In the Soviet Bloc, where human rights groups tend to fall early victim to the repression they condemn, Czechoslovakia's Charter 77 is an example of survival against the odds.

Marking the eighth anniversary of its existence recently, Eastern Europe's oldest dissident group issued a lengthy restatement of principles and aims -- in part to remind the world it still exists and in part to clarify for signatories what the movement stands for.

Charter 77's field of comment has broadened since its founding in 1977 in defense of human rights. In recent years, it has produced reports on such diverse topics as pollution, rock music and drugs. Its aim, say supporters, is to offer Czechoslovaks an alternative voice to that of their Communist government.

A lengthy appeal issued by the charter movement this month called for the dissolution of NATO and the Warsaw Pact and the creation of an association of "free and autonomous" European nations. "Perhaps such an ideal seems a dream," said the 17-page document. "Yet we are convinced that it represents the will of most Europeans."

Going up against one of the most stiff-backed regimes in the communist world has been a painful experience for many signers of the charter. A large number have been or are still being prosecuted, and often imprisoned, for participating in the movement.

Most of the signatories have endured a variety of forms of harassment, from loss of jobs to permanent police surveillance to exclusion of their children from universities.

On March 11, the day Mikhail Gorbachev came to power in the Soviet Union, police in Prague raided an apartment where 48 persons, many of them chartists, were viewing newsreels of the 1968 Soviet-led invasion of Czechoslovakia. All were detained, some for as long as two days, then released.

"We offered dialogue to the state at the beginning, without illusions of course," said Eva Kanturkova, a writer, signer of the charter manifesto and one of those present at the clandestine film showing. "But the only dialogue we've had has been with the state security service."

For all the international attention that Charter 77 has generated, it has made little measurable impact inside Czechoslovakia. "They've been more effective in making their point to the outside world than to their fellow citizens," observed a western diplomat in Prague.

In contrast, the Polish Committee for Social Self-Defense, known as KOR, which formed about the same time, laid an educational and organizational network that facilitated the rise in 1980 of the independent Solidarity union movement. KOR eventually dissolved, and some of its members served as elected representatives of Solidarity or senior advisers to it.

But conditions for dissident groups in Czechoslovakia are vastly different from what they were in Poland. Here, the population is still affected by the 1968 Soviet invasion that rolled back Prague's spring of drastic change. The 1970s decade of turmoil and unrest in Poland was a period of political stabilization in Czechoslovakia, characterized by passivity and conformism among the people.

Czechoslovak dissent was never reinforced, as was dissent in Poland, by strong independent protest movements among workers, peasants and students or by the powerful buttress of the Roman Catholic Church -- which is tightly controlled by the Prague government. "Charter has remained a single stream of overt dissent rather than one of several mutually reinforcing currents," concluded Canadian Prof. H. Gordon Skilling in a 1981 study.

Charter 77 insists that it does not aim to be a mass movement. Supporters, known as signatories, number 1,200, and the group has been gaining only several dozen new ones per year. Few in Slovakia have signed; from the start, Charter 77 has been a Czech movement rather than a national one. Some critics regard this as a principal weakness.

"It is not an organization nor a basis for opposition activities," said an anniversary statement issued in January. "Charter 77 has no members, only signatories. It is not something one can join or leave, only sign.

"It does not intend to enunciate its own programs of political or societal changes or reforms. Its goal is the rehabilitation of people as the true subjects of history.

"What a person can gain from signing is the feeling of being liberated, the feeling of being true to himself, the feeling of being publicly responsible again, the feeling of having left the forum of general indifference and of not participating, with his silence, in matters that are evidently immoral."

Charter 77 is represented by three spokesmen who change from year to year. Their names are attached to the documents released irregularly in the group's name. The three used to be chosen to reflect the major factions -- ex-Communists, Roman Catholics and noncommunist intellectuals. This year's all have leftist backgrounds.

How are subjects chosen for charter reports? "There is no bureaucratic approach," explained Jiri Dienstbier, a former journalist and one-time Communist Party member -- now working as a night watchman -- who is a spokesman. "Someone usually comes up with an interesting idea. But that's not enough.

"You need a group of people to do the research. For instance, for five years we tried to prepare a document on ecology but weren't satisfied. We finally published one last year that was written by a commission of government specialists who couldn't get their study published officially."

The example highlighted the help that Charter 77 sometimes receives from establishment insiders. Charter provides them an outlet for information that a Communist censor has blocked. Another such case was a report on health care drafted by doctors working in medical institutions.

"We are not so totally disconnected from society as is sometimes thought," said Dienstbier.