Czech leaders dig in to block Soviet-style reform. Twenty years ago Soviet tanks rolled into Prague and crushed a reform movement. Today, Czech activists are finding an unexpected ally in a new reform bid - the current Soviet leader.

When a theater company here called ``Theater on a String'' wanted to put on a series of plays by contemporary Soviet authors, hard-line censors banned the production. The angry theater directors went to the Soviet Consulate and complained. Not long afterward, the controversial plays were performed.

``The Soviet Union has become such a positive element,'' beams Jiri Muller, an activist from the Charter 77 human rights group, recounting the anecdote. ``We use it as an example and a reference.''

Twenty years after Warsaw Pact armies invaded on Aug. 20, 1968, a stunning role reversal has taken place in Czechoslovakia.

Back then, hard-line Soviets crushed reform-minded Czechs. Today, reform-minded Soviets are challenging conservative Czech leaders. One official whispers in private about how he recently traveled to Moscow in order to warn Soviet leader Mikhail Gorbachev.

``We told him to `be careful,''' the official says. ``He should learn from the lessons of the past and not put us in an impossible situation.''

More than anywhere else in the Soviet bloc, the present Prague rulers are associated with the rigid political control and chilling central planning of late Soviet leader Leonid Brezhnev, policies now out of favor in the Kremlin. No wonder they fear that Gorbachev-style reform could destabilize them.

``Our officials always have been saying, `The Soviet Union is our model, our eternal friend,''' adds Jaroslaw Jiru, a journalist at Radio Prague in 1968, who now works as a manual laborer in a printing plant. ``Today, they have to say that we are different, that we have our own past, and special conditions to socialism.''

Using this argument, the Czechoslovak communists have laced their own version of glasnost (openness) with half steps and hesitations.

In recent months, some tough films have been released exploring such sensitive subjects as the spread of drug addiction, the thriving currency black market, and the explosive pollution problem. Works by banned authors such as Franz Kafka and Bohumil Hrabal are again being printed.

But party members purged after 1968 are still considered non-persons, and the Communist Party daily Rude Pravo continues to publish vitriolic attacks against them. The official press offers little coverage of events in the Soviet Union, and Czechs say Soviet television, which is visible throughout the country, is much more daring than their own channels.

``It's what I would call `easy glasnost,''' says journalist Jiru. ``They've opened up on some social problems without opening up on the really important things as in the Soviet Union.''

So far, Mr. Gorbachev seems to have accepted this ``easy glasnost.'' The dominant opinion here in Prague is that the dynamic Soviet leader is preoccupied by his internal affairs, and not strong enough to take on his own conservatives over Eastern Europe. He wants stability in the East bloc.

``Gorbachev needs some time,'' says Peter Uhl, a leading dissident. ``He isn't ready to force changes here which could prove destabilizing.''

Unlike in Hungary, where Karoly Grosz and a new generation of reform-minded leaders recently ousted aging Janos Kadar, the Czechoslovak party has no rising young leaders. The radical reform wing was wiped out in the 1969-70 purges, and it has never recovered.

In the first top-level shake-up since 1969, Milos Jakes, 65, last December replaced ailing Gustav Husak, 75, as a party leader. Mr. Jakes bitterly opposed the ``Prague spring'' reformers and played a key part in the post-invasion purge that swept half a million people out of the party.

``The only ones left in the leadership are old crabs,'' a Western diplomat remarks. ``There are no dynamic Gorbachevs ready to take over.''

A stocky, gray apparatchik, Jakes does not resemble the ebullient, charismatic Soviet leader. Since taking over, the new Czechoslovak leader has given lip service to glasnost and perestroika (restructuring), without convincing anybody of his sincerity. A blueprint for giving companies more independence from the central plan was released in July.

With understandable cynicism, many Czechoslovaks have taken to joking about Jakes's constant pronouncements about the need for economic change. They also exchange quips comparing their leader unfavorably to the national hero Schweik from Jaroslav Hasek's book ``The Good Soldier Svejk,'' about an army private in World War I who finagles his way around the harshness of military life.

``Jakes ends with `s,' Shweik begins with `s,''' the joke goes. ``Schweik is clever and plays dumb. Jakes is dumb and plays clever.''

In contrast, no one seems to know a nasty joke about Gorbachev. For long-suffering dissidents, the Soviet leader represents a glimmer of sunshine on a long-cloudy horizon. Piles of Soviet newspapers can be found in their apartments. The Soviet Communist Party daily, Pravda, used to go unsold in kiosks. Copies are now sold out early in the morning.

``Gorbachev has opened up a new climate here,'' says Jaroslaw Sabata, an ardent Charter 77 Russophile. ``He is destroying the old atmosphere of fear.''

As evidence, Mr. Sabata and other dissidents point to the the growing number of independent associations. Charter 77 is no longer the sole voice of dissent. Then, this year, 500,000 people signed a petition calling for greater religious freedom. Underground publishing is booming. A budding ecological movement is forming.

``The evolution goes quickly,'' says an optimistic Sabata. ``We're all becoming Gorbachevites!''

Next: Czechoslovakia discovers perestroika.