The ruling means that Aloyzas Balsys, an 85-year-old resident alien born in Lithuania and now living in Woodhaven, N.Y., would face a contempt citation if he continues to refuse to explain his activities in Europe during World War II.

The ruling handed a victory to the Justice Department, which warned that extending the Fifth Amendment's protection to foreign prosecution would hurt U.S. law enforcement efforts to thwart terrorists, drug smugglers and other international criminals.

"It is an enormously important decision," said Eli Rosenbaum, director of the Justice Department's Office of Special Investigations. "The Supreme Court's ruling will have a profound implication not only for OSI's program, but for American law enforcement generally."

The decision resolves a problem that has plagued OSI's work for the last 15 years. Rosenbaum said it has been very common for suspected war criminals to invoke the Fifth Amendment and for OSI investigators to "get doors closed in our faces."

The ruling "allows the Office of Special Investigations to go full steam ahead in terms of tracking down the Nazi war criminals in our midst," said Elizabeth Holtzman, a former member of Congress who was the first to blow the whistle on the presence of Nazi war criminals in the United States and who helped create OSI, the Nazi-hunting arm of the Justice Department.

"Time is running out and this decision will have an important impact," added Holtzman, who wrote a friend-of-the-court brief for the World Jewish Congress and Holocaust survivors urging the action the justices took.

Balsys immigrated to the United States in 1961, telling immigration officials at the time that he served in the Lithuanian army from 1934 to 1940 and then lived in hiding in Lithuania between 1940 and 1944.

The Justice Department, however, suspects that during those years Balsys was a member of the Lithuanian secret police which persecuted Jews in collaboration with the Nazis.

The Justice Department has sought to question Balsys since 1993, but he has refused, arguing that his answers could subject him to prosecution in Lithuania, Israel and Germany.

A federal judge initially ruled that Balsys had to testify, but the 2nd U.S. Circuit Court of Appeals later ruled that he could invoke the Fifth Amendment's protection against self-incrimination.

In reversing the appeals court decision, Justice David Souter, writing for the court majority, said, "Concern with foreign prosecution is beyond the scope of the self-incrimination clause."

He said the court was "unable to dismiss the position of the United States in this case, that domestic law enforcement would suffer serious consequences" if fear of foreign prosecution were recognized as sufficient reason to invoke the privilege.

Justices Stephen Breyer and Ruth Bader Ginsburg dissented.