A federal judge has ruled that the Soviet Union violated international law by seizing and detaining Swedish diplomat Raoul Wallenberg, and termed "suspect" Soviet assertions that Wallenberg, credited with saving as many as 100,000 Hungarian Jews during World War II, died in prison in 1947.

The ruling by U.S. District Judge Barrington D. Parker came in a lawsuit brought on behalf of Wallenberg by his half-brother and his legal guardian. They asked for $39 million in damages and an order that the Soviet Union either produce Wallenberg or, if he is dead, his remains.

Wallenberg was seized by the Soviets as they occupied Budapest in 1945, and, according to Soviet authorities, died of natural causes in prison two years later. The lawsuit charged that testimony of former Soviet prisoners and other evidence "establishes that Raoul Wallenberg did not die in 1947 and may in fact be alive today."

Parker granted a default judgment to the plaintiffs after Soviet representatives refused to appear in the case, claiming immunity from suit in a non-Soviet country.

In a 40-page opinion filed Tuesday, Parker said he found "insufficient evidence . . . to support a definitive finding as to whether at this time, Wallenberg is dead or alive." But he called Soviet assertions that Wallenberg died in 1947 "inconsistent with and at odds with credible and uncontroverted evidence presented by the plaintiffs . . . . "

Soviet Embassy spokesman Boris Malakhov said he had no comment on Parker's ruling. But, he said, "I think that the case of Raoul Wallenberg was closed in 1957 when it was stated that Mr. Wallenberg died of a heart attack." As to reports that Wallenberg, who would now be 73, is still alive, Malakhov said, "There is no evidence except of rumors."

The Soviet Union denied in 1947 having any knowledge of the whereabouts of Wallenberg, whose efforts to save Hungarian Jews from extermination at the hands of the Nazis were funded by the U.S. In 1957, however, then-Deputy Foreign Minister Andrei A. Gromyko admitted that Wallenberg had been a Soviet prisoner and said he had died 10 years earlier.

Parker found that the Soviet Union had engaged in a "gross violation of the personal immunity of a diplomat, one of the oldest and most universally recognized principles of international law."

Although foreign governments generally are not subject to lawsuits in U.S. courts, Parker said, there are exceptions when there have been "clear violations of universally recognized principles of international law. The violation of the diplomatic immunity of Raoul Wallenberg is such a violation."

Morris H. Wolff, a lawyer for the plaintiffs, hailed Parker's decision.