WASHINGTON — A report describing how American forces looked the other way as powerful Afghans raped boys with impunity — an issue that long plagued the war effort in Afghanistan — prompted declarations of outrage in Washington on Monday, but officials said the problem was ultimately for Afghans to solve.

The Pentagon insisted that it never ordered troops to ignore any kind of rights abuse. But among American military personnel and civilians who served in Afghanistan, it was well known that many wealthy and prominent Afghans rape boys, often making them dress up as women and dance at gatherings during which they are assaulted — and that Western officials often turned a blind eye to the practice for fear of alienating allies.

With the bulk of American troops now gone from Afghanistan, the resignation among American officials over a practice that many described as “abhorrent” was evident on Monday. It seemed to reflect the fact that while the rape of boys may shock foreigners and infuriate Afghans, it is only one of the many problems in Afghanistan.

Over the 14 years since the start of the war, the criminality often tolerated inside the Afghan government and security forces, both of which were paid for and nurtured by the United States, has run the gamut from opium smuggling and corruption by Afghan officials to allegations of murder and torture by Afghan soldiers and police officers.