ALTOONA, Blair County — Two Roman Catholic bishops who led a central Pennsylvania diocese helped cover up the sexual abuse of hundreds of children by more than 50 priests or religious leaders during a 40-year period, according to a grand jury report issued Tuesday.

The 147-page report on sexual abuse in the Altoona-Johnstown Diocese was based partly on evidence from a secret diocesan archive uncovered through a search warrant executed in August, said Pennsylvania Attorney General Kathleen Kane, who announced the findings.

“These predators desecrated a sacred trust and preyed upon their victims in the very places where they should have felt most safe,” Kane said in a statement. “Just as troubling is the cover-up perpetrated by clergy leaders that allowed this abuse to continue for decades.”

No criminal charges are being filed in the case because some abusers have died, the statute of limitations has expired and, in some cases, victims are too traumatized to testify, she said.

The report is especially critical of Bishops James Hogan and Joseph Adamec. Hogan, who headed the diocese from 1966 to 1986, died in 2005. Adamec, who succeeded him, retired in 2011.

Adamec cited possible self-incrimination in refusing to testify before the grand jury in November. But in a court filing, his attorney said the accusations against the retired 80-year-old bishop are unfounded.

Adamec required 14 priests accused under his watch to undergo psychiatric evaluation, the filing said. Nine of them were suspended or removed from ministry, and the five who were reinstated never reoffended, his attorney wrote.

The Altoona-Johnstown report said Hogan covered up abuse allegations by transferring offending priests, including by sending one accused clergyman to a school for boys.