Presidents Vaclav Havel of Czechoslovakia and Richard von Weizsacker of West Germany met with President Kurt Waldheim of Austria today, further eroding efforts over the last four years to isolate Mr. Waldheim diplomatically because of his war record.

Mr. Havel, a longtime human-rights campaigner, has been widely criticized for accepting an invitation to open the Salzburg Festival. But he made his address a pointed lecture to those who ''rewrite their own history'' and ''fear facing their own past.''

Public Contact Minimized

The two visitors minimized their public contact with Mr. Waldheim, who is suspected of having been aware of war crimes committed by his German unit when he was a lieutenant in occupied Greece and Yugoslavia. He also has been accused of having covered up that part of his biography during his rise to high office. Mr. Waldheim served two terms as Secretary General of the United Nations, and it was only during his campaign for the Austrian presidency in 1986 that public allegations about his record surfaced.

In a television interview tonight, Mr. Waldheim said he saw no link between Mr. Havel's statements and his own history. He said he had not rewritten his biography or denied anything from his past, and that ''international commissions'' had ruled that he shared in no guilt for war crimes.

Until today, the only European head of state to have seen President Waldheim in Austria was President George Vassiliou of Cyprus. But in this same period Mr. Waldheim was visited by Pope John Paul II; Giulio Andreotti, Italy's Foreign Minister; Eduard A. Shevardnadze, the Soviet Foreign Minister, and Crown Prince Raja Vajiralongkorn of Thailand.

On his travels in this period, mostly to Islamic countries, Mr. Waldheim has met with King Hussein of Jordan and President Kenan Evren of Turkey.

In an interview published in Vienna on the eve of his visit, Mr. Havel questioned the moral value of Western leaders' avoidance of contacts with Mr. Waldheim.

''I don't want to say that this posture didn't originally have an ethical basis,'' Mr. Havel said in the interview with the daily Salzburger Nachrichten. ''Of course it did, but by turning it into a ritual it becomes void and loses its original moral content and become a cliche.''

In comments reported by the Czechoslovak press agency, Mr. Havel said his decision to attend the festival was a ''expression of respect for the Salzburg festival and especially the Austrian nation.''

Mr. Havel was criticized for coming here even by Charter 77, the human-rights organization that he helped to found and that became the core of the dissident movement under his country's Communist former leadership. His visit was also questioned in a front-page open letter by Lidove Noviny, a daily that is close to the Czechoslovak President. #3 Are Guests at Lunch The crush of photographers and reporters around Mr. Waldheim as he awaited the joint arrival of the visiting Presidents in the Festival Theatre lobby this morning was so great that it apparently prevented his greeting them formally in public.

But the three spoke briefly after Mr. Havel's address and were guests at a lunch given by the province's Governor in a hotel a few yards down the narrow street from the house where Mozart was born.

Lunching with Mr. Havel could not have been easy for the 71-year-old Mr. Waldheim. The literary indirection of Mr. Havel's speech could hardly disguise to whom it was addressed.

Making existential fear of history in Central Europe his theme, Mr. Havel, who is 53, said he had felt such anxiety himself. He spoke of his ''hangover'' in recent days, when the ''poetry'' of the events that made him President gave way to everyday ''prose'' after his election last month by the first freely chosen Parliament in four decades.

''Fear of history in these parts is not only fear of the future but also fear of the past,'' Mr. Havel said. ''He who fears what is to come usually also fears facing what has already been. And he who fears facing his own past must necessarily fear what lies before him.''

''Too often in this corner of the world, fear of one lie leads only to another lie, in the vain hope that it will cover up not only the first but also the very practice of lying,'' he continued. ''But lying can never save us from the lie. Falsifiers of history do not safeguard freedom but imperil it.

''The assumption that one can with impunity navigate through history and rewrite one's own biography belongs to the traditional Central European delusions.

''If some one tries to do this, he harms himself and his fellow citizens. For there is no full freedom there where freedom is not given to the full truth. In this or other ways, many here have made themselves guilty. Yet we cannot be forgiven, and in our souls peace cannot reign, as long as we do not at least admit our guilt. Confession liberates.''

''I have many reasons for the statement that the truth liberates man from fear,'' Mr. Havel said. He said that dissidents in Eastern Europe retained their human qualities only by speaking the truth without fear. ''Otherwise they would probably have succumbed to their despair,'' said the man who served more than four years in prison for speaking his mind.

Mr. Havel concluded: ''Let us try then to free this sorely tested region not only from its fear of the lie but also of its fear of the truth. Let us at last look sincerely, calmly and attentively into our own faces, into our past, present and future. We will reach beyond its ambiguity only when we understand it.''

Visits Are Labeled Private

The presidential visits were labeled private and devoted to the festival, and no national flags bedecked the town, which was bathed in sunshine. Mr. Havel and Mr. Weizsacker, left for home after lunch, the German by helicopter and the Czechoslovak by car.

Mr. Waldheim arrived at the restaurant in his own car, followed minutes later by the two visitors traveling together. In the discussion before lunch, Mr. Havel invited Mr. Waldheim and the Austrian Chancellor, Franz Vranitzky, to send experts to take part in Czechoslovak studies on the safety of a planned nuclear-power plant near the Austrian border that is opposed by Austrian environmentalists.

Mr. Havel explained in his speech that he had accepted the invitation about a year ago in the belief that, as usual, he would not be allowed to travel and would smuggle out his essay to be read by another. Before his first election as President last December, he had not left Czechoslovakia since 1968.

Privately, Czechoslovak officials said earlier in Prague that the President would have avoided the visit had he been invited immediately after the revolution that catapulted him from dissidence to the presidency. He was reported to have sweetened the pill by obtaining Mr. Weizsacker's agreement to accompany him.

The German President, who is 70, had won wide acclaim for a speech in 1985 accepting German responsibility for the crimes of Nazis and had been the first foreign leader whom Mr. Havel invited to Prague after becoming President. Mr. Weizsacker's father, a German diplomat, was convicted of war crimes at the Nuremberg trials, and served two years of a seven-year sentence.

Mr. Weizsacker and Mr. Havel arrived from Germany in a West German Border Police helicopter. Even Czechoslovaks who opposed the visit do not suspect Mr. Havel of having kept the engagement with the Salzburg Festival to ingratiate himself or his nation with their neighbor. His address was clearly not designed to make the Austrian President his friend.

'I Like to Keep Promises'

''I accepted, and I like to keep my promises,'' Mr. Havel said to an Austrian television interviewer.

The only disorder was provoked by two militant American Jews in the theater lobby before Mr. Havel's address, who shouted at Mr. Waldheim, accusing him of mass murder. Austrian reporters identified them as Rabbi Avi Weiss of the Hebrew Institute of Riverdale, the Bronx, and Jacob Davidson. They were taken into custody, a police spokesman said, and released about 90 minutes later on bail of an undisclosed amount. last subhed can bite

Photo: Presidents Vaclav Havel of Czechoslovakia, right, and Richard von Weizsacker of West Germany, center, met yesterday in Salzburg with President Kurt Waldheim despite a tacit boycott of Austria by other leaders. (Agence France-Presse)