In the old interrogation technique, the captive is questioned by two men alternately. One plays the tough guy, brutal and uncompromising. The other is relatively sympathetic.

For the past year, since the eruption of the Polish crisis, neighboring Czechoslovakia has taken the role of the tough interrogator, giving the Soviet Union a chance to seem less harsh. Through the speeches of its leaders and comments in the officially controlled media, Prague has conducted an unremitting propaganda campaign against Poland's independent trade unions and "revisionists" in the Communist Party.

By comparison, even the Kremlin's blasts have seemed mild. The tough-soft approach was perfected at the Czechoslovak Communist Party congress in April, when the Czechoslovak leader, Gustav Husak, spoke menacingly of the duty of all communist countries to save Poland. The next day it was left to Soviet President Leonid Brezhnev to relax the psychological tension a little by expressing confidence that Polish Communists could manage by themselves.

During the recent strikes in Poland over food shortages, Prague was once again on the attack. Almost daily reports appeared in the press about the worsening food shortages in Poland, speculation and corruption and the failure of the Polish party to resolve the crisis.

Zdenek Porybny, acting foreign editor of the Czechoslovak Communist Party newspaper, Rude Pravo, denies that Czechoslovakia is leading an anti-Polish campaign. But, in an interview, he agreed that the Czechoslovak press devotes more extensive coverage to Polish affairs than other Soviet Bloc news media.

"We let the facts speak for themselves," he said.

Western diplomats here are convinced that all comment on Poland is closely coordinated with Moscow. It is not as if the Czechoslovaks are speaking out of turn. All the same, for historical and political reasons, the Prague leadership appears to relish its assigned role.

These diplomats say the principal reason for the hard-line reaction on Poland is psychological fear of contamination. In the short term, this would hardly appear justified since as long as the Polish experiment is associated with empty food stores it is unlikely to appeal to ordinary Czechs and Slovaks who are accustomed to relatively high living standards.

The long-term outlook could be very different, however, particularly if Poland is successful with economic reforms.

For the time being, the thrust of Czechoslovak propaganda is that nothing good can come out of the Polish reform movement. Czechoslovak journalists have adopted an "I told you so" tone, putting the blame for Poland's economic crisis on the "political ambitions" of the leaders of the independent trade union federation Solidarity and the "weakness" of Polish authorities.

One reason suggested by Porybny of Rude Pravo for Czechoslovakia's outspokenness on Poland is its own experience in 1968. In the official Czechoslovak version, the liberalization movement known as "the Prague Spring" represented a grave crisis that was gradually resolved thanks to Soviet intervention and "a normalization process" during which hundreds of thousands of reformers were ruthlessly purged.

According to this analysis, repeated by Porybny, Czechoslovakia is now particularly well-placed to give advice to Poland on how to deal with the threat of counterrevolution. An additional twist is that Poland participated in the 1968 invasion, so Prague is only repaying the "fraternal assistance" it received then.

A second reason is that Czechoslovakia's own economy has suffered as a result of Poland's failure to meet contractual obligations for coal and other raw materials. Several Czechoslovak factories have claimed production losses as a result. But Czechoslovak officials refuse to give an exact figure for the shortfall in supplies and it is not clear to what extent Poland is being used as a whipping boy for domestic economic difficulties.

Porybny claims that last month's Polish Communist Party congress solved nothing.

"There's a new leadership and a new Central Committee, but now we're seeing street demonstrations," he said. "The crisis continues and the economic situation is catastrophic. The counterrevolutionaries are strengthening their positions. From the authorities, we hear only words . . . nothing but words."

The implication of Porybny's remarks is that eventually the Polish experiment will collapse on its own. So desperate will the economic problems become that Solidarity will lose popular support. There will then be a three- to five-year "normalization" process on the Czechoslovak model in which the Polish party reasserts traditional controls over society.

In the meantime, the Czechoslovak leadership is taking no chances. A crackdown on dissidents, notably members of the Charter 77 human rights movement, is in progress. Three weeks ago, a Prague court sentenced former Charter spokesman Rudolf Battek to 71/2 years in prison on subversion charges, a particularly harsh sentence even by Czechoslovak standards.

In addition, another 16 or so dissidents including former foreign minister Jiri Hajek are under investigation for alleged antistate activities. Further heavy sentences could damage several Czechoslovak foreign policy interests, including a planned visit by President Husak to neighboring Austria and a successful conclusion to long-running negotiations on repatriation of Czechoslovak gold by the United States.

On the economic front, Polish developments appear to have strangled the prospect for any major reforms in Czechoslovakia. A Western diplomat commented, "With so much uncertainty elsewhere in Eastern Europe, this is not the time for rocking the boat here."

The consequence, political analysts agree, has been to strengthen the already dominant ideologues in the Czechoslovak leadership at the expense of technocrats. At a Central Committee meeting in October, even modest and economically justified price increases were delayed.