Almost every day a cable goes from the Justice Department to its counterpart in the Soviet Union seeking the whereabouts and testimony of Russian surviviors of Nazi prison camps.

The cables serve a single purpose. Thirty-five years after World War II, the Justice Department has embarked on a search to find former Nazis who managed to cover up their pasts and come to the United States in the 1950s and 1960s.

Not all of these Nazis were Germans. Many came from Slavic and Baltic countries and entered the United States with the 400,000 people who arrived here under the Displaced Persons Act of 1948.

"I can't tell you how many Nazis we expect to find living in the U.S.," said Allan A. Ryan Jr., head of the Office of Special Investigations of the Justice Department, "but I can tell you we're very serious about finding them."

Ryan admits that wasn't always true. He concedes that some Nazis hid behind a facade of anticommunism during the Cold War years. He also admits it took the Justice Department a long time to realize that Nazis were able to find refuge in the United States.

"There was no appreciation that there were literally hundreds of Nazi war criminals in this country," Ryan said in an interview. "Even Simon Wiesenthal [the famed Nazi hunter who lived in Vienna] didn't start making inquiries over here until the late sixties."

For years, the Justice Department's Immigration and Naturalization Service looked for Nazis in the United States with a tiny investigative staff and little money.

A year ago the task was handed over to the Office of Special Investigations, whose budget is $2.3 million this year and whose staff includes two translators, five historians, 10 criminal investigators and 20 attorneys.

Ryan gives credit for the change to Rep. Elizabeth Holtzman (D-N.Y.) who, as chairman of the House Judiciary subcommittee on immigration, refugees and international law, has been pressing since 1974 for stronger efforts to prosecute Nazi war criminals.

"The impetus came from the outside," Ryan conceded. "As a political matter, you would have to say Liz Holtzman and Joshua Eiberg [former Democratic congressman from Philadelphia] made the difference."

In the last nine months, the OSI has filed suit to strip six persons of their citizenship on grounds that they hid their Nazi pasts when they immigrated to the United States. In addition, the OSI has moved to denaturalize or deport 10 other alleged Nazi whose cases were languishing in appeals courts.

Trial dates have already been set for three of the 16 cases in litigation: Sept. 15 in Philadelphia for Wolodymir Osidach, a member of Hitler's Ukranian Police who is alleged to have murdered men, women, and children in Poland; Oct. 14 in Detroit for Viorel Trifa, now bishop of the Romanian Orthodox Church in the United States who was alleged to have incited a riot in Bucharest that killed 12,000 Jews; Dec. 15 in Brooklyn for Karl Linnas, who Justice said was commandant of a Nazi concentration camp in Tartu, Estonia.

In June, Justice Department attorneys went to Estonia and the Ukraine to take videotaped depositions of witnesses; they are to go to Israel later this month for more depositions in the Osidach case. Lawyers are now in Romania taking depositions in the Trifa case.

Apparently, nobody in the Justice Department had ever thought before this year of seeking the cooperation of the Soviets and other eastern European countries in the search for ex-Nazis. Now, the Justice Department's main source of information in its Nazi hunt are the governments of the Soviet Union, Hungary, Poland, Romania and Czechoslovokia.

"A lot of prison camp survivors live in the Ukraine, Lithuania, Latvia and Estonia," Ryan said. "Until this year, nobody had ever asked for authority to go to the Soviet Union and take the survivors' depositions."

The Justice Department also had never asked West Germany for its full cooperation in the Nazi investigation until this year. The first result of that request was spectacular. Two months ago, the Germans turned over a list of 50,000 names of men and women who served as guards in Nazi prison camps during the war.

"If any of these names turn out to be alive and living in this country," Ryan said, "I think I can make a pretty good case against him." Why wasn't the list available 10 years ago? "Nobody asked for it 10 years ago," Ryan said. "It's that simple."

Another fresh source of information has been the national archives, not only of the United States and the Soviet Union, but of the eastern European countries and Israel. Justice investigators and historians are poring through everything they get their hands on. German pay rolls, Polish enlistment papers, Romanian newspapers and even Yiddish diaries and letters have been examined, copied and translated.

Ryan refuses to say whether the lists of camp guards or any of the other documents turned over to the Justice Department by other countries have turned up any Nazis living in the United States. Says Ryan: "It's all part of our investigation."

Besides the 16 cases in litigation, the Justice Department has 266 cases under investigation. It has closed out 155 of 350 cases it inherited from the immigration service and 32 of 119 new cases it opened this year. Ryan expects to open more new cases and to close more of the cases it now considers active.

"Sometimes we find that a person we're investigating wasn't born until 1945 or came here in 1935 and never left the country," Ryan said. "Don't forget too that these people are beginning to die off."

One of Ryan's fears is that many defendants charged with Nazi pasts will die before being brought to justice. Almost all of the 16 cases in litigation are being challenged in appeals courts. One is to be heard by the Supreme Court this fall. All the defendants are in their 60s and 70s.

"Most of these people are American citizens, which means we have to revoke their citizenships before we can move to deport them," Ryan said. "That procedure alone can take three or four years with appeals, and then any move to deport can be appealed the same way all the way up to the Supreme Court."

Does Ryan think he will see the day when at least some of the alleged Nazis will be deported?

"It's an extremely lengthy procedure," he said with a sigh, "but I wouldn't be here if I didn't think we'd get some of these people deported."