WASHINGTON (REUTERS) - US Roman Catholic bishops on Thursday (Aug 16) called for a Vatican-led probe backed by lay investigators into allegations of sexual abuse by former Washington Cardinal Theodore McCarrick, who resigned last month.

The call comes two days after a Pennsylvania grand jury released the findings of the largest-ever investigation of sex abuse in the US Catholic Church, finding that 301 priests in the state had sexually abused minors over the past 70 years.

"Whatever the details may turn out to be regarding Archbishop McCarrick or the many abuses in Pennsylvania (or anywhere else), we already know that one root cause is the failure of episcopal leadership," Cardinal Daniel DiNardo, president of the United States Conference of Catholic Bishops, said in a statement.

The group said it would create a new way for victims of sexual abuse by members of the clergy to report allegations, and for those claims to be investigated without interference by the bishops who oversee priests who are accused of sex abuse.

It said that mechanism would involve more church members who were not members of the clergy but had expertise in law enforcement or psychology.

The Pennsylvania grand jury report on Tuesday was just the latest bombshell in a scandal that erupted onto the global stage in 2002, when the Boston Globe reported that for decades, priests had sexually assaulted minors while church leaders covered up their crimes.

Similar reports have since emerged in Europe, Australia and Chile, prompting lawsuits, sending dioceses into bankruptcy and undercutting the moral authority of the leadership of the Catholic Church, which has some 1.2 billion members around the world.

One prominent Catholic group, which was formed to promote parishioner's voices after the abuse scandal first emerged, expressed concern over how the new abuse reporting process would work.

"I take everything with a huge grain of salt, but this is the strongest statement that I can recall involving laity and law enforcement," said Nick Ingala, spokesman for the Voice of the Faithful group, in a phone interview.

He said it would be critical that any new review process be independent of clerical influence, but added, "I don't know how they are going to work that out."

McCarrick last month became the first cardinal in living memory to lose his red hat and title.

Other cardinals who have been disciplined in sexual abuse scandals had kept the honorific "Your Eminence."

The Vatican has not yet publicly commented on the Pennsylvania grand jury report.

Its normal practice is to leave such comment to national bishops' organisations.