HRADECEK, CZECHOSLOVAKIA -- Two decades ago, when Soviet tanks rumbled into Czechoslovakia, Vaclav Havel rushed to the nearest radio station to denounce the invasion of his country. The streets were full of thousands of young Czechs shouting their contempt for the invaders and chanting their allegiance to the ideals of the Prague Spring.

Twenty years later, society has been "normalized," to use the Orwellian expression of the country's present rulers. The Communist Party has long since purged itself of would-be reformers. But Czechoslovakia's leading playwright is still issuing almost daily blasts of defiance against the invaders and the people he considers their quislings.

This weekend, as the rest of the country marked the 20th anniversary of the Soviet invasion, Havel and fellow members of the Charter 77 human rights movement took the opportunity to denounce once again "the most important military operation since World War II." The invasion, they said, had resulted in a "veritable national catastrophe": the "moral, spiritual, social, political, economic, cultural and ecological destruction" of Czechoslovakia.

Vaclav Havel is a curiosity in Western terms -- a writer who devotes much of his time to politics, the free citizen of an unfree nation. He has been imprisoned three times since the 1968 invasion for a total of five years -- most recently from 1979 to 1983. His plays are performed in London, New York, Paris, but not in Prague. The last time the 51-year-old writer saw one of his own works on stage was 20 years ago.

The only way of understanding Havel is against the background of an intellectual tradition that has its roots in the extinction for 300 years of an independent Czech nation. In 1620, the Czech nobility was decisively defeated by the Hapsburg Empire at the battle of the White Mountain, and 27 ringleaders of an attempted uprising were publicly executed in Prague's old town square.

For the next three centuries, until Czechoslovakia won recognition as an independent state after the First World War, the gorgeous baroque city of Prague was a provincial outpost. Czechs were excluded from the political life of the empire and the official language -- in Prague as in Vienna -- was German. The role of preserving and defending the Czech language and national consciousness fell to the writers.

"In the 19th century, the most important people in our nation were writers," said Havel during a recent conversation in his farmhouse at Hradecek. "Something of this tradition still exists today. A writer here has more functions than a writer in an open society. People have entrusted their hope into our hands. A writer is forced to play a political role, to express the will of society. This is an extra responsibility for writers, but it is also dangerous. A writer has to write the truth, he cannot be an instrument of someone else."

During the summer, like many Czechs, Havel escapes from Prague to his home in the country. He uses the time to catch up on his writing. But even here, amid the rolling hills of Northern Bohemia close to the Polish border, politics is never far away. People call to press a cause. Journalists come asking for interviews. Charter 77 members gather to discuss their latest declaration.

Hradecek turns out to be a difficult place to locate -- the site of a former castle that has ceased to appear on modern maps. But once in the vicinity, finding "Pan Havel" is simplicity itself. Everyone -- from farmers to visiting holiday-makers -- seems to know where he lives. Czechoslovakia's most celebrated dissident comes to the door wearing a T-shirt emblazoned with the words "No Problem."

By Czech standards, Havel lives in relative luxury. The spacious farmhouse, which he bought with his wife Olga in the early '70s, is full of nice furniture and Western video equipment. By the standards of a world-renowned playwright, he lives modestly.

The road to dissent began for Havel in the early 1950s when he was prevented from attending high school because of his family's wealthy background. His literary inspiration came from banned poets like Jaroslav Seifert, who subsequently won the Nobel Prize for literature. In 1956, when he was 20, he unsuccessfully challenged a conference of young writers to recognize Seifert.

By the mid-'60s, the political and cultural atmosphere in Czechoslovakia was beginning to relax. Havel became resident playwright at the Theatre of the Balustrade in Prague, writing and staging his first full-length plays, "The Garden Party" (1963) and "The Memorandum" (1965).

Havel's plays depict situations that seem absurd from the outside but have their own internal logic. "The Memorandum," for example, describes an organization that introduces a new "scientific" language to replace ordinary language. The new language is useless as a means of communication, but is a valuable political weapon in the hands of bureaucrats who want to depose the old "humanistic" managing director.

The "scientific" language, of course, is a metaphor for Marxism -- and the play a thinly disguised description of what happened to Czechoslovakia when the Communists took over the country after World War II. The managing director -- whom Havel modeled on postwar Czech President Eduard Benes -- hopes he can "salvage this and that" if he avoids an "open conflict" with his ruthless deputy.

The Prague Spring was a period of freedom that Havel looks back on as "an unbelievable dream." It was followed by the "normalization" period presided over by Gustav Husak, Alexander Dubcek's successor as first secretary of the Czech Communist Party. Havel considers this period a suspension of Czech history. In a recent essay, he wrote: "It was as if biological time went on as before but social time had stopped."

Charter 77, of which Havel was one of the main inspirers, was in part an attempt to restart history. Signed by 241 people when it first appeared on Jan. 1, 1977, it has now attracted more than 1,500 signatories. The idea was to provide society with a voice, "to straighten up as a human being once more after being humiliated, gagged, lied to and manipulated."

"The moment it emerged," wrote Havel last year, "the interplay of different relationships came alive again. A body that had been thought dead suddenly gave signs of life ... the future was an open book once more."

Since Mikhail Gorbachev came to power in the Soviet Union in early 1985, Czech authorities have eased up on political repression. All but a handful of dissidents have been released from prison. Secret police agents have temporarily dismantled the mobile guard post they set up outside Havel's farmhouse to observe comings and goings.

For Havel, a crucial test of the government's intentions is the official attitude to 1968. So far, he notes, there has been no challenge to the official view that the invasion was justified to save Czechoslovakia from the threat of "counterrevolution."

"Nothing can change in our country without reopening up the theme of 1968, but this is something that is extremely difficult to do for the present leadership. It would be suicide for them. The invasion put them in power. They persecuted all reformists. It would destroy their own identity to speak about these events honestly," he says in halting but understandable English.

Gorbachev's problem, in Havel's view, is that he has thrown in his lot with the present Czech leadership. The Kremlin does not want instability in Eastern Europe at a time when it is dealing with crises as varied as the war in Afghanistan and strikes in Armenia. But unless Gorbachev revises the official Soviet view of the invasion, ordinary Czechs will continue to doubt his sincerity.

"Of course it's better for us that the head of the Soviet empire should be someone like Gorbachev rather than Stalin. But we should be realistic. Gorbachev is limited not only by the conservatives in the Soviet Union, but by the boundaries of his own brain. He speaks about democracy and pluralism, but he believes in a one-party system.

"Our society has an ambivalent attitude toward the reforms going on in the Soviet Union. Of course there is a satisfaction that our occupiers are trying to do what we did in 1968 20 years later. But there is also a wariness about doing these things ourselves because of the persecution that we have been through. The Soviets do not have this experience of persecution in their immediate history. They are more committed, more enthusiastic," Havel said.

Havel, who is still a nonperson as far as the official Czech press is concerned, recently gave an interview to a Soviet youth paper, Komsolmolskaya Pravda. He says that publication of the interview in the paper's weekend section provoked a diplomatic protest from Prague to Moscow.

To describe the shortsightedness of Czechoslovakia's present leaders, Havel used the parable of the missing toilet paper. For months, it has been practically impossible to buy this essential commodity in Czechoslovak shops. Frightened that people might revolt if living standards decline, the government has imported large quantities of toilet paper from abroad -- but it doesn't invest in machines that could produce domestic toilet paper.

"They appreciate the need for toilet paper now, but they don't see the need for toilet paper in five years' time," jokes Havel.

"This cannot go on forever. Something has to change. There is too great a distance between the official ideology and the state of mind of society. I cannot imagine that this relatively modern state, with democratic traditions, in the middle of Europe, can become another Albania."

Havel is aware that his international reputation has helped him resist pressure from the authorities to fall into line. A recurring theme in his work is the dilemma faced by millions of his fellow countrymen: Compromise your principles or risk losing your job.

In his play "Audience," a typical faceless citizen turns on a soft-spoken dissident and shouts: "You always got a chance, but what about me? Who's gonna write about me? Who's gonna help me? Who even gives a {expletive}? I'm just the manure that makes your fancy principles grow."

Havel does not have any answer to this except that, as a writer, he can try to tell the truth as he sees it. He is obsessed with the idea of truth-telling. For him, supporting the ideals of Charter 77 is equivalent to "living in truth" -- being faithful to one's individual principles in a political system that has traditionally been based on the assumption that everyone should think the same way.

In Havel's view, "the truth" is like a life-giving virus that has the ability to eat away and eventually destroy unhealthy social organisms.

"The strength of Charter 77," he said in a recent interview, "is drawn from the truth it articulates, a truth which is on the whole shared by society. The charter does not have the energy and the conditions to put what it says into practice. Nevertheless, the fact that there exists a crucial mirror held up to the times is extremely important. The importance of the mirror's existence far exceeds the importance of the number of people holding it."

Havel's insistence on holding up a mirror to society has turned him into a nonperson in his own country. His name has disappeared from encyclopedias and theater histories. During his last spell in prison, he met a fellow inmate who was once employed cutting out the "Havel" entries in encyclopedias and replacing them with something more edifying.

For a playwright, never seeing your work on stage can be dispiriting. As Havel points out, "A playwright is not like a novelist. His work does not exist until it has been performed on stage."

All these difficulties notwithstanding, Havel appears to have given no thought to emigration. Czechs, he says, do not make good e'migre's. There are, of course, some obvious exceptions: Milan Kundera, Milos Forman, Ivan Lendl. But for Havel, preoccupied as he is with "living in truth," emigration would represent "an escape from truth instead of a journey in search of it."