A few weeks later, Ms. Rice again stepped in to protect Mr. Kagame. After delaying for weeks the publication of a United Nations report denouncing Rwanda’s support for the M23 and opposing any direct references to Rwanda in United Nations statements and resolutions on the crisis, Ms. Rice intervened to water down a Security Council resolution that strongly condemned the M23 for widespread rape, summary executions and recruitment of child soldiers. The resolution expressed “deep concern” about external actors supporting the M23. But Ms. Rice prevailed in preventing the resolution from explicitly naming Rwanda when it was passed on Nov. 20.

Mr. Knopf, the spokesman for Ms. Rice, said the view of the United States was that delicate diplomatic negotiations under way among Rwanda, Congo and Uganda could have been adversely affected if the Security Council resolution explicitly named Rwanda. “Working with our colleagues in the Security Council, the United States helped craft a strong resolution to reinforce the delicate diplomatic effort then getting under way in Kampala,” Mr. Knopf said.

The negotiations subsequently fell apart, and the M23 continued to make gains in eastern Congo. Last week, the M23 withdrew from Goma but left behind agents and remain in range of the city.

Mr. Knopf declined to confirm or deny the account offered by the United Nations diplomat about the conversation between Ms. Rice and the French ambassador. But he said that “Ambassador Rice has frequently and publicly condemned the heinous abuses perpetrated by the M23 in eastern Congo,” adding that the United States was “leading efforts to end the rebellion, including by leveling U.S. and U.N. sanctions against M23 leaders and commanders.”

Ms. Rice’s critics say that is the crux of the problem with the American response to the crisis in Congo: it ignores, for the most part, the role played by Mr. Kagame in backing the M23, and, as it happens, risks repeating the mistakes of the genocide by not erring on the side of aggressive action. “I fear that our collective regret about not stopping the Rwandan genocide, felt by all of us who worked for the Clinton administration, led to policies that overlooked more waves of atrocities in the Congo, which we should equally regret,” said Tom Malinowski, the Washington director of Human Rights Watch, who has worked closely with Ms. Rice both in the Clinton administration and after.

“For almost 20 years now, the premise of U.S. policy has been that quiet persuasion is the best way to restrain Rwanda from supporting war criminals in the Congo,” Mr. Malinowski said. “It might have made sense once, but after years of Rwanda doing what the U.S. has urged it not to do, contributing to massive civilian deaths, and ripping up U.N. resolutions that the U.S. sponsored, the time to speak plainly and impose penalties has come.”