Pope Benedict has said he will apologise for a sexual abuse scandal that rocked the Catholic Church in Australia.

Speaking at a news conference on the plane taking him Down Under, the Pope said he would make comments similar to those made during a trip to the US last April.

He apologised for sexual abuse in the US catholic church, meeting victims and vowing to keep paedophiles out of the priesthood.

"It is essential for the Church to reconcile, to prevent, to help and to see guilt in this problem," he said.

"It must be clear that being a real priest is incompatible with this (sexual abuse) because priests are in the service of our Lord."

Victims of sexual abuse by Catholic priests and brothers in Australia have been calling on Benedict to apologise when he arrives in Sydney on Sunday for World Youth Day.

Victims of abuse by clergy plan to protest during the Pope's visit, while a group called "No Pope" will hand out condoms in protest at church doctrine and protest extra police powers during the papal visit that it says crush civil liberties.

Meanwhile, a 25-year-old sexual abuse case involving a Sydney priest was recently reopened after Cardinal George Pell, the head of the Catholic church in Australia, denied he tried to cover up the abuse.

Pell denied he misled Anthony Jones, who complained of abuse by a priest, when he wrote Jones a letter in 2003 rejecting his claim because there were no other complaints against the priest.

Pell wrote to another man on the same day upholding his abuse claim against the same priest. The priest was stood down and in 2005 convicted of indecently assaulting Jones in 1982.

On Friday, Pell reopened the case, referring it to an independent review panel.

Organisers of World Youth Day expect hundreds of thousands of young pilgrims for the event, with Pope Benedict conducting several religious events ending in a final open-air mass at Sydney's main horse racing track.

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