Outwardly calm and tightly controlled as always, the Soviet capital this weekend seems more deeply worried about a possible Kremlin intervention in Poland than at any time since the crisis erupted there in August.

No government officials can be asked under any terms of confidentiality what the Kremlin's plans for Poland may be, for only the highest councils of the party know, and they are not saying. Even West German Foreign Minister Hans-Dietrich Genscher, who ended two days of talks with Kremlin leaders last night, reportedly could get no answer from either President Leonid Brezhnev or Foreign Minister Andrei Gromyko when he sought to discuss Poland.

Amid the heightened anxiety detectable here, it was speculated today that Polish Communist Party leader Stanislaw Kania and Premier Wojciech Jaruzelski may soon go to Prague for a Czechoslovak Communist Party congress and a possible Warsaw Pact summit meeting.

It is impossible to prove or disprove these rumors, but unannounced movements of party leaders under pressure have occurred before during the peaks of the crisis. Most notably, the entire East Bloc leadership suddenly surfaced here early in December for a summit at which the Poles seemed to gain new support from Moscow even as the Soviet military command was abruptly raising the preparedness of its frontier units.

A number of factors have converged in recent days that have given real jitters to Soviet and foreign sources. These include U.S. warnings about Soviet preparations for a military intervention, a better sense now of the disarray within the Polish Communist Party following the threatened general strike last week, and the impact on people's psychology of the ceaseless denunciations of Solidarity and stiff implied criticism of the Polish leadership by the official Soviet media.

Moreover, East European diplomats had easily dismissed Washington's previous warning of intervention preparations as either disinformation or deliberate attempts to stir the pot. Now diplomats and journalists from these sensitive buffer nations show by their perturbed frowns and hesitant answers that the "clouds," as one put it, "seem much darker than before."

These diplomats see the prospective free elections for a Polish Communist Party congress next July as a watershed. They perceive clear reasons why Moscow would be more tempted than ever, despite warnings of calamitous results for international relations, to intervene now to eliminate the possibility that the elections could alter the Polish party in a massive way that could change the face of socialism in Eastern Europe.

As one source said in a characteristic comment, "The leaders here are old and like elderly people perhaps everywhere, they do not want change. They are opposed to it." In this man's view, the Kremlin has been stretched nearly to the limit of its ability to accept the changes wrought in Poland during the months of crisis. He suggests that Moscow may not be able to swallow so large an indictment of the old way if an election, as seems likely, gives genuine footing to reformers and moderates inside the party.

The shift of Soviet media in the last three weeks to describing Poland as caught in an open struggle for power between "antisocialist forces" and the party has added its weight to this feeling. The party newspaper Pravda noted today, in an expanded version of a Tass dispatch from Warsaw yesterday, that Polish Politburo member Andrzej Zabinski had told a party meeting at a mine that "despite the calm that has set in, the situation has not improved, but even worsened. A struggle for power is now going on in the country."

The media has found Kania's leadership wanting in dealing with the unions. Yet Kania, who was shown on Soviet television last night giving a speech, has assured Moscow that the party has the strength and will to master its fate. The implied rebuff has been stated in too many ways and too many times to be disregarded as mere propaganda, in the view of many foreign diplomats here.

At the same time, there are voices who argue that the Soviets even now are no more disposed to intervening than they were at what is thought to have been one of the moments of Poland's maximum vulnerability, last August, when Soviet reserves were hurriedly mobilized and added to border units in preparation for use of military force.