"Cancelling the subject of religion from school curricula will have catastrophic consequence on society. Everybody should learn their own religion," Pope Shenouda III, Patriarch of the Coptic Orthodox Church, said at a forum organised by the Sporting Club in Alexandria, Egypt.
He also urged educational authorities in Arab countries to increase the number of subjects that teach children "how to be decent human beings".
Shaikh Muhammad Tantawi, head of one of the highest Muslim authorities al-Azhar University, in Cairo, backed the pope in his argument that religious authorities would have to shoulder the responsibility of religious instruction if such courses were omitted from school curricula.
The proposed cancellation and/or modification of religious teaching in the Arab world has triggered controversy and dispute among religious leaders.
Arabs who back the US reforms say religious teaching should be left to clerics, while those who oppose the project say it is an unacceptable bid to manipulate the Arab Muslim cultural system.
Al-Azhar has been criticised recently for its alleged role in confiscating literature, which failed to get the approval of the Egyptian censorship authorities.
"We are a consultative body in this regard. We are not policemen," said a spokesperson.
"Al-Azhar informs the government censorship body of its opinion, and there are executive governmental bodies that tackle the job of confiscating books from the shelves of bookshops."