The Catholic Church on Thursday is expected to release its new rules to try to prevent clergy from abusing children, a source close to the Vatican told CNN.

The rules will be aimed more at firming up existing practices, said the source, who asked not to be named because the source was talking about the regulations before they are made public.

The Vatican will add the possession of child pornography to the list of most serious crimes, declare the abuse of any mentally retarded person to be as bad as the abuse of children, and double the statute of limitations on the Vatican's prosecution of suspected abuse.

The Vatican also plans to make it a major crime against the church to ordain a woman as a priest, the source said.

Some critics of the Catholic Church have said that having women in the hierarchy could have helped prevent clerical child abuse. It is not clear if the hardening of the Vatican's longstanding line against women priests is related to the accusation.

The new rules on child abuse are a response to accusations against priests across Europe and the United States in the past several years, and come not long, in Vatican terms, after the last set of such rules was issued in 2001.

Pope Benedict XVI was a key in drafting the 2001 rules, when he was Cardinal Joseph Ratzinger.

The source said the new rules were designed primarily to set down in canon law what the church already practices.

They deal only with how the church handles allegations of misbehavior by clergy, the source said, explaining that it did not change existing Vatican policy of also reporting suspected child abuse to civil authorities.

Abuse victims are already saying the changes don't go far enough.

"There needs to be massive overhaul, not mere tweaking,of how the church

deals with abuse and cover-up," said Barbara Dorris, of the Survivors Network

of those Abused by Priests.

"As long as bishops can ignore and conceal child sex crimes without punishment, they'll keep ignoring and concealing child sex crimes," she said last week, responding to media reports about what the new guidelines would say.

"The focus needs to be on catching predators more quickly, involving secular law enforcement, and preventing recklessness and deceit by bishops, who can and should take many steps to protect the vulnerable long before the defrocking process begins," she said.

Thousands of people have come forward in the United States, Ireland, the Netherlands, Austria and the pope's native Germany to say they were abused as children by Catholic clergy.

The crisis has particularly shocked deeply Catholic Ireland, where three government-backed investigations have uncovered physical and sexual abuse stretching back decades.

Police in Belgium recenty raided the headquarters of the Catholic Church there, and later spent 10 hours questioning the cardinal who used to head the Belgian Catholic Church.

The pope has repeatedly said the Vatican will seek justice for victims.

Last month he said the church must promise "to do everything possible" to ensure that the sexual abuse of children by Catholic priests "will never occur again."

Benedict said the church must "insistently beg forgiveness from God" and from victims for the sexual abuse committed by Catholic priests. He also said priests must be more thoroughly vetted before joining the ministry.

CNN's Hada Messia, Richard Allen Greene and the CNN Wire Staff contributed to this report.