Justice Department officials have told two House members an investigation is underway into "alleged misconduct" by the department's chief Nazi hunters, a sign that the controversy over U.S. handling of accused war criminals may continue long after all the principal suspects are dead.

Letters to Reps. William E. Dannemeyer and David Dreier, both California Republicans, said the department's Office of Professional Responsibility (OPR) has "initiated an inquiry" into the extradition of Andrija Artukovic, a former minister of the wartime Nazi puppet government of Croatia, now part of Yugoslavia. The State Department has told Rep. William S. Broomfield (R-Mich.) it also is investigating the matter.

Artukovic, a longtime California resident, was considered by the Justice Department's Office of Special Investigations (OSI) at the time of his 1986 extradition to be the most important war criminal in U.S. hands. Accused of ordering, and even supervising, the mass murder of Jews and Serbs, Artukovic was convicted by a Yugoslav court of responsibility for nearly 1,000 deaths and died in prison of natural causes in 1988, when he was 88, while appealing his conviction and death sentence.

Artukovic's son Radoslav, a stockbroker, has caught the attention of officials in Congress and at Justice with documents that suggest OSI officials might have withheld evidence of contradictory testimony by two key witnesses and misled a federal magistrate about OSI's role in organizing the extradition.

Justice Department spokesman Doug Tillett said he could not comment on the allegations or the letters signed by OPR counsel Michael E. Shaheen Jr. telling Dannemeyer and Dreier of the investigation.

OSI has been praised for reviving U.S. efforts to find Nazis who slipped into the United States and return them to Europe and Israel for trial. East European immigrant groups have at the same time accused the agency of falling for communist attempts to taint the reputations of anti-communist wartime leaders not responsible for the atrocities.

Some officials expected the issue to fade as cases were completed and the remaining suspects died of old age, but the Artukovic case raises the possibility of a second generation of investigations that could drag on for years.

The younger Artukovic's campaign to clear his father's name has been bolstered by a 1988 book by Milan Bulajic, a former legal adviser in the Yugoslav Foreign Ministry, who says the elder Artukovic "was sentenced for crimes that never took place."

Bulajic casts doubt on an affidavit by a former Croatian soldier, Bajro Avdic, who said he saw Artukovic supervise the machine-gun slaying of truckloads of Jews, the crushing of captured partisans under tank treads and other acts of mass murder. Bulajic published other Avdic affidavits dated 1952 and 1956 that diverge significantly from the affidavit used by OSI to win Artukovic's extradition in 1986. A 1952 Yugoslav government report said Avdic "could not be used" as a witness, the book disclosed.

Radoslav Artukovic said new information on Avdic indicates "it was OSI who dug him up, knew that he was not credible, coaxed the Yugoslavs to use him anyway, and then later in the U.S. successfully prevented any attacks upon his credibility or the truthfulness of his false statements." U.S. Magistrate Volney V. Brown granted the Yugoslav request for Artukovic's extradition in part because of assurances from OSI director Neal M. Sher that Yugoslavia, not OSI, initiated the extradition process.

Artukovic's son has complained of federal refusal, on privacy grounds, to release more information on Avdic, who still lives in Yugoslavia. He said he can prove that Yugoslav documents discrediting Avdic's testimony were in a file at the Archive of Croatia in Zagreb that was forwarded to OSI in 1984. He has a copy of a State Department cable saying the U.S. consulate in Zagreb "took possession of archival materials relating to Artukovic's wartime activities . . . packed in three boxes" to be sent by diplomatic pouch to OSI.

The other disputed affidavit came from Franjo Truhar, who discussed Artukovic's alleged involvement in the death of Serbian leader Jesa Vidic. Truhar was allegedly senile when authorities sought a statement from him in 1984. OSI instead used a statement he had written in 1952, with an assurance from a Yugoslav prosecutor that Truhar stood by the account.