The trial and lengthy jail sentence handed out last month to six human rights activists by the communist government of Czechoslovakia are causing more trouble for governments in more liberal Soviet bloc countries where embarrassing displays of support for the imprisoned Czechoslovaks are spreading.

In Hungary, more than 250 intellectuals, sociologists and cultural figures have signed a series of letters not only to their "friends" in Prague jails but also to Hungarian Communist chief Janos Kadar, calling on him to use his influence to help the prisoners.

The situation, according to informed Hungarian sources, has created "a deep embarrassment and dilemma" for Kadar, who is widely respected in Hungary for his skill at avoiding sharp confrontations within the Soviet Bloc that could threaten his country's relative liberalism.

These sources say there are indications that a number of Hungarian Communist Party officials, possibly including Kadar, believe Prague's actions were "wrong, foolish and primitive," smacking of Stalin-era techniques at a time when several governments are under growing economic pressures and need public support. They say the Czechoslovaks are pressing the Kadar government to crack down on those who signed the petitions of support.

Kadar, however, is viewed as not likely to crack down, at least in any way that might provoke domestic stains. Hungarian sources point out, however, that the number of Hungarian personalities signing the petitions is more than seven times as high as the 34 intellectuals who risked signing an open statement two years ago when the Czechoslavak human rights group first published its famous "Charter 77."

Kadar's dilemma is that where once there were only 34, there are now 254 signers. And if he doesn't punish them, there will be 500 the next time. "There are a lot of people around who were afraid to sign the first time. Now they'll be less afraid," one Hungarian source said.

Kadar also has embarked on a major new economic reform program and has raised prices sharply to help finance it. In March, a crucial party congress will be held and party hardliners may try to use the display of dissent to derail the party chief's liberal economic philosophy.

In neighboring Poland, where there are a number of organized dissident groups in contact to the scattering of individual critics in Hungary, the trials also produced open student demonstrations and intellectual protests by small groups.

Last week, however, an unusual and possibly more significant display of weekly "tysodnik Powszechny" published an article by a prominent Czechoslovak Catholic theologian who signed the 1977 charter and who has not been able to have his work published in his own country for eight years.

Although the article was about Pope John Paul II and not the Prague trials, the publication is viewed as significant because the paper always is censored heavily by the Polish government. Thus the government, by allowing the article's publication, may also be expressing indirectly its dismay over Prague's actions.

Warsaw's other state-controlled papers have published only a brief mention of the jail sentences, another sign that may reflect government embarrassment over Prague's actions.

Adding to the tension among people outside government here, and probably in Warsaw as well, is uncertainty about the role of Moscow in the Czechoslovak actions.

Some sources believe the Czechoslovaks would not have embarked on a controversial trial without Moscow's backing.

This week, the Soviet party newspaper Pravda came to Prague's support, sharply rebuking West European Communist parties that have criticized Prague. Pravda called the Czechoslovak dissidents "renegades" who were allied with subversive forces and supplied false information to outsiders.

In this view, the Kremlin wants to warn its allies to keep a tight rein on dissidence as next year's Moscow Olympics and the Madrid conference to review the Helsinki agreements approach.

There are others, however, who believe the Kremlin rebuke is perfunctory and that Prague may well have blundered, as many in the Soviet Bloc feel it did two years ago when its reaction to the publication of the Charter 77 manifesto called more attention to it then might have otherwise been the case.

In Hungary, the issue is especially sensitive.

The 1977 petition here supporting the Czechoslovak charter was aimed only at Prague. The new series of letters, however, also involves the Hungarian government and raises other touchy issues, including Hungarian responsibilities to help protect the human rights of 600,000 ethnic Hungarians in Czechoslovakia.

The letters also emphasize that Hungary took part in the Soviet-ordered Warsaw Pact invasion of Czechoslovakia in 1968 to crush a liberalism that briefly flowered in Prague.

"We are Hungarians," one letter said, "citizens of a state that participated in the occupation of Czechoslovakia and therefore we feel a special responsibility for all that has been happening there since 1968."

The open letter to the Czechoslovak prisoners even raises doubts about the basic Hungarian approach to life within the Soviet Bloc since Hungary's own violent but short-lived uprising in 1956.

That approach is identified with Kadar, 67, for the party chief who has run Hungary for the past 23 years. Kadar has coupled allegiance to Moscow on foreign policy matters with gradually increased flexibility on domestic matters, a policy that has given his country the most Western-style economy and relaxed travel restrictions in the East.

Kadar's political skills are genuinely respected in the West and East, yet many thoughtful Hungarians are worried about what will happen after he is gone, another factor adding to tensions over the Czechoslovak situation.

"There is a whole generation of us," as one Hungarian writer said "whose entire adult life has been spent under Kadar."

In the open letter to Prague, however, the Hungarian authors -- two philosophers and a former editor -- wrote that "the violent liquidation of the Czechoslovakian experiment in 1968 taught us, just as it taught others in surrounding countries, that democracy in Eastern Europe can only be achieved through cooperation of peoples belonging to the area."

"But we have to confess," they wrote, "that at the time of the invasion it was only a small minority who understood this in Hungary. The majority reasoned that democracy for us was no more than a vain hope . . . The situation, so the reasoning went, can at most be improved step by step, within the framework of the existing political system. What is more, it was thought advisable to increasingly isolate ourselves so that our survivors remain unnoticed by our suspicious neighbors."

For a long time, the authors said, the majority view seemed right. The standard of living improved and state control over cultrural life became more flexible.

Yet, they conclude, "the limits of such an evolution gradually become apparent . . . And the more we use up the possibilities of the evolution the more people there are who are not satisfied with the diminishing results. There are more and more people in Hungary who don't want to give up hope of democracy for such a small price."