U.S. immigration authorities were told in the early years of the Cold War that it was in America's interest to ignore the backgrounds of hundreds of East European Nazi collaborators being smuggled into this country.

In a 1951 letter to the Immigration and Naturalization Service, the late Frank G. Wisner, identified in a new book as the State Department official who brought in known war criminals, wrote:

"In wartime a highly nationalistic Ukrainian political group with its own security service could conceivably be a great asset. Alienating such a group could, on the other hand, have no particular advantage to the United States either now or in wartime."

The letter and the details of Wisner's role in recruiting Nazi collaborators to help in the Cold War struggle with the Soviet Union are in "The Belarus Secret," published by Alfred A. Knopf and written by John Loftus, a Boston lawyer who served for 2 1/2 years as a prosecutor in the Justice Department's Office of Special Investigation.

In his role as prosecutor, Loftus was assigned to hunt down Nazis who lied about their past in order to emigrate to the United States.

Loftus says hundreds of Nazi collaborators illegally were allowed into the United States by the INS. Officials of the INS could not be reached for comment yesterday.

The book gets its title from the Belarus Brigade of the Nazi SS that was made up of Byelorussians from the White Ruthenia region of the Soviet Union that the Nazis occupied from 1941 to 1944.

In the book, Loftus says that Wisner smuggled more than 300 members of the Belarus Brigade into America.

At the time, the SS organization was outlawed here.

Loftus also says Wisner lied about the backgrounds of the Nazi collaborators he brought in and openly defied Congress and President Truman's orders to keep Nazis out.

The letter Wisner wrote to the INS praises the Ukrainian Nazis for their anti-communism.

He points out that his secret Office of Policy Coordination in the State Department hid them from the Soviet Union, which attempted to have them extradited from Western Europe where they were hiding at the end of World War II.

"Luckily, the attempt to locate these anti-Soviet Ukrainians was sabotaged by a few farsighted Americans," Wisner's letter states, "who warned the persons concerned to go into hiding."

Wisner says in his letter that many Ukrainian Nazis were continuing to fight the Soviets after the war was over with the weapons and ammunition the defeated German armies had left behind.

"Over 35,000 members of the Russian secret police have been killed by the OUN [the Nazi-sponsored Organization of Ukrainian Nationalists] since the end of the last war," Wisner wrote. "In other words, the main activities of the OUN in the Ukraine cannot be considered detrimental to the United States."

Loftus says Wisner told the INS that the OUN had been falsely accused of being a Nazi organization. "The Germans used all means necessary to force the cooperation which the Ukrainians were unwilling to give. The OUN fought bitterly against the Germans . . . ," Wisner wrote.

"This was a complete fabrication," Loftus says. "The secret internal files of the OUN clearly show how most of its members worked for the Gestapo or SS as policemen, executioners, partisan hunters and municipal officials. The OUN contribution to the German war effort was significant, including the raising of volunteers for several SS divisions."

In his book, Loftus says Wisner "imported the leaders of nearly all the puppet regimes set up by the Third Reich from the Baltic to the Black Sea."

Loftus deals at length with two of Wisner's recruits, Radislaw Ostrowsky and Emanuel Jasiuk. They are buried in a White Ruthenian cemetery in South River, N.J., where they resided after being smuggled into the states by Wisner. Ostrowsky was the president of the Nazi puppet regime in Byelorussia and collaborated so closely with the Nazis, Loftus says, that there were "reports he would be named mayor of Moscow after its capture."

Jasiuk worked for the SS in Poland, where he submitted names of Polish Jews who were to be killed by the SS.

Loftus writes that even though Wisner was using "half of the CIA's budget" in recruiting his secret Nazi army, his organization was so effectively penetrated by Soviet spies that many of them lost their lives in the Soviet Union or were unmasked as American agents in Soviet radio broadcasts.

"Soviet intelligence had penetrated every corner of the Byelorussian network," Loftus writes. "The Byelorussians and the Ukrainian OUN were all riddled with Soviet agents."