At issue is the so-called Leahy amendment, a 1997 provision to a foreign aid bill named after its author, Senator Patrick J. Leahy, Democrat of Vermont, which bars the United States from providing training or equipment to foreign troops or units who commit “gross human rights violations” like rape, murder or torture.

Over the years, the United States has invoked the law to bar assistance to troops of major allies like Pakistan and Indonesia, and dozens of other nations. Human rights advocates have hailed the law as instrumental in preventing human rights violators from receiving American taxpayer-financed assistance.

“It’s a really important tool, but it’s not a panacea,” said Stephen Rickard, Washington director of the Open Society Foundations.

Admiral McRaven and other top officers say that they support the spirit of the Leahy amendment, but that changes in the law two years ago aimed at strengthening its enforcement have complicated their ability to train and equip foreign security forces, many of which are now front-line units fighting Al Qaeda and its affiliates.