By Iris Chang

Basic Books. 329 pp. $27.50

IN JUNE, 1950, the FBI accused a brilliant Chinese scientist in California who had helped pioneer the American space age of being a Communist Party member. Despite a lack of evidence against him, Tsien Hsue-shen was held under virtual house arrest for five years and then deported to China, a victim of the McCarthy era. The United States lost a scientific genius; China gained one.

Tsien, who had once sought U.S. citizenship, quickly became one of the most powerful scientists in China, guiding the development of China's nuclear missile, satellite and space programs. In the 1960s, it was Tsien Hsue-shen (whose name is also written as Qian Xuesen), who proposed construction of the infamous Haiying missile -- commonly known as the Silkworm -- that eventually menaced American ships during the Gulf War.

Iris Chang writes compellingly of Tsien's fascinating life in Thread of the Silkworm, and grapples with many of the contradictions that beset this disciplined yet impulsive, sensitive yet arrogant man. She begins with his birth into a wealthy Chinese silk merchant's family early in this century and ends with his ascendancy as a kind of Chinese Wernher von Braun. Along the way, she provides a history of China's nuclear missile program as well as a description of the political climate in the 1950s and '60s that shaped the thinking of some of today's top Chinese scientists and military leaders.

During his first year back in China, Tsien worked under incredibly primitive conditions as director of a fledgling institute devoted to aerodynamics for defense purposes. According to Chang, "there was only one telephone in the entire building, which rang incessantly for Tsien. His office was on the fourth floor and the phone was on the ground floor and he had to run up and down those stairs to answer the phone. There was also little usable equipment. The institute purchased some desk calculators that had to be wound up by hand . . ."

Although Chang has dispelled many of the mysteries surrounding Tsien Hsue-shen, he emerges from this book as an enigmatic figure. Apparently betraying his own principles once he returned to China, he bought into the communist system with a vengeance.

"How stark the contrast between the young Tsien and the old," Chang writes. "The young Tsien dreamed of a world of peace and equality. The older Tsien lived in a world governed by regimented hierarchy and helped manufacture the weapons of world destruction. The young Tsien was both Chinese and American, at heart a citizen of two countries. The older Tsien felt alienated by both."

Chang finds evidence that Tsien denounced a former friend and colleague in order to protect himself during one of Mao Zedong's periodic crackdowns on intellectuals, made statements through the years to suit the prevailing Maoist political dogma, and then gradually became the kind of unquestioning bureaucrat that he once so despised in the United States during the McCarthy era.

After the Chinese army attack on protesters at Tiananmen Square in 1989, Tsien denounced the demonstrators as "evil elements" and, in line with prevailing orthodoxy, branded the dissident astrophysicist Fang Lizhi "the scum of the nation."

Tsien's personal life remains a mystery, according to Chang. Only a handful of friends see him in the privacy of his home in Beijing and then only rarely. Since his return to China, Tsien has declined to give interviews to foreign reporters or scholars and has thwarted attempts by Chinese biographers to tell his story. Tsien has instead given permission to his secretary to work on a biography of him after his death.

Chang's sleuthing has its limits. She does not claim to know the full extent of Tsien's contribution to the Chinese missile program or the definitive story of his dealings with the U.S. government during the McCarthy period. Many of her Freedom of Information Act requests are still pending at the FBI.

Not surprisingly, Chang was unable to interview Tsien. But she did succeed in reaching relatives, friends, colleagues, students and employees of the scientist who were eager to talk about him. Even a few Chinese rocket scientists were willing to talk as long as they remained anonymous. She also found a wealth of documents in U.S. government and university archives, a large U.S. Army file and portions of his FBI file tucked away in a U.S. Customs Service file.

Perhaps it was inevitable, Chang concludes, that missile technology would proliferate worldwide with or without Tsien's help. But "who knows," she asks, "how many potential Tsiens there are in universities in the United States today, trying to decide between staying in the country to continue their research, or returning to their home nations to contribute to their defense effort, their fates determined by the whim of an immigration officer or a budget cut."

She also concludes that we will never know Tsien's true feelings toward the United States: "Publicly, Tsien has denounced the country that deported him for its capitalist system, but privately, quietly, unknown to most people in China, Tsien has permitted both his children . . . to return to the United States for further education -- a sign that he may be far less hostile toward the United States than he makes out to be."

But Tsien's son, Yucon, an American citizen by birth, told Chang that only one thing could possibly bring his father to revisit the United States: an apology from the U.S. government to atone for treating Tsien like a criminal.

When she began her research on Tsien Hsue-shen several years ago, Chang could not have foreseen the current tensions in China's relations with the United States or the growing concern among some experts in this country over China's military strength. Her book reminds us that while we now know a great deal about China's military hardware, we still need to know much more about the thinking of its military leaders and defense industry scientists. Like Tsien, some of those scientists and military men are extremely nationalistic and, according to some accounts, convinced that the United States has once again become China's leading adversary.

Daniel R. Southerland was Beijing bureau chief of The Washington Post from 1985-1990; he is currently a reporter for the business section. CAPTION: Tsien Hsue-shen, ca. 1949