"The Nuclear Express: A Political History of the Bomb and its Proliferation," by Thomas C. Reed and Danny B. Stillman, does not name the suspected spy, but says he was born in the United States, grew up in a foreign country, fell in with communist sympathizers during the Depression and worked at Los Alamos during World War II.

Afterward, he became "deeply involved" in the U.S. effort to develop the H-bomb, the book says.

The book, due out in January, says that co-author Stillman, a physicist who worked at Los Alamos from 1965 to 2000 and served for more than a decade as the lab's director of intelligence, took his suspicions to the FBI in the 1990s.

But the FBI inquiry was "botched beyond recognition" and went nowhere, the book says.

The FBI declined to comment.

The alleged spy is now dead, the book said.

"It's quite intriguing," nuclear historian Robert Norris told The New York Times.

"We've learned a lot about atomic spies," he said. "Now, we find out that a spy may be at the center of the H-bomb story too."