RMIT professor Des Cahill said his figures, based on analysing conviction rates of priests ordained from Melbourne's Corpus Christi College, closely matched a much larger American analysis of 105,000 priests which found that 4362 were child sex offenders.
The intercultural studies professor also told the inquiry that the Catholic Church was incapable of reforming itself because of its internal culture.
He said the Church's Melbourne Response abuse protocol had to go, and the state would have to intervene to achieve it.
- Called for married priests, as are being allowed now in the Anglican ordinariate within the Catholic Church, as a "circuit-breaker" that would reduce child sex abuse. The state should remove the Equal Opportunity Act exemption letting the church discriminate on grounds of marital status, he said.
- Described the Church as "a holy and unholy mess, except where religious sisters or laypeople are in charge, for example schools and welfare agencies".
- Called for an "eminent Catholic task force" of lay people to work with the Church on reform and transparency.
- Said other religions were not immune from child sex abuse, including credible anecdotal evidence of two incidents within Melbourne's Hindu community where the offending monks were "shipped back to the home country".
But the actual figure was much higher when under-reporting was taken into account, along with cases dealt with in secret by the Catholic Church. "One in 20 is a minimum. It might be one in 15, perhaps not as high as one in 10," he said.
He suggested that, though the Church tried to "fudge the figures" by including other church workers, Catholic priests offended at a much higher rate than other men. If the general male population now over 65 offended at the same rate, there would be 65,614 men living in Australia who had been convicted of child sex abuse — very far from the case.
Professor Cahill said the Church's "culture of caste clericalism" and its pyramid structure rendered it incapable of the systemic reform needed. The organisational culture was "verging on the pathological".
"Bishops are caught between canon law and civil law, and Rome has put a lot of pressure on bishops to make sure canon law and the rights of priests are being observed, but canon law has nothing to say about the rights of child victims," he said.
The Melbourne Response — the internal protocol used by the Melbourne archdiocese — was designed to protect the image and reputation of the church and to contain financial liability, and had to be changed.
"The church is incapable of reform, so the state will have to do it," he said.
He suggested a new structure involving the Office of the Child Safety Commissioner and a new "eminent Catholics task force", appointed by the Government, to work with Church leadership.
Possible candidates included former Supreme Court judge Frank Vincent, La Trobe professor Joseph Camilleri, former Geelong mayer Frank Costa, former deputy Prime Minister Tim Fischer, Mrs Diana Grollo, state chief health officer Rosemary Lester, retired Ballarat bishop Peter Connors, retired Melbourne priest Eric Hodgens and Australian Catholic University professor Gabrielle McMullin.
Professor Cahill said child sex abuse had existed in all ages, cultures and religions, shrouded in secrecy and poorly responded to by religious authorities. He said a church council in 309 AD was concerned about child sex abuse in monasteries.
One in 11 Victorians identified with a religion other than Christianity, up 68 per cent in 10 years, and Buddhists, Hindus, Muslims and Jews all had issues to do with sex abuse, especially in other countries.
In Sri Lanka, child sex abuse was rampant in Buddhist monasteries, and more than 100 monks had been charged in the past decade.
Child sex abuse had been called "India's time bomb", especially the plight of street children, while many Muslim communities were in denial, he said.
Melbourne Jewish groups were making their own submission to the inquiry.