BOMBSHELL: The Secret Story of Ted Hall and America’s Unknown Atomic Spy Conspiracy.<i> By Joseph Albright and Marcia Kunstel</i> .<i> Times Books: 400 pp., $25</i>

In years to come, historians will regard the final decade of the 20th century as an enormous watershed of revelations about U.S.-Soviet espionage, and only two events will ever explain why. The Soviet Union’s complete and devastating collapse in 1991 opened sealed records and shattered many apparatchiks’ reserve toward their old regime, to the amazement of Western and Russian researchers. Accompanying this abundance of new information was the National Security Agency and CIA’s decision between 1995 and 1996 to release cables sent during World War II to Moscow by Soviet agents in the United States; these cables had been intercepted during the war and later deciphered but concealed from public scrutiny. Even President Harry S Truman apparently never learned at the time about these so-called VENONA cables, as the program was code-named, and they would not have been released in the mid-1990s without persistent pressure from members of the bipartisan Commission on Protecting and Reducing Government Secrecy, including its chairman, Sen. Daniel Patrick Moynihan (D-N.Y.).

The sudden availability of these classified Soviet and American intelligence records has led to publication of new, informative works on Soviet intelligence activities in the United States, to which Joseph Albright and Marcia Kunstel’s “Bombshell” can now be added. The authors skillfully use both a number of VENONA documents and a wide range of written material, agent memoirs and interviews collected in post-Communist Russia, where both have worked as journalists.

Their focus is Theodore “Ted” Alvin Hall, who was, in 1944, a 19-year-old American physicist and Communist working at the top-secret Los Alamos complex and who became a major source of information for the Russians on work underway related to development of the atomic bomb. As one of the VENONA project’s most dramatic revelations, he was exposed publicly in the 1990s as a Soviet agent. Although cable decoding in 1949-50 had led Western agents to identify atomic spies Klaus Fuchs and Harry Gold, Hall--though questioned by the FBI at the time--was never arrested as a spy because of a lack of concrete evidence. Hall, to whom the Soviets assigned the code name “Mlad” or “Youngster,” was an unexpected volunteer spy who came in from the heat of the Los Alamos desert to deliver crucial materials on the American A-bomb project to a pair of Soviet couriers in 1944-45, thus joining fellow spies, German exile scientist Fuchs and American mechanic David Greenglass, who were among now-known Soviet agents at the facility.

Albright and Kunstel met Hall in 1995 and persuaded the scientist to sit for hours of interviews. (Hall had left Los Alamos in 1945 and a few years later abandoned atomic physics to pursue a distinguished career as a microbiologist at Cambridge University.) Their exchanges bolster the book’s richly documented account of Hall’s professional and personal development as well as his brief but damaging career as a Soviet agent.

Hall’s initial courier was Saville Sax, a close friend from Harvard student days and fellow Communist, who was soon replaced as Hall’s go-between by an even more self-assured young party activist named Lona Cohen. Lona and her husband, Morris, fulfilled a number of Soviet intelligence assignments in the United States during the 1940s and, in the following decade, in England under the aliases of Helen and Peter Kroger. Both were arrested, tried, convicted and imprisoned for espionage in England before finding refuge in the Soviet Union after the two governments made an exchange of agents.

The Cohens lived out their lives as retirees in Moscow, where I interviewed Morris at a KGB hospital in 1995 shortly before his death. At the time, I was doing research for my own book, “The Haunted Wood.” Although Lona Cohen worked as Hall’s courier for only a period of months in 1945 and Morris (contrary to the authors’ assertion) may not have met the physicist, the couple’s story is also told in “Bombshell,” a wise decision by Albright and Kunstel to broaden their book beyond the scope of Hall.

Despite their assiduous research into Hall’s life, the authors present their most interesting information about him in those early days when he was spying at Los Alamos before the war ended, and although they suggest he may have spied for the Soviets after the war, their evidence is less persuasive. But it is Lona Cohen, brave, quick-witted and vivacious, who served as Hall’s courier, among her many other covert duties, who is the most interesting figure in the book. “Bombshell’s” fluid narrative weaves the basically distinct threads of Hall’s life with the Cohens’ in an absorbing previously untold spy story.

“Bombshell” describes a more chaotic and haphazard espionage environment during the Cold War era than the one portrayed in the melodramatic memoirs of such ex-Communist agent-defectors as Whittaker Chambers. Hall and his friend Saville Sax roamed New York City in October 1944, during Hall’s leave period from Los Alamos, seeking a contact with Soviet intelligence to convey the data that the physicist had taken from his laboratory. Their information included a valuable list of American and British scientists then working on the atomic project. They managed to make contact with not one but two Soviet operatives, an undercover journalist and a Soviet scientist-consular official, in one of the book’s most improbable yet accurate chapters. Research in Soviet intelligence archives done for “The Haunted Wood” corroborates the authors’ version of events.

After these initial October 1944 encounters, Hall managed to meet Sax and then Cohen in New Mexico several times in 1945 with more information from the project, which supplemented and confirmed for Soviet scientists, data sent by Fuchs, a senior physicist who was also a resident at Los Alamos. Whether, as the authors argue, Hall contributed more between 1944 and 1945 to Moscow’s knowledge of the Anglo-American atomic project than did Fuchs, who had worked continuously with Soviet operatives since 1942, remains an open question awaiting a more complete release of information on atomic research from Soviet archives. Only then can we determine accurately what information came from Hall, Fuchs, Greenglass, Donald Maclean (then working on such matters in Washington) and other sources who remain unidentified.

One undeniable fact recognized by that incorrigible realist Joseph Stalin was that despite all the efforts of his Western agents, the Soviet atomic project still lagged far behind when, in 1945, the United States dropped the first atomic bombs. After Hiroshima and Nagasaki, Soviet intelligence files reveal urgent instructions to redouble efforts at obtaining secret atomic data, though with diminishing results amid tightened postwar security.

Albright and Kunstel do an excellent job of clarifying the complex processes involved in making the atomic bomb, pausing even to explain various false starts and unworkable procedures that often preceded the program’s periodic breakthroughs. The authors examine the problems with which Hall and his colleagues wrestled and are critical in understanding exactly what he and other agents at Los Alamos gave to Soviet intelligence.

At various points in “Bombshell,” Albright and Kunstel raise the difficult question of Hall’s motives and his justification. If their answers don’t provide a defense for Hall, then at the least they argue that assisting the Soviet atomic program helped create the nuclear stalemate with which the world has lived for the last half century. “Though Mlad admits he acted illegally, the crude calculus of history has yet to refute Mlad’s view that he helped decrease the risk of war.” Similar assertions are found elsewhere in the book, including an epilogue that quotes Hall’s own 1997 apologia for his actions. The scientist concluded that as a young man, he had “the right end of the stick. I am no longer that person; but I am by no means ashamed of him.”

Had the VENONA documents not exposed his identity, the authors recognize that Hall would never have acknowledged his involvement with the Soviets. What were his motives? “During 1944,” Hall wrote in his 1997 statement to Albright and Kunstel, “I was worried about the dangers of an American monopoly of atomic weapons if there should be a postwar depression” and “to help prevent that monopoly . . . [I] contemplated a brief encounter with a Soviet agent, just to inform them of the existence of the A-bomb project.”

Hall’s assertion, however, falls short of the full truth. Not only did he inform the Soviet agent-journalist Sergei Kurnakov at their October 1944 meeting about “the existence of the A-bomb project,” he also turned over a list of scientists working on it, explained to Kurnakov the principles of the atomic bomb and handed over a detailed written report on progress to date at Los Alamos. Also at this “brief encounter,” according to a report that Kurnakov wrote the next month and that emerged during my research in the KGB records, Hall also “proposed organizing meetings, if needed, to inform [us] about the progress of . . . practical experiments on explosion [sic] and its control, the [bomb] shell’s construction, etc. . . .”

Kurnakov was fascinated but still cautious, possibly fearing that this off-the-street agent might have been planted by the FBI, so he asked Hall: “Do you understand what you are doing? Why do you think it is necessary to disclose U.S. secrets for the sake of the Soviet Union?” Hall responded: “There is no country except for the Soviet Union which could be entrusted with such a terrible thing.”

This blind faith in the superiority of a communist society whose norms differed so greatly from his own country’s, a faith that almost 50 years later Hall recognized had been terribly misplaced, led him and others down the road to profound betrayal. In retrospect, that journey, which “Bombshell” chronicles, demands understanding, if not justification--compassion, if not respect.