Italian prosecutors will on Wednesday request immediate trial for Prime Minister Silvio Berlusconi on charges of paying for sex with an underaged girl and improperly pressuring police to release her from custody.

Their application, which means the prosecutors believe they have enough evidence in the case to skip a preliminary hearing, will add to the pressure on the 74-year-old premier, whose centre-right government is hanging on to power by a thread.   

Milan prosecutors say Berlusconi paid for sex with a "significant number" of young women, including Moroccan nightclub dancer Karima El Mahroug when she was under 18, the minimum age at which it is legal to be a prostitute in Italy.

They also say he later exerted improper pressure on officials to have El Mahroug, known by her stage name "Ruby", released from a Milan police station after she was detained on separate theft allegations.

Prosecutors are expected to submit their request for an immediate trial at around 1000 GMT. Once it is filed, a judge will have five days to decide, although the deadline could be extended by a few days. If the judge agrees to the request, the trial could begin within a couple of months.

Berlusconi denies any wrongdoing and says he has never paid for sex. He says politically motivated leftist prosecutors are hounding him and trying to destroy his career, and he has refused to be questioned so far in the Ruby investigation.

The scandal has come at a difficult time for Berlusconi, whose grip on power was greatly weakened by a split in his People of Freedom party last year that cost him a secure majority in parliament.

The latest opinion polls show the investigation has damaged Berlusconi but has not delivered a knock-out blow.

A survey published in Corriere della Sera on Monday said only 34 percent of those interviewed thought the media tycoon should stay on as prime minister.   

Still, most polls say his centre-right coalition would still likely win an early election unless a fractured opposition, ranging from former neo-fascists to hardline leftwingers, managed to present a united front.

However it has added even more acrimony to an already toxic political climate which is likely to make much needed reforms more difficult to achieve and increase the chances of a crisis that could pitch Italy into early elections.   

"There is a feeling that the risk of a short circuit is getting closer every day," business daily Il Sole 24 Ore wrote in an editorial.

Leaked wiretaps from the investigation have been splashed over media with references to bundles of cash, talk of sex games and gifts that would-be starlets allegedly received after attending parties at Berlusconi's villa.   

Italian papers on Wednesday were again filled with details on the growing list of glamorous young women alleged to be connected with the billionaire premier, as text messages were leaked from a separate probe by Naples prosecutors.   

Berlusconi's defence team has presented evidence from dozens of guests saying the parties at his villa were "normal, convivial dinners".   

As for the abuse of power allegations, Berlusconi has acknowledged making a call to police on El Mahroug's behalf, saying he had been told she was Egyptian President Hosni Mubarak's niece.

His lawyers argue that he did nothing improper and was only trying to avoid a potentially embarrassing diplomatic crisis.   

If it is approved, the request for Berlusconi to stand trial is likely to trigger a lengthy legal battle, as his lawyers say the Milan prosecutors have no right to preside over the case.

"They are violating the constitution," Berlusconi's lawyer Niccolo Ghedini said late on Tuesday.

Berlusconi faces the resumptions of three other trials for corruption and tax fraud in the next month after Italy's top court struck down the automatic immunity from prosecution he enjoyed thanks to a law passed by his government. - Reuters