Lawyers in the special Justice Department unit that brings cases against suspected Nazi war criminals living in the United States have long been frustrated in seeking more than a glimpse of a treasure trove of documents collected after the war by the U.N. War Crimes Commission.

"For many years, we had been seeking complete and unfettered access to go to the archives and look at all of the files," said Neal M. Sher, head of the Justice Department's Office of Special Investigations (OSI). "We were barred from that under U.N. laws and regulations. They said, 'Give us a name and we'll give you a file,' which was a tedious process because we didn't know what names to ask for. It was a Catch-22."

That catch was unsnagged Nov. 13 when the United Nations agreed to open the files to accredited groups. This morning, four OSI historians are to begin making their way through 29 reels of microfilm -- between 40,000 and 50,000 documents, Sher estimates -- in the U.N. archives.

"We're going up there on Monday and going to stay there as long as it takes," Sher said. "We're going to be the first people to systematically go through it."

Sher said the documents could produce evidence for pending cases against alleged Nazis who entered the United States illegally, uncover potential new cases, or provide information about persons who should be denied entry into the United States, as Austrian President Kurt Waldheim, the former U.N. secretary general, was this spring.

Sher said that his staff had gotten an idea of the information it might find in the archives when they looked at files the United Nations provided on specific individuals, including Klaus Barbie, Josef Mengele and Waldheim.

"There are lists of camp guards. The Waldheim file had statements of witnesses. So it could be all of that: orders, organization charts, members of various units," Sher said. "From a historical point of view it can be very valuable. From a prosecutorial point of view it can be very helpful . . . . It means that when we are able to combine these records with the other records we have it will be a very unique and powerful archival holding."

Sher's office, with eight historians and twice that many lawyers, has succeeded in having 26 suspected Nazis stripped of citizenship. Nineteen have been deported or have agreed to leave the country. Recently, the office has been sending lists with the names of concentration camp guards and other suspected Nazis to the Immigration and Naturalization Service to match against the names of those who entered the United States after the war.

"Time is not on our side, so we've been redoubling those efforts and it's really paid off," Sher said. "This has been far and away our most active year."