WASHINGTON  Pakistan’s refusal to attack militants in a notorious sanctuary on its northwest border may have created a magnet there for hundreds of Islamic fighters seeking a safe haven where they can train and organize attacks against NATO forces in Afghanistan. But theirs is a congregation in the cross hairs.

A growing number of senior United States intelligence and counterinsurgency officials say that by bunching up there, insurgents are ultimately making it easier for American drone strikes to hit them from afar.

American officials are loath to talk about this silver lining to the storm cloud that they have long described building up in the tribal area of North Waziristan, where the insurgents run a virtual mini-state the size of Rhode Island. This is because they do not want to undermine the Obama administration’s urgent public pleas for Pakistan to order troops into the area, or to give Pakistan an excuse for inaction.

“We cannot succeed in Afghanistan without shutting down those safe havens,” Adm. Mike Mullen, the chairman of the Joint Chiefs of Staff, said last week, underscoring a major conclusion of the White House’s strategic review of Afghanistan policy last month.