Lyon (AFP) - Accused of sexually abusing dozens of boy scouts in the 1970s and 80s, a French Catholic priest confessed in court Tuesday to "caresses" he knew were forbidden, and said for 20 years "it happened every weekend".

At scout camps, "it could be four or five children a week," Bernard Preynat, 74, told a court in Lyon on the first day of his trial for preying on boys.

"For me, at the time, I was not committing sexual assault but giving caresses, hugs. I was wrong."

Sitting up straight in the dock, Preynat's voice quavered as he admitted the interactions "did bring me sexual pleasure."

But while he knew the actions were forbidden, he said he only finally understood that they were illegal thanks to "the accusations of the victims".

The accusers were aged seven to 14 when the alleged crimes were committed between 1971 and 1991, when Preynat was a scout leader in Lyon.

The allegations against him sparked the biggest crisis in the French Church in decades and last year saw a cardinal convicted of covering up the alleged crimes.

Preynat was defrocked by the Church last July.

Former scouts have claimed he touched and kissed them and forced them into reciprocal fondling while they were in his care, including at camps. He denies ever kissing the boys on the mouth.

Francois Devaux, one of Preynat's accusers and the founder of a victims' organisation, spoke of the "hell" his parents, who had alerted church authorities about his experience, had lived through, and his own "very difficult, very complicated" adolescence as a result.

He said he had tried to commit suicide.

"I think I used to be a bright child. After, I lived a very dark life... flirted with dangerous things," Devaux testified. He was ten when it happened.

"Pain, anger... Whatever the court decides, the harm and the trauma suffered in my childhood will continue. My responsibility is that this must never happen again," said Devaux.

Ten accusers and several victims' associations are civil parties to the proceedings.

Cardinal appeals

Emmanuelle Haziza, a lawyer for complainant Pierre-Emmanuel Germain Thill, said the court was "faced with the biggest sexual predator of the Lyon region," and said he has admitted to "having touched hundreds and hundreds of children."

The case first came to light in 2015 when a former boy scout went public with allegations that Preynat had abused him as a child 25 years earlier.

A trickle of initial testimony soon turned into a deluge, with more than 80 other people coming forward with allegations of abuse.

In March last year, a Lyon court found French cardinal Philippe Barbarin guilty of failing to report the claims against Preynat.

Barbarin, the city's archbishop and the most senior French cleric to get caught up in the global paedophilia scandal, was handed a six-month suspended sentence.

During the trial, the cardinal said he had confronted Preynat about the abuse "rumours" in 2010 but let the matter go after the priest insisted he had changed.

In 2014, after meeting one of the victims, Barbarin contacted the Vatican about the affair. Preynat was suspended until September 2015. 

Civilian authorities charged him with sexual abuse in 2016. He risks ten years in prison.

Pope Francis rejected Barbarin's offer to resign, saying he would await the outcome of an appeal by the cardinal, who has stepped back from Church duties.

Two other senior French religious figures have been convicted of failing to report child abuse in the past: the archbishop of Bayeux-Lisieux, Pierre Rican, in 2001, and the former bishop of Orleans, Andre Fort, last year.