Two uprisings remembered in Eastern Europe. Only remnants of Prague Spring reform movement and Poland's Solidarity trade union survive today

August is the month of two key anniversaries in Eastern Europe. In Prague, a Warsaw Pact intervention on Aug. 20, 1968, toppled the reform movement of Alexander Dubcek less than eight months after its inception.

And in Warsaw, in August 1980, nationwide strikes forced recognition of the Solidarity trade union and also compelled a change of party leadership at the top.

The East bloc's first-ever genuine and independent trade union survived only a bit longer than the Prague Spring reform movement. In Solidarity's case, there was no invasion or direct intervention from outside. But intense pressure from Moscow and its hard-line allies in East Berlin and Prague was a decisive factor in disposing of the reform movement.

Memories of what might have been had the Dubcek movement been allowed to flourish have faded. Time, and the carrot-and-stick tactics with which the Czechoslovak regime of Gustav Husak pursued its so-called ``normalization'' process, have seen to that.

Only the dissident Charter 77 movement continues as a permanent irritant for the authorities. It remains a source of concern each August. Although the liklihood of open public protest has disappeared with the passing years, the regime still takes no chances.

This year, three leading Charter 77 sponsors were taken into custody and interrogated about the annual anniversary declaration that the group proposed to release.

The document made the group's customary demand for an end to the ``temporary stationing'' of Soviet troops in Czechoslovakia -- using the euphemistic term in the treaty that has ratified their presence in Czechoslovakia since the 1968 invasion -- and an appeal for the government to respect human rights.

The statement was innocuous enough, but it was sufficient to prompt police action against Vaclav Havel, the much-imprisoned playwright; Ladislav Lis, a Dubcek party reformer with a record of some eight arrests for Charter 77 activity; and Jiri Dienstbier, a third former prisoner and one of the group's current spokesmen. [Mr. Havel was detained over the weekend, his second detention in a week, Reuters reported. The news agency said that police appeared to be searching for copies of the anniversary text.]

All three men were released without charges but warned that they might be charged if they pursued their activities at this sensitive period.

Deterrence seems to be the purpose of similar action taken by the Polish authorities against a former regional leader in the now-banned Solidarity trade union.

Marian Jurczyk, who led the 1980 negotiations with the government in the Baltic port of Szczecin, was arrested and interrogated about a Polish anniversary document. It accused the government of failure to uphold the human rights agreed to in 1980, urged Poles at large to reject government policies based on ``coercion and suppression,'' and demanded the return of independent labor unions.

Together with the call made by the militant remnant of the Solidarity underground for a general voter boycott of October's parliamentary elections, any invitiatives taken just now by Solidarity's above-ground activists would likely provoke government response.

Both in Poland and Czechoslovakia the authorities continue to show themselves ready to take tough action against forthright, active dissent. But they seem also now confident enough to keep a low profile in their present watch for anniversary ``subversion''.

There was, for example, a meaningful police presence outside the Gdansk shipyard Aug. 14 when Lech Walesa, with a crowd of several hundred, laid flowers at the monument to the victims of police shooting in the food-price protests of 1970. But there was no interference.

The authorities in Prague and Warsaw are much more preoccupied with gripping economic troubles than with such opposition as there is.

In Czechoslovakia, lingering protest over 1968 was largely cooled by the consumer-oriented policy that the regime of Gustav Husak followed after its takeover in 1969 through the late 1970s.

In that period Czechoslovakia enjoyed some of the highest living standards within the East bloc. But those standards -- though still better than most -- have slipped as the economy has stagnated.

Still, Czechoslovakia is not burdened, as are Poland and Romania, with big debts from Western borrowing. But its doors have also been shut to diversification and Western technology. And its economy has become so enmeshed within Comecon, the Soviet trading bloc, that almost 50 percent of its trade is tied to the Soviet Union and 75 percent to the East bloc as a whole.

In Poland August memories are even fresher. But the public will to go on actively identifying with protest has been eroded by years of day-to-day economic hardship.

The government newspaper Rzeczpospolita has laid some of the blame for government failures on the trade unions that the authorities set up to supplant Solidarity. The unions, it said, were not behaving like the partners they were intended to be and had neither curbed excessive pay demands nor applied themselves to increasing productivity and work discipline.

``Unforunately,'' says Col. Stanislaw Kwiatkowski, head of the government's public-opinion center, ``our propaganda is incapable of convincing people.''