The message from Nazi security headquarters, as deciphered by Allied code-breakers, was blunt and chilling. Despite the reservations of some German officials in Rome, Nazi leaders were determined to push ahead with "the immediate and thorough eradication of Jews in Italy."

Released yesterday at the National Archives as part of a massive effort to declassify World War II war crimes records, the decrypted Nazi message of October 1943 shows for the first time that the Allies had extensive and almost contemporaneous intelligence on the Nazi roundup of Italian Jews, thanks to Britain's Enigma code-breaking operation. It provided new evidence in a long-running debate on what the Allies knew about the Holocaust at the time and whether anything could have been done to prevent the murders of millions of Jews.

The intercepted intelligence messages were circulated to a small group of British officials, including Prime Minister Winston Churchill, and also were swiftly relayed to the U.S. government. Although Churchill was an avid consumer of raw Enigma intelligence, it is not known whether he or anyone of authority in Washington read these particular reports.

Historians described the release of 400,000 pages of material--from the Office of Strategic Services, the wartime forerunner to the Central Intelligence Agency--as a major step for understanding the secret war between the Allies and Nazi Germany. The documents include some of the most closely guarded secrets of the war, dealing with OSS sources and methods, the so-called "crown jewels" of the American wartime intelligence operation.

While hailing the documents' release, which was made possible by the 1998 Nazi War Crimes Disclosure Act, historians and some U.S. officials expressed frustration over the protracted declassification process. "We are encountering some very disturbing truths" with the release of these documents, said Eli Rosenbaum, director of the Justice Department's Nazi-hunting office. "Too much has been kept secret for too long."

Among troubling questions raised by the documents is why Allied prosecutors failed to bring war crimes charges against SS General Karl Wolff, who played a key role in the deportation of thousands of Italian Jews. There has been speculation that the Allies permitted Wolff to go free because of his contacts with Allen Dulles, the Eisenhower-era CIA chief who then was serving as an OSS agent in Switzerland, and because of Wolff's role in arranging the Nazi surrender in Italy.

Wolff was held in an Allied internment camp until he was released in 1949. He lived outside Munich until he was arrested in 1962 in connection with the deaths of 300,000 Jews at the Treblinka death camp. He was tried in West Germany and sentenced to 15 years imprisonment.

"This raises some very difficult moral questions," said Elizabeth Holtzman, a former U.S. congresswoman and one of the authors of the war crimes declassification law. "Was this the beginning of an effort to protect Nazi war criminals after the war?"

The OSS documents are expected to shed more light on the extent to which successive U.S. governments made use of former Nazis such as Wolff in waging a new intelligence war against the Soviet Union and its communist allies. Previously declassified records have shown that the Allies recruited hundreds of high-ranking German scientists and helped some SS officials leave Europe for South America in return for their cooperation.

While historians have known that British cryptographers succeeded in breaking the SS security service code in the summer of 1943, the content of messages dealing with deportation of Italian Jews was previously classified. The messages were typically deciphered within three or four days. An OSS officer stationed at Bletchley Park, the British code-breaking headquarters, had access to the messages as soon as they were deciphered and transmitted them back to Washington.

The deciphered messages were supplemented by information from well-placed espionage agents, the most important of whom was Fritz Kolbe, a key German Foreign Ministry official, who made frequent trips to Switzerland, where he secretly met with Dulles. The newly released documents show that Kolbe provided Dulles with corroborating information about the liquidation of Italian Jews at the end of 1943.

Italian Jews had enjoyed a measure of protection from deportation during the early years of the war under the Italian Fascist leader, Benito Mussolini, who maintained a degree of independence from Nazi leader Adolf Hitler. But after Mussolini was overthrown in July 1943 and the Nazis occupied northern Italy, the Jews' position became much more precarious.

The intercepted intelligence traffic shows that German officials in Rome first received an order to seize the 8,000 Jews living in the capital on Oct. 6. The roundup began 10 days later on the personal order of Hitler, overruling the qualms of lower-level officials. On Oct. 20, according to the documents, the German security police commander in Italy reported that a transport of Jews had left Rome en route to Auschwitz. Postwar records show that only a few hundred Jews survived.

While there is evidence that the Allies had good intelligence about the Auschwitz death camp as early as 1943, scholars have differed over whether it filtered up to top wartime leaders, such as Churchill and President Franklin D. Roosevelt. In what was until recently the standard academic work on the subject, "Auschwitz and the Allies," published in 1981, British historian Martin Gilbert argued that the name Auschwitz did not make any impression on Allied officials until mid-1944.

Some historians believe the notion that Allied leaders were largely ignorant of the Holocaust will now have to be revised. Others go even further and argue that Churchill and Roosevelt had a moral obligation to issue much more explicit public denunciations of Nazi behavior based on the intelligence intercepts.

"A statement by Churchill or Roosevelt might have led the Jews of Rome to take seriously the evidence of imminent deportation," said Timothy Naftali, an intelligence expert at the University of Virginia, one of two American academics appointed by the National Archives to review the latest materials.

Naftali acknowledged, however, that the British and U.S. governments did not want to jeopardize their code-breaking operation.

Other records suggest that the question of Nazi persecution of the Jews was very much on the mind of Allied leaders. Churchill, who often read intercepted intelligence traffic, was constantly badgering his foreign minister, Anthony Eden, for statements condemning Nazi brutality. Eden generally opposed such statements on grounds that there was little the Allies could do to stop the Nazis from committing war crimes short of winning the war.