Prosecutors allege Mr. Berlusconi paid Moroccan girl, known as Ruby and who was 17—year—old at the time, for sex at his villa, then called police to have her released from custody when she was picked up for theft out of concern that she would reveal their relationship.

The trial of Premier Silvio Berlusconi on charges he paid for sex with an underage prostitute, then tried to use his influence to cover it up was adjourned shortly after it opened in Milan on Wednesday.

Mr. Berlusconi did not attend the hearing, which lasted seven minutes and was devoted to formalities. The trial was adjourned to May 31.

The premier was holding a ministerial meeting in Rome to discuss Libya. He has denied wrongdoing.

The brief session was held under tight security, with some 100 police patrolling the courthouse in downtown Milan. TV crews and other media came from around the world for the opening session.

Unlike Mr. Berlusconi’s other trials, the one that opened on Wednesday puts the premier’s personal life under scrutiny, and a conviction could end his political career.

Prosecutors allege Mr. Berlusconi paid Moroccan girl, known as Ruby and who was 17—year—old at the time, for sex at his villa, then called police to have her released from custody when she was picked up for theft out of concern that she would reveal their relationship.

Both the 74—year—old premier and Ruby, who has turned 18 in the meantime, have denied having sex.

The underage prostitution charge carries a possible prison term of six months to three years. The abuse of office charge is even more dangerous- it carries a sentence of four to 12 years, and if Mr. Berlusconi is sentenced to more than five years, he would be barred from ever again holding public office.

George Clooney, Italian Cabinet ministers and aspiring starlets have been called to make appearances at the trial, though the court must decide which witnesses to admit.

Mr. Berlusconi's supporters have pledged to maintain a vigil on a traffic island opposite the courthouse where dozens have gathered for recent hearings in three other pending Berlusconi cases, all involving corruption and fraud allegations. The left—leaning opposition, meanwhile, had also planned its own anti—Berlusconi demonstration nearby for the trial’s opening.

Berlusconi sex trial could end his career

Aspiring Italian starlets and Oscar—winning actor George Clooney are being called to make appearances in Mr. Berlusconi’s trial on charges he paid for sex with an underage prostitute, then tried to use his influence to cover it up, earlier reports said.

Unlike Mr. Berlusconi’s other trials, Wednesday’s court appearance puts the premier’s personal life under scrutiny, and a conviction could end his political career. TV crews from around the world will be on hand for the opening session, even though Mr. Berlusconi himself is not attending.

“This time it is not about offshore, secret accounts and tax havens but about sex, money and power,” the Turin—daily La Stampa wrote this week.

Mr. Berlusconi is skipping Wednesday’s session, reserved mainly for formalities like setting future trial dates, calling a ministerial meeting in Rome to discuss Libya.

Even without his presence, media interest is feverish, and the Milan court overseeing the trial is holding the opening session in an auditorium usually used for ceremonial occasions in order to accommodate media.

Outside, Mr. Berlusconi’s supporters have pledged to maintain a vigil on a traffic island opposite the courthouse where dozens have gathered for recent hearings in three other pending Berlusconi cases, all involving corruption and fraud allegations.

The left—leaning opposition, meanwhile, is planning its own anti—Berlusconi demonstration nearby for the trial’s opening.

Legal experts and odds-makers alike agree that the case will be hard to prove.

Bologna political science professor Carlo Guarnieri says that convictions will require stronger evidence than what he has seen so far reported in newspapers, consisting mostly of wiretaps that allegedly place Ruby at Berlusconi’s villa outside of Milan, as well as testimony from a bevy of would—be starlets who participated in the raucous parties.

In the abuse of power case, prosecutors must prove that there was an implication of a threat of retaliation, he said.

“This is a case which is difficult to sustain in court. It is very likely that all these people involved will tell very different versions,” Prof. Guarnieri said.

Ironclad evidence would be something like a videotape, Prof. Guarnieri said. So far, no such reports have surfaced.

Prosecutors allege that Mr. Berlusconi paid for sex 13 times with Ruby, who has since turned 18, during parties that started with dinner, then generated into semi-nude dancing after which Mr. Berlusconi would choose a sex partner.

A new poll out on Tuesday, shows Mr. Berlusconi’s popularity in steady decline. The premier enjoys just 33 percent approval, compared with 50 percent last May and down from nearly 36 percent in January and 41 percent in September, after the scandal broke.

The poll by the ISPO agency for Corriere della Sera of 1,868 Italians from March 30—31 has a margin of error of 3.5 percentage points. Pollster Renato Mannheimer wrote that the erosion of public opinion can’t be pinned on any one event, but on various factors.

Mr. Berlusconi’s leadership is under challenge from his unruly coalition partners, the Northern League. Italy has also failed to garner concrete support from its European partners to combat the influx of migrants fleeing political instability in northern Africa.

In the face of sliding popularity, Mr. Berlusconi has said he intends to attend this and the other court cases against him in Milan. The premier showed up last week at a closed—door preliminary hearing in a tax fraud case, his first court appearance in more than eight years. The only images broadcast from the event showed a smiling premier greeting a hundred supporters who have set up camp outside of the courthouse.

Ruby herself is being called as a witness for both the defence and the prosecution.

Clooney was named on the list of defence witnesses because Ruby once said she had seen the Hollywood star at one of Mr. Berlusconi’s parties; the actor says he met with Mr. Berlusconi only once to get aid for Sudan’s Darfur region. It will be up to the panel of three judges, all women, to decide if the actor’s testimony would be pertinent.

Mr. Berlusconi’s defence and political allies are trying to get the trial moved out of the Milan tribunal, which the premier maintains is politically slanted against him. They want the case transferred to the Tribunal of Ministers, which deals with offenses committed by public officials in the execution of their duties.

On Tuesday, the lower house of parliament, which is controlled by Mr. Berlusconi’s conservative allies, approved a motion asking Italy’s Constitutional Court to rule on who should try the premier.

The question is not merely an academic one. Unlike an ordinary court, the Tribunal of Ministers needs the authorization of the lower house of parliament if it wants to try Mr. Berlusconi, who in addition to being premier is also a member of that chamber. Such authorization would likely be denied in the Berlusconi—controlled house.

Tuesday’s vote in parliament does not prevent the trial from opening as scheduled. The Constitutional Court could take weeks to rule.

The Milan court has no legal obligation to suspend the trial pending a decision, but could decide to do so to demonstrate respect for the higher court, Prof. Guarnieri said.

More In: International | News