PRAGUE, Czechoslovakia -- The Communist Party of Czechoslovakia and its government were in full retreat Sunday on the eve of a planned two-hour general strike that promised to be the single biggest test of strength yet between the beleaguered authorities and an opposition that seems to grow by the hour.
It followed another whirlwind day of political turmoil that included:
-- The second purge of hard-liners from the Politburo in three days.
-- The first substantive talks between the Communist regime and the umbrella opposition group, the Civic Forum.
-- The revolt of key party committees in Prague and Slovakia.
-- The extraordinary spectacle of a senior Communist leader being jeered by an assembly of half a million of his compatriots.
In the face of tremendous public pressure, three of the best-known hard-liners were dropped from the Politburo, including Prague party boss Miroslav Stepan and trade union chief Miroslav Zavadil.
The party's senior foreign affairs specialist, Jozef Lenart, was also dropped.
The most significant of seven elevations, which included two women, to the senior policy-making body was that of 37-year-old Vasil Mohorita, head of the party's youth wing. Mohorita is believed by diplomats here to have reformist tendencies.
A source close to the party's Central Committee also spoke of a proposal to drop one-fifth of the Central Committee's conservative membership and replace them with Communist members of strike committees. The fate of the proposal was unknown.
Only hours earlier, the country's Communist prime minister, Ladislav Adamec, met with a delegation from the Civic Forum.
"Dialogue with the powers that be has begun," playwright and Civic Forum leader Vaclav Havel told an outdoor rally officially estimated at 500,000 people on a frozen Prague parade ground Sunday.
"From this moment, we shall all participate in the management of this country, and all of us bear responsibility for its fate," the popular dissident added.
Havel's historic handshake with Adamec was broadcast live on state television, which has become an important engine of change in the last few days.
And later, Communist Party chief Karel Urbanek told the second emergency Central Committee meeting in three days that "dialogue with (Civic Forum) is both possible and necessary."
It was a remarkable turnaround for the party, which only days ago clung to its exclusive prerogative of power and called the opposition an anti-socialist threat to the country. But Urbanek said dialogue is now "the only way out of today's taut situation."
The one-hour meeting between Adamec and Havel was described as "intensive" but inconclusive, and a second session was scheduled for Tuesday. At that meeting, the Civic Forum is expected to submit a seven-point reform program that was described at a Sunday evening news conference as intended to build a new democratic, pluralistic Czechoslovakia that would "strive for an honorable place in Europe."
Spokesman Jiri Dienstbier told reporters that the group wishes the country to participate in the process of European integration but that it should "fully respect existing international obligations and commitments."
He said that although the Civic Forum advocates a Europe without defense alliances, the group would not advocate any unilateral withdrawal from the Warsaw Pact.
"Our point of departure is that the structure of Europe is what it is," said Dienstbier. "In this sense, we want to respect agreements as they are. From today, we are trying to make the transition from only criticizing to making our own programs."
As the opposition was presenting a program for the future, the ruling Communists were attempting to salvage something from the present.
Further illustrating the Communist turmoil, the regional party committee in Slovakia resolved at an extraordinary session Sunday that authorities should "re-evaluate the causes of social-political crises, especially in 1968, as an attempt at social reform and renewal of socialism."
The call openly challenges the still-official characterization of the 1968 Soviet-led Warsaw Pact invasion as a necessary response to counterrevolution. It also cuts the ideological legs out from under an entire generation of Czechoslovak party leaders who took over under Moscow's guidance after the ill-fated "Prague Spring" reform movement was crushed.
The newly purged Prague city party committee joined in the chorus of condemnation, saying that "the people of Czechoslovakia have been wiser than their leadership."
The Prague committee also supported negotiations with the Civic Forum and demanded democratic elections to choose delegates for an emergency party congress to draft a new "action program."
Party chief Urbanek proposed that such a congress be held Jan. 26.
Addressing Sunday's massive rally in Prague--which state television reported was one of at least 11 held in every major city in the country--Havel said, "Civic Forum wants to be a bridge from totalitarianism to democracy and true political pluralism, which ultimately will ensure free elections."
Also on a makeshift stage overlooking Prague's giant Letna parade ground was Alexander Dubcek, former Communist Party leader and inspiration of the 1968 reform movement who was exiled in disgrace after the Soviet-led invasion. It was the 68-year-old reformer's third public appearance here in as many days after more than 20 years of political oblivion.
In one of the most emotional, poignant moments of what has been an extraordinary week, a junior officer of the state People's Police apologized at the rally for systematically and brutally beating students last Nov. 17 as they protested peacefully for an end to repression.
The viciousness of the police that night served as the match that ignited a firestorm of dissent that in less than 10 days has brought the Communist hard-line regime to the brink of collapse.
Standing ramrod straight, his face filled with emotion, the young police lieutenant told the crowd: "I want to profess my profound apologies that our leadership set us against the people of our own country.
"We members of the (police) support democratic change taking place," the young police lieutenant, Ludwig Pinc, told the crowd. "The tragedy is that we were the tool to prevent these democratic changes.
"We have to take our share of the responsibility, but we are subordinate to the military and state command," he added. "A policeman is threatened with long prison sentences, especially if he refuses to obey orders during a mass intervention.
"I don't want to say all policemen have the same views, but we cannot all be thrown into the same box."
After the officer completed his statement, the crowd chanted, "Come join us!"
In its own way, the encounter captured both the drama and the immensity of the change that has taken place in Czechoslovakia in just over one week.
The state prosecutor, Jaroslav Kruppauer, informed the student strike committee Sunday that three members of the riot police units on duty Nov. 17 had been formally charged in connection with the violence.