For the Library of Congress representatives assigned to U.S. military intelligence at the end of World War II, it was the most exciting adventure of their lives, the closest they would come to actual combat. They were men with a mission: to scour occupied Germany for Nazi propaganda and fill in the gaps of the great American book collections.

After years spent cataloguing books and toiling in musty archives, the American librarians suddenly found themselves interrogating Nazi book collectors and confiscating enemy literature. Wearing military uniforms and serving as part of the occupying force, the dozen or so men of the Library of Congress Mission to Europe managed to ship nearly 1 million books back to Washington in a little over a year.

But now--more than half a century later--the U.S. Army captain who handed over confiscated Nazi materials to the mission says it is "undeniable" that some of the books that ended up in Washington were not mere Nazi propaganda. Rather, they had been looted from Jewish homes, libraries or synagogues by the Nazis. In recent weeks, investigators from the Department of Justice, a presidential commission on Holocaust-era assets and half a dozen private researchers have been grappling with the unsettling notion that these books are sitting unacknowledged on the shelves of the Library of Congress and other American libraries.

"The problem was that the Nazis screwed up all of Europe," says Seymour Pomrenze, a former U.S. government archivist who was in charge of a U.S. Army unit that tried to restore looted books to their communities after the war. "In some cases, when the books were marked, that was fine. We gave them back to the country [of origin]. But this was often not the case." He adds that it was "logistically impossible" to examine every crate shipped to Washington for evidence of Jewish loot.

The disputed books were part of the "working library" of a Nazi institute engaged in pseudo-scientific research into the "Jewish problem" that was seized by the U.S. Army and shipped to the Library of Congress in 382 crates, starting in March 1946. In addition, records show that the library received several thousand books in 1949 with the approval of Jewish refugee organizations as part of a general distribution of "non-traceable" Nazi loot.

The present search for Nazi-looted books has attracted much less public attention than a parallel hunt for gold and art treasures stolen by the Nazis from mainly Jewish collectors, which had greater financial value. Yet it goes to the heart of the Nazi program of cultural extermination.

During their early years in power, the Nazis simply destroyed Jewish and other ideologically suspect books, burning them in great bonfires while the former owners looked on, powerless to intervene. But the policy began to change in 1938 and 1939, when a top Nazi theoretician, Alfred Rosenberg, charged by Hitler with waging "ideological and spiritual war against Jews and Judaism," advocated using some of the books for "scholarly" purposes. Millions of books and manuscripts--including many priceless Torah scrolls--that would previously have been destroyed were transferred to Nazi libraries and museums.

Under Rosenberg's auspices, an Institute for the Study of the Jewish Question was established in Frankfurt in 1941, as part of the Nazi effort to accumulate information on a people that was already slated for extermination. Hundreds of thousands of books from looted Jewish libraries in cities like Berlin, Warsaw, Paris, Vilnius and Vienna were brought to Frankfurt to be incorporated into Rosenberg's institute.

After the war, these and several million other Jewish books fell into the hands of the victorious U.S. Army, along with vast mounds of captured Nazi documents and propaganda material. At first, there was little supervision of the allied recovery effort. When Sargent Child, newly appointed archives adviser to U.S. military commander Lucius Clay, arrived on the scene in September 1945, four months after V-E Day, he was struck by the phenomenon of American soldiers wandering through Germany "liberating books."

"I now have a better appreciation of the old stories about what the Yankees took from the South," Child wrote the Librarian of Congress, Luther Evans. "Their grandsons and those grandsons of the Rebs are following the old pattern."

By early 1946, however, the U.S. Army had embarked on an organized effort to repatriate some 3 million books that had been looted by the Nazis. They collected the loot in a warehouse in the town of Offenbach, just outside Frankfurt, under the control of Pomrenze. The Offenbach building had itself been confiscated from the chemicals conglomerate, I.G. Farben, that had manufactured the gas used at Auschwitz and other concentration camps.

The restitution effort coincided with a massive purchasing and collection drive by a consortium of American libraries led by the Library of Congress, which had been cut off from German materials for more than six years. Anxious to fill these gaps, the library dispatched a mission to Germany, armed with authority to requisition suspected Nazi collections.

"They were like kids in a candy store," says Astrid Eckert, a German PhD student from Berlin who has made a detailed study of the American restitution effort.

To bolster their authority, the Library of Congress representatives were given the rank and privileges of junior officers. "It is important" to wear uniforms, chief of mission Reuben Peiss cabled Washington in October 1945. "You get into all kinds of facilities with them and all kinds of trouble without them." In their communications back home, mission members adopted military jargon, describing Nazi libraries as "targets" and Germany as "the theater."

Many of the books shipped back to Washington by the Library of Congress Mission were purchased legitimately from German dealers. But others were confiscated from German libraries on the pretext--not always justified, according to Eckert and other researchers--of seizing "Nazi propaganda." Some of this confiscated material, researchers believe, was probably looted from Jewish collections.

Library of Congress records show that Pomrenze and his successors authorized the transfer of 382 crates of material, containing 77,000 items, from the Rosenberg Institute in Frankfurt to the Library of Congress between March and September 1946. Many of the 20,000 or so books in the institute's "working library" had come from "non-tainted" sources, including the Frankfurt public library. But researchers now believe that the library--like other Nazi collections--also contained looted Jewish books.

In accepting the Rosenberg material, Library of Congress representatives signed statements declaring that the shipments did not include Nazi-looted books "from countries other than Germany which would be subject to normal restitution procedures." But Pomrenze, who was in charge of the Offenbach depot at the time, says that it was impossible to completely separate the looted from the non-looted material. Many of the books bore no marks that would permit sorters to identify owners.

Library of Congress records fail to clearly identify the nature of the 1946 shipments from Offenbach, describing them as books on politics, law and "the Jewish question" in German, French and Italian, according to a document first discovered by Kenneth Alford, an amateur historian who has studied the question of Nazi loot.

How to dispose of the non-traceable Jewish books stored at Offenbach became a hot political issue, with Jewish organizations in America and Palestine staking rival claims. Some members of the Library of Congress Mission favored shipping the loot back to the United States. Librarian Evans did his best to steer clear of the controversy, instructing subordinates "not to touch" the heirless material until an amicable settlement could be reached.

Library of Congress officials understood very clearly that how they dealt with the Jewish book issue--and the related question of confiscated Nazi collections--could come back to haunt them. In March 1946, Peiss wrote to Evans to defend the "moral cleanliness" of his operation. "One day we are going to face accusations and we may find we have made unwise decisions on a few specific issues, but I think we shall continue to have a clear conscience."

In the end, a nonprofit organization called Jewish Cultural Reconstruction was given responsibility for distributing the half million books left behind after the Offenbach operation closed down in 1949. Many of the books were sent to the newly established state of Israel. According to JCR records, American institutions received a total of 158,111 books, of which 5,708 went to the Library of Congress.

Tracing what happened to the JCR books--and the ones received earlier from the Rosenberg Institute--is difficult. The Library of Congress did not keep track of the books that it received from Offenbach, although the JCR books were marked with a sticker inside the back cover. Some were processed into the library's own collections; others were distributed to sister institutions around the country.

Last fall, the Justice Department's Office of Special Investigations completed a report largely exonerating the Library of Congress, and concluding that it had made a good-faith effort to screen the shipments from Offenbach for "restitutable" books. That in turn triggered an investigation by the U.S. Presidential Commission on Holocaust Era Assets, which has yet to publish its findings.

More than half a century after the war, most of the original owners of the looted books are dead. Returning the books has become a practical impossibility, even supposing that the owners could be identified and traced. But some researchers believe the library could have done more to identify and catalogue the books.

David Moore, an acquisitions assistant at the Library of Congress who has studied the Offenbach records, says there should be a special entry in the library's electronic catalogue for books received from Offenbach. "These books belong to people who were murdered in the camps. If they are part of our collection, we should identify them."

Library officials say they are working closely with the Presidential Commission and would like to find "a meaningful way" of commemorating the victims of Nazi looting. "The record shows that we tried to do the right thing," says Michael Grunberger, head of the Hebraic Section of the Library of Congress. He describes the library as "an appropriate home" for the books, in view of the destruction of Jewish life and learning in Europe and its rebirth in the United States.

CAPTION: U.S. Army Chaplain Rabbi Samuel Binder inspects Torah scrolls stolen by the Nazis and recovered by the U.S. Army after World War II.

CAPTION: Michael Grunberger of the Library of Congress displays a book stamped with the Jewish Cultural Reconstruction seal.