Yugoslavia's communist government updated evidence about Kurt Waldheim's record as a World War II German Army officer after his rise to prominence as an Austrian diplomat but consistently avoided pressing or publicizing its war crimes charges against him, according to historians, diplomats and Yugoslav officials here.

Twenty years after filing a war crimes case against Waldheim with a United Nations commission, state prosecutors reviewed and supplemented their evidence and privately forwarded new material to the United Nations in 1967, the year before Waldheim became Austria's foreign minister, knowledgeable sources here said.

When charges against the former U.N. secretary general were publicized last month, the prosecutors undertook a new review of the case, allowed the public release of several documents and forwarded files to the Austrian government, the sources said.

Yugoslavia neither pressed its case against Waldheim in 1967, however, nor spoke out publicly about the charges when he was elected as U.N. leader four years later. Despite pressure from investigators both at home and abroad, authorities here have recently refused to explain their evidence against Waldheim or reveal whether the late president Tito, who dealt extensively with Waldheim, was aware of the long-pending case.

Yugoslav media, which published several documents obtained with official assistance from state archives last month, have since been told by authorities to tone down their coverage, editors here said.

Government officials insist they have nothing to hide about their actions. Instead, they say, their low-profile approach has been dictated by the inconclusive record of Waldheim's actions on Yugoslav territory. Belgrade, they add, has an overriding priority of maintaining good relations with Austria, a major trading partner and neutral buffer amid nonaligned Yugoslavia's three Soviet Bloc and two NATO neighbors.

"Everyone is expecting that Yugoslavia should say something on the eve of an election in Austria, our neighbor. But why should we?" asked Mladen Gavrilovic, the diplomatic editor of the government news agency Tanjug. Waldheim is a candidate in Austria's election for president this week.

"What's important for us is to maintain relations with a neighboring country," said Gavrilovic, who is the nominal author of the only government-authorized account of Yugoslavia's action in the Waldheim case.

Gavrilovic and other officials said that evidence that Waldheim was involved in the murder of civilians and burning of villages in southern Yugoslavia during 1942 and 1944 was too weak to merit either prosecution or a public attack on the Austrian.

They added that the Soviet Union and western countries, including the United States and West Germany, had better access to evidence against Waldheim both now and at the time of his U.N. tenure.

"Our knowledge was minor compared to that of the U.S. authorities," said Gavrilovic. "And if none of the great powers wanted to raise the case in the United Nations, what reason was there for Yugoslavia to do it? We were not in a position to use that kind of presssure."

Venceslav Glisic, a historian at a state institute, said that the material added to Yugoslavia's file on Waldheim in 1967 was drawn from copies of German archives made available by the United States. He said the new items included a photograph of Waldheim at a meeting with an Italian general and a German general in 1943 and documents suggesting that he participated in a bloody 1942 offensive in the Kozara Mountains.

Glisic said he was informed of the new evidence at the time of the 1967 review and had "no doubt" that it had been forwarded to the United Nations. He said, however, that Yugoslavia still lacked proof tying Waldheim to crimes.

"There was never any proof in his case," he said. "It was just supposed that he was a war criminal. His role was never clear -- and that is why it was possible for him to hide his background."

Gavrilovic's account of the Waldheim case, issued here last week by Tanjug and endorsed by the Foreign Ministry, said that Yugoslavia identified some 5,000 war criminals in the aftermath of World War II and that 2,700 of these were registered by the U.N. War Crimes Commission, which operated from 1943 to 1948. Only 150 suspects were eventually captured or extradited to Yugoslavia, however, and Waldheim was only one of thousands who remained at large, the report said.

The commentary said that Yugoslavia did not continue to press for the extradition of suspects after 1948 because the onset of the Cold War and Yugoslavia's break with the Soviet Union made such action politically impractical.

The commentary did not address the question of whether top Yugoslav leaders, including Tito, were aware of the charges against Waldheim or discussed them with him during his tenure as foreign minister and U.N. secretary general.

Explanations of Tito's position by top communist officials have been contradictory. Jose Smole, the former president's private secretary, told reporters here last week that Tito, who died in 1980, was unaware of the case against Waldheim.

But Mitja Ribicic, Yugoslavia's prime minister from 1969 to 1971 and now a high communist official, said in an interview with an Austrian paper that he believed Tito knew about the case.

Tito, who commanded the partisan forces that were the target of Waldheim's alleged criminal activity, apparently maintained warm relations with the Austrian. The two met at least 10 times during the 1970s and Tito once awarded Waldheim Yugoslavia's highest decoration for a foreigner, according to press accounts here.

The uncertainty about Tito's role and the government's handling of the case provoked protests from several communist delegates at a party congress in the northeastern republic of Slovenia last week. The delegates and a student organization charged that the official silence was damaging the country's image abroad.

Several officials said, however, that no further explanations -- or action against Waldheim -- were likely to come from the government. "The Yugoslav people are not concerned about this matter," said Gavrilovic, who said his commentary had been issued only "because there was a great deal of international pressure on Yugoslavia.

"For us, it is a minor matter. We have many problems today, and to go back and investigate something that had almost been forgotten is just not worth it."