THE HAGUE, Netherlands – Up to 20,000 children endured sexual abuse at Dutch Catholic institutions over the past 65 years, and church officials failed to adequately address it or help the victims, according to a long-awaited investigative report released Friday.

The findings detailed some of the most widespread abuse yet linked to the Roman Catholic Church, which has been under fire for years over abuse allegations in Europe, the United States and elsewhere.

Based on a survey of 34,000 people, the report estimated that 1 in 10 Dutch children suffered some form of sexual abuse — a figure that rose to 1 in 5 among children who spent part of their youth in an institution such as a boarding school or children’s home, whether Catholic or not.

“Sexual abuse of minors,” it said bluntly, “occurs widely in Dutch society.”

The findings prompted the archbishop of Utrecht, Wim Eijk, to apologize to victims on behalf of the Dutch church, saying the report “fills us with shame and sorrow.”

The abuse ranged from “unwanted sexual advances” to rape, and abusers numbered in the hundreds and included priests, brothers and lay people who worked in religious orders and congregations. The number of victims who suffered abuse in church institutions likely lies somewhere between 10,000 and 20,000, according to the probe, which went back as far as 1945.

The commission behind the investigation was set up last year by the Catholic Church under the leadership of a former government minister, Wim Deetman, who said there could be no doubt church leaders knew of the problem. “The idea that people did not know there was a risk … is untenable,” he told a news conference.

Deetman, a Protestant, said abuse continued in part because bishops and religious orders sometimes worked autonomously to deal with the abuse and “did not hang out their dirty laundry.” However, he said the commission concluded that “it is wrong to talk of a culture of silence” by the church as a whole.

Colm O’Gorman, executive director of Amnesty International in Ireland and a victim of clergy abuse, criticized the Dutch inquiry because it was established by the church itself.

“It is the Dutch government that should be putting in place a meaningful investigation,” O’Gorman said.