“I understood why there had been talk of protecting civilians,” the British ambassador at the time, Sir David Hannay, wrote in a cable. “But even a vastly increased and better equipped UNAMIR would find such a broad mandate difficult to fulfill,” he said using the acronym for the peacekeeping force, United Nations Assistance Mission for Rwanda.

In her April 12 cable, Ms. Albright said there was a “window of opportunity” to withdraw the bulk of the force because the airport in the capital, Kigali, was still under the control of Belgian and French troops. She advocated leaving behind a “skeletal staff that might be able to facilitate a cease-fire and any future political negotiations.”

On April 21, after a week in which 10,000 Rwandans were killed in Kigali alone, the Security Council voted to reduce the size of the force to 270 troops from 2,100. The remaining peacekeepers found themselves “standing knee-deep in mutilated bodies,” said Roméo Dallaire, the Canadian general who commanded the United Nations force.

Ms. Albright said she did not recall the specific cable pushing for a withdrawal, but she confirmed that the White House, and even more so Congress, were deeply leery of getting more involved in Rwanda after the United States’ disastrous experience in Somalia, where two Black Hawk helicopters were shot down, setting off a firefight that left 18 Americans dead. The bodies of several soldiers were dragged through the streets of Mogadishu.

At the National Security Council, Richard A. Clarke, a counterterrorism adviser to Mr. Clinton, was trying to scale back American involvement in United Nations peacekeeping operations, in part to fend off lawmakers who wanted to end them altogether.

One of the missing pieces in the newly declassified trove of documents, researchers said, are roughly 100 internal White House emails on Rwanda, which would shed light on the marching orders Ms. Albright was getting from the White House.

These emails are held by the Clinton presidential library, Mr. Blanton said, but the White House has not signed off on a declassification request he submitted nine months ago. “The American declassification system does not have any rationality built into it,” he said.