The Justice Department said yesterday that it has been investigating "for some time" whether Soviets who collaborated with the Nazis were brought into the United States after World War II by U.S. intelligence agencies and whether those agencies lied to Congress about their involvement in such Soviet emigration.

"Widespread publicity has been given to allegations that a number of Byelorussians . . . who took part in Nazi persecution of minority groups were subsequently assisted by U.S. intelligence agencies to enter the U.S.," the department said in a prepared statement.

"It has also been alleged that in recent years attempts by Congress, through the General Accounting Office, to obtain information about these persons have been deliberately thwarted by executive branch agencies.

"Both matters have been under investigation for some time by the Department of Justice's Criminal Division," the statement said.

The statement was the department's first formal response to charges aired Sunday on CBS television's "60 Minutes" by former Justice Department prosecutor John J. Loftus. He said that as many as 300 White Russian Nazi collaborators were brought to the United States after the war by the State Department and U.S. Army intelligence services to be used as spies, informants and propagandists against the Soviet Union during the Cold War.

Loftus also charged that the same intelligence agencies covered up the smuggling operation and lied to Congress when asked the whereabouts of the Byelorussians who had been Nazi collaborators before emigrating here.

Now a Boston attorney in private practice, Loftus had worked for the department's Office of Special Investigations until November, 1980. He has written a book about the smuggling operation called "The Belaris Secret." Belaris was the name of a Byelorussian division that fought for the German SS in World War II.

In its statement, the Justice Department said it has been investigating for almost a year the charge that U.S. intelligence agencies may have covered up the smuggling operation and for about 2 1/2 years the charge that the Byelorussians had entered this country illegally.

"As to the allegations that executive branch agencies engaged in a cover-up to prevent Congress from obtaining accurate information about the emigres, the department's Office of Public Integrity began inquiries last year and those efforts are continuing," the statement said. "No more can be said about that matter at this time."

Justice also said it has been actively investigating whether Byelorussians entered this country illegally, with or without the help of U.S. intelligence agencies.

" . . . This [investigation] necessitates the painstaking process of assembling a case [against these persons] that will prevail in federal court. If and when evidence of that strength is assembled in the investigations of Byelorussian emigres, charges will be filed against them, just as they have been in more than two dozen other cases in the last three years," the department said.

On "60 Minutes," Loftus charged that the Office of Policy Review, formerly a covert intelligence unit in the State Department, had smuggled in about 300 Nazi collaborators, many of whom had been Nazi-appointed officials in the Soviet Republic of Byelorussia, occupied by Germany in World War II.

Loftus also said federal agencies including the FBI, the Army and the State Department had helped the Byelorussians become naturalized citizens.

In March, 1977, then-Rep. Joshua Eilberg (D-Pa.) asked the Pentagon for information about 48 suspected Nazi war criminals, including a Byelorussian he called Emmanuel Jastuk, in reality Emmanuel Jasiuk, mayor of the Byelorussian district of Stulpche.

The Army told Eilberg it could find no record of an Emmanuel "Jastuk" nor any of anyone with eight other variations of the last name. "We conducted the search in good faith, based on the information requested. We did not lie," an Army spokesman said.

In a telephone interview, Loftus said Jasiuk had long been on the computerized index of the Defense Investigative Service and that the name could have been turned up "with a simple phone call."

Loftus said Jasiuk was also listed in an Army file with the Immigration and Naturalization Service that bore a note saying the file contained defense information and could not be turned over to Congress.

Rep. Barney Frank (D-Mass.) charged on "60 Minutes" that Jasiuk "helped murder innocent Jewish people" as mayor of Stulpche.