VATICAN CITY -- Pope Benedict XVI was to have said he was the "voice of moral reason" in a speech he decided not to give at Rome's secular La Sapienza university, according to a text released Wednesday by the Vatican.

The text was released the day after the head of the Roman Catholic Church cancelled an appearance at the prestigious university in the face of protests by physicists and students who claimed his presence was inappropriate in a secular setting.

The protesters were especially opposed to a papal appearance on the day -- Thursday -- that the huge university was to launch a new academic year amid traditional pomp and ceremony.

"The pope, as pastor of his community, has become more and more a voice of humanity's moral reason," Benedict said, adding: "The wisdom of great religious traditions ... cannot be thrown into the dustbin of the history of ideas with impunity."

The death penalty, the topic on which the pope had planned to speak, was not mentioned in the dense five-page text released by the Vatican.

In it, Benedict rejected the idea that "theology, whose message is addressed to reason, be confined to a private sphere, whether big or small."

La Sapienza "used to be the university of the pope, but today it is a secular university," Benedict wrote, adding that it was "independent of political and eccesiastical authorities."

Founded in 1303 by Pope Boniface VIII, La Sapienza became a secular institution in 1870. Its student body now numbers some 138,000.

The 80-year-old pope also warned that people in the West had so much knowledge and power that they "capitulate before the question of truth" and place far too much emphasis on "usefulness."

At La Sapienza, the pope would "not seek to impose faith in an authoritarian way (but) to keep awakened (people's) sensitivity to the truth and to invite reason to go in search of the true, of the good, of God."

Many scientists criticize the intellectual, conservative pope, a respected theologian, for a series of positions he has taken that they say subordinate science and reason to faith.

The protest against the visit was spearheaded by physicist Marcello Cini, a professor emeritus of La Sapienza, who wrote to rector Renato Guarini complaining of an "incredible violation" of the university's autonomy.

Sixty-seven professors and researchers of the university's physics department, as well as radical students, joined in the call for the pope to stay away.

The Catholic diocese of Rome on Wednesday called on the city's faithful to rally in support of the pope in St Peter's Square on Sunday when he is to give his weekly Angelus blessing.

Also Wednesday, the Vatican made public extracts of a letter from Italian President Giorgio Napolitano to the pope in which he expressed "sincere, deep regret" over the cancellation and the "unacceptable displays of intolerance" by La Sapienza's protesting professors and students.

Prime Minister Romano Prodi had led unanimous denunciations of the protest by Italy's political class, echoed widely Wednesday by the country's main dailies.