Boston ? It is likely that more than 1,000 people were molested by priests and workers in the Boston Archdiocese over six decades, a figure the Massachusetts attorney general termed “staggering” as he issued a report Wednesday blaming Roman Catholic leaders for the crisis.

“The mistreatment of children was so massive and so prolonged that it borders on the unbelievable,” Atty. Gen. Tom Reilly said.

The report ends a 16-month investigation by Reilly’s office and a grand jury session that was convened last summer to consider charging church leaders.

The extent of abuse the report outlines dwarfs what’s been found in other dioceses. Still, while the document provides a comprehensive look at what Catholic officials knew, when they knew it and how they covered it up, Reilly said he was hamstrung by state laws that were too weak to allow criminal charges to be filed against the hierarchy.

Cardinal Bernard Law, who resigned last December, “bears the ultimate responsibility for the tragic treatment of children that occurred during his tenure,” Reilly said in the 76-page report.

The cardinal, he said, was aware of the abuse even before he arrived in Boston as archbishop in 1984 — and he and his inner circle were actively informed about complaints against numerous priests. With only rare exceptions, did any of Law’s senior assistants advise him to take steps that would put a halt to what became the systematic abuse of children, Reilly said.

“The choice was very clear, between protecting children and protecting the church. They made the wrong choice,” he said. “In effect, they sacrificed children for many, many years.”

Reilly also warned that the archdiocese’s new abuse policy, announced in May, is insufficient to guarantee the safety of children. Among other problems, the attorney general said the archbishop retained too much control over investigations, discipline and members of a lay review board.

The Rev. Christopher Coyne, a spokesman for the archdiocese, said the church had already taken “substantial steps” to prevent child abuse.

Law’s successor, archbishop-elect Sean Patrick O’Malley, is to be installed next week and has pledged to heal the fractured archdiocese.

“The Archdiocese of Boston reiterates its commitment that the archdiocese will treat sexual abuse of a child as a criminal matter, that it will end any culture of secrecy in the handling of such matters … and that the archdiocese is committed to work at every level to ensure the safety of children,” Coyne said.

The archdiocese itself documented 789 allegations of sexual abuse made against 237 priests and 13 other church workers from 1940 to 2000.

When evidence from other sources was included, the number of victims rose to at least 1,000, Reilly said.