara, reacted swiftly to Berlusconi's accusations, saying the judiciary would "not let itself be intimidated by this recurrent litany".

"Magistrates apply the law, which is the basis of democracy everywhere". The House Whip for the opposition Italy of Values party, Massimo Donadi, said Berluscon's claims were "very serious".

"Trying to get Agcom to shut down an unfavourable television show is an act of a totalitarian regime which is unheard-of in any other European country".