HISTORIANS expected the Soviet archives to be a treasure trove of information about Russian purges and politics. What they also found was a startling repository of information about the American Communist Party (CPUSA).
Yesterday, Yale University Press released ''The Secret World of American Communism,'' which proves the Soviet Union funded the American effort, maintained covert activities, and used the CPUSA to steal nuclear secrets. The book also details how some prominent Americans and journalists aided the Communist espionage effort.
''This is blockbusting material,'' says Theodore Draper, author of ''The Roots of American Communism.''
In recent years, revisionist historians have maintained that the CPUSA was a natural outgrowth of American democracy, that it was not funded by the Soviets, and that it did not participate in meaningful espionage activities.
Mr. Draper, who lives in Princeton, N.J., says the new documents ''show that the American Communist leadership was sending their records to Moscow all the time so the Comintern [the Communist International, which directed all Communist activities until 1943] was totally familiar with what was going on here.''
Draper, a historian, has read the galley proofs of the book -- which is one in a series on communism to be published by Yale. He says it offers accurate and new insights.
Harvard University Soviet expert Marshall Goldman, who has not seen advance copies of the book, says the new material may vindicate American conservatives. ''It turns out that some of those people to the right who were crying 'witches,' were right, there were witches,'' says Mr. Goldman, of the Russian Research Center.
In fact, Harvey Klehr, John Early Haynes, and Fridrikh Igorevich Firsov, the authors of the book, address the issue of the ''witch hunts'' of Sen. Joseph McCarthy. Although the authors disagree with McCarthy's ''guilt by association'' persecutions, they also conclude that ''many Americans collaborated with Soviet intelligence and placed loyalty to the Soviet Union ahead of loyalty to the United States....''
The new documents reveal:
* The CPUSA operated an espionage service called the ''Brother-Son'' network that worked with the Soviet intelligence officer who supervised the penetration of the Manhattan Project, the US super-secret effort to build the first atomic bomb. The book maintains this is the first direct proof that the CPUSA participated in the theft of American atomic secrets.
The heads of the CPUSA, Earl Browder and Eugene Dennis, assisted in that espionage. The Communist underground secretly copied confidential State Department and presidential communications. The underground also had secret informants inside several US government agencies in the 1930s and '40s.
One of the Soviet agents was Whittaker Chambers, who testified in 1948, that Alger Hiss, part of the Washington establishment, was a Soviet spy. Although the records do not prove that Mr. Hiss was engaged in espionage, the authors conclude the documents substantiate much of the information told by Mr. Chambers.
* Prominent Americans were actively involved in aiding the Soviets. The records show that the founder of Occidental Petroleum, Armand Hammer, secretly laundered cash subsidies to the CPUSA in the 1920s. In 1921, John Reed, a prominent American journalist and author of the book ''Ten Days That Shook The World,'' a romanticized view of the Bolshevik Revolution, received the equivalent of more than $1 million from Moscow.
* Other American journalists were also involved in the CPUSA. Among the journalists whose records indicate they were members of the party were Edmund Stevens, a Pulitzer Prize-winning correspondent of the Monitor, (see related story) Agnes Smedley, who was recently termed ''a freelance revolutionary operating on a global scale'' in a revisionist book, and journalist Janet Ross of the Daily Worker.
Some of this information has been surmised recently. In 1992, for example, United Press International, quoting Izvestia, a Russian daily newspaper, reported the news about Hammer. Izvestia, said Hammer had been a Comintern agent in 1921.
This information is not surprising to Carl Blumay, author of the book, ''The Dark Side of Armand Hammer.'' Hammer had a deluxe apartment near the Kremlin and the only private jet allowed to land in Moscow, which was never inspected by Soviet customs. ''They would not have given him all this if he was not doing something for them,'' says Mr. Blumay, Hammer's public relations manager for more than 25 years.
The research on the book was a time-consuming affair. The authors had access to the Comintern Archive, which has extremely detailed records, including the reports and interrogation of CPUSA leaders. In addition, the archives include a separate CPUSA collection of 4,300 files that span the years 1919 to 1944. Each file contains from 10 to several hundred pages of documents. For many years, it wasn't clear if the CPUSA archives had survived.
In 1993 the Russians culled especially sensitive documents from the archives and transferred those to the Archive of the President of the Russian Federation. Those documents, including the bulk of the post-1953 CPUSA material, are more restricted and not included in the book. The archives of the KGB are also closed.
Soviet expert Goldman says the archival material is credible. ''No one had any reason to send in lies,'' he says, adding, ''the Communist Party was very efficient at keeping records.''