The United States government, in recent years, has been eager to embrace Mr. Blood. The story of his cable is part of the curriculum for incoming foreign service officers. Among the first acts of the current ambassador to Dhaka, Marcia S. Bernicat, was to present Bangladesh’s government with an official copy of the so-called Blood telegram, calling it a “reminder of the value in voicing dissenting views against existing power and authority structures.”

If Mr. Blood, who died in 2004, became a sort of poster child for dissent, it is partly because he proved to be correct, on both practical and moral grounds. In 1970, he had been appointed United States consul to what was then East Pakistan. But Pakistan’s control was slipping: Bengali nationalism was surging through Dhaka. Pakistan was flying in more and more troops. Its officers were on edge.

When Pakistan’s military began its assault on March 25, 1971, Mr. Blood’s staff was virtually paralyzed, but two officers managed to reach a wireless transmitter to report the carnage to the State Department. The reports infuriated Mr. Nixon and Mr. Kissinger, who were then seeking Pakistan’s assistance in opening up communications with China.

Mr. Blood’s cables became increasingly angry.

“Full horror of Pak military atrocities will come to light sooner or later,” he wrote, in a cable that was headed, “Selective Genocide.”

On April 6, frustrated by the lack of response from Washington, a young political officer wrote up a formal dissent cable, using a brand-new format that had been devised in response to internal turmoil over the Vietnam War. It was the first ever submitted to an American secretary of state.

But no one knew whether Mr. Blood would endorse it; as the ranking official in the mission, he had the most to lose. Mr. Kissinger’s fury did focus on the consul, Mr. Bass recounts. He was swiftly transferred to Washington, to a position in human resources.

The cable had no discernible effect on Washington’s policy, but it irreparably damaged Mr. Blood’s career. By the time he received another foreign posting, he had “lost career time” and never became an ambassador, said Howard B. Schaffer, one of 29 diplomats who signed the dissent cable in 1971.