For a small but increasingly vocal group in Czechoslovakia, the anniversary of the Soviet invasion is a bitter reminder of what might have been. One group is Charter 77, named after the Czechoslovak human rights manifesto of January 1977. Ladislav Lis, a founding member, is Czechoslovakia's latest ''prisoner of conscience.''
Twice in the 1970s, Dr. Lis was imprisoned without trial. The second time was for six months. Released in January 1980, he at once resumed activity as a Charter 77 public spokesmen and remained so until arrested last January.
On July 21, he was given 14 months in jail on charges of ''incitement against the regime'' and of distributing ''illegal (Charter) literature.'' The court ordered rigorous police surveillance for three years when he comes out of prison.
When Czech President Gustav Husak began ''normalization'' in 1969, he pledged there would be none of the horror trials of the Stalinist era.
On that count, he was as good as his word. There have been no ''show trials'' of that gruesome caliber. Bkt there have been two periods in which many people were brought before the courts for political activity, which in numerous cases, like Dr. Lis's, was no more than standing up for ordinary civil liberties.
The first, in 1972, involved a group of prominent veteran Communist Party functionaries who refused to endorse the Husak line that Soviet intervention was justified by the threat of counterrevolution. They got sentences of up to 61/2 years, but were freed at the end of 1976 following prolonged Western pressures based on the Helsinki declaration on human rights.
The second wave of trials began after the January 1977 Charter, and included the likes of Lis and sociologist Rudolf Battek, who was given a 71/2-year sentence two years ago.
Monitoring just how many trials have taken place has been tricky because only cases involving well known people - writers, journalists, actors - get published by the Prague press.
The most reliable sources say, however, these trials may have involved several hundred people in total. But provincial proceedings against ''unknowns, '' which rarely get into the central press, are thought to number up to 2,000.
This year, however, there seem to have been fewer dissident arrests. Charter 77 seems to worry the authorities less than another group - the ''underground'' church, maintained by priests and laymen under official ban. Hundreds are harassed short of imprisonment. Currently, ''several dozen'' are reported to be under detention or serving sentences.
Intense propaganda has been aimed at the Roman Catholic Church and at the Pope for conducting a campaign against communist countries where there is a strong Catholic following - most notably, Poland, but also Czechoslovakia and Hungary. Moreover, numerous Catholic clerics and friars have been severely prosecuted.