The prosecutors will file their request in Milan on Wednesday. A judge must then decide whether to accept the prosecutors' request and indict the 74-year-old leader or dismiss it.
The prosecutors might request a single trial on both accusations or opt for separate procedures.
They allege that Berlusconi paid for sex with a Moroccan girl nicknamed Ruby, who has since turned 18, and then used his influence to get her out of police custody when she was detained for the suspected theft of ¿3,000 ($4,103), allegedly fearing her relationship to him would be revealed.
Ruby ultimately was released into the custody of a Berlusconi aide who also is under investigation.
Prosecutors have been considering a speedy trial for the charge that Berlusconi abused his influence when he called the Milan police, which would skip the preliminary hearing phase if they believe there is overwhelming supporting evidence. But it is also possible they would keep the two charges together.
Berlusconi denies wrongdoing, insisting he is being persecuted by politically motivated prosecutors intent on driving the conservative leader out of office.
Both Berlusconi and Ruby have denied having sex. Berlusconi said he did call police to get the girl out of custody but only due to the goodness of his heart.
The premier's supporters say he made the call to avoid a diplomatic incident because Berlusconi believed at the time that the girl was the niece of Egyptian President Hosni Mubarak.
His defense maintains the case should be handled not by the Milan prosecutors but by a special tribunal set up to deal with alleged offenses committed by public officials. Lawyer Nicolo Ghedini, speaking Tuesday evening after a meeting with Berlusconi in Rome, said the Milan prosecutors were "violating the constitutional norms," according to the ANSA news agency.
Berlusconi, a billionaire media tycoon, has been dogged by scandals related to his relationships with young women and parties at his villa. He has resisted calls for his resignation.