Richard G. Hewlett, a federal historian who was co-author of three books on the Atomic Energy Commission in the decades covering the development of the atomic and hydrogen bombs, died Sept. 1 at a health-care center near his home in Bethesda. He was 92.

The cause was cardiac arrhythmia, said a friend and colleague, Brian W. Martin.

From 1957 to 1980, Dr. Hewlett was chief historian of the Atomic Energy Commission and its successor agencies, including the Energy Department. In retirement, he co-founded and became chairman of the Rockville-based historical research company History Associates.

He also was historiographer of the Episcopal Diocese of Washington and the organizer of the Washington National Cathedral archives. For the cathedral’s centennial observance in 2007, he wrote “The Foundation Stone: Henry Yates Satterlee and the Creation of Washington National Cathedral,” about the first Episcopal bishop of Washington.

Richard Greening Hewlett was born in Toledo, Ohio, on Feb. 12, 1923. As a teenager he was a budding historian who in 1937 recorded in letters home his observations from a side trip to Nazi Germany while attending an international Boy Scout Jamboree in the Netherlands.

Dr. Hewlett attended Dartmouth College before serving as an Army Air Forces radio operator and weather technician in western China during World War II.

After his discharge, he went directly to graduate school without receiving a bachelor’s degree. He completed a master’s degree and, in 1952, a doctorate in modern history at the University of Chicago. He came to Washington around that time as a civilian intelligence specialist with the Air Force, later transferring to the Atomic Energy Commission.

His history books included “Atoms for Peace and War” (1989), which was honored by the Organization of American Historians, and “Atomic Shield, 1947 to 1952” (1990).

His wife of 59 years, Marilyn Nesper Hewlett, died in 2005. He had no immediate survivors.

Dr. Hewlett was in western China in August 1945 when the first atomic bomb was detonated over Hiroshima, Japan. He got the news in a teletype notice posted on a mess hall bulletin board in his military unit. But details were skimpy, so with some friends he tried to see what they could learn from radio broadcasts.

“The reception wasn’t too good and the first station we picked up was Tokyo,” he wrote in a letter home. “There were a few words about a ‘new type American bomb,’ which was being used to slaughter ‘helpless women and children.’ The announcer gave a short spiel on how such ‘barbaric action’ violated the Hague convention and was opposed by the Pope.”

In a letter to his future wife two days later, Dr. Hewlett wrote, “Whether or not this bomb brings about any immediate catastrophic results for Japan, it seems quite clear that such a development will have a profound influence on the world in years to come.”