Avvenire, newspaper of the Italian Bishops' Conference, said "the mere idea that a man who sits atop Italian institutions is implicated in stories of prostitution - worse yet, prostitution of a minor - is hurtful and upsetting."
In a front-page editorial, Avvenire said the probe by Milan prosecutors is like a "devastating tornado that is beating down not just on the Italian leader and a group of his friends and acquaintances, but on our country's international image."
Milan prosecutors are investigating Berlusconi on suspicion he has paid for sex with the Moroccan girl, a nightclub dancer who was a minor at the time of the alleged encounters, between February and May. The girl, nicknamed Ruby, turned 18 in November.
The prosecutors are also investigating if Berlusconi abused his powers to win the release of the girl in May from police custody, where she was held for theft.
Paying for sex with a prostitute below the age of 18 is a crime in Italy.
The 74-year old Berlusconi denies wrongdoing.
In a video message shown on Italian TV days ago, Berlusconi said the allegations were "completely groundless and even laughable." He maintained he is the victim of a persecution orchestrated by left-leaning prosecutors intent on ousting him.
Berlusconi's conservative coalition has sided with the Italian Catholic church on issues including right-to-life and the protection of traditional family values. But several scandals engulfing the premier over the past 18 months, amid allegations of wild parties and encounters with prostitutes, have strained relations.
Avvenire said Tuesday that public officials must have "a measure of sobriety and respect for oneself, all others and the office they held." In another sign of unease, SIR, the Italian bishops' news agency, called for "prompt answers" to the Milan prosecutors' questions.
Also under investigation are a former showgirl who is now a provincial government official from Berlusconi's party; a well-known journalist for one of Berlusconi's TV channels and longtime friend; and a talent agent for entertainment programs. The prosecutors allege the three helped procure and handle the prostitutes.