The Soviet Communist Party newspaper Pravda warned today that economic difficulties may lead to the outbreak of a "nationwide conflict" in Poland and that "the deepening of negative and dangerous developments" there threaten Poland's national security.

Pravda gave this gloomy assessment in an account of a meeting in Warsaw yesterday of the Politburo of the Polish Communist Party.

The Pravda account was a departure from the Soviet practice of selecting foreign statements to reflect its own critical views. With the exception of a bitter attack on the U.S. Congress over a resolution on Poland, there have been no statements here in recent weeks to suggest that the situation there was deteriorating.

East European sources here said the Pravda account marks a change in Soviet treatment of news from Poland since the special congress of the Polish Communist Party two weeks ago. Although it did not say so explicity, the article left the impression that the Soviets are disappointed with the drift in Poland and that they see the Polish congress as having failed to produce the expected normalization in the country.

Now the Soviet public is being told that Poland is facing new and even more serious dangers.

Tonight, Moscow television expanded on this theme, and also directly attacked the leaders of Poland's independent trade union federation, Solidarity, for failure to call an end to the current demonstrations in Warsaw.

"Their irreconcilable statements are only heightening tension in the country," the broadcast said.

It added that the current protest was planned to coincide with the opening of negotiations between the government and Solidarity and thus "exert pressure on the government."

The mounting tension in Poland, in now appears, may delay the expected visit here of Polish party leader Stanislaw Kania. He was reportedly scheduled to visit Soviet President Leonid Brezhnev at his Crimean vacation resort this week.

Apart from Bulgaria's Todor Zhivkov, whose daughter died recently, Kania is the only East European leader who has not yet attended the traditional summertime Black Sea consultations with Brezhnev.

There is speculation here that Kania now may come after the Polish Central Committee Meeting scheduled for Saturday. Kania's predecessor, Edward Gierek, spent two weeks on the Black Sea last year, at a time when the workers' unrest in Poland gathered steam to errupt into a virtual revolt.

The Polish situation is believed to have been one of the major topics in Brezhnev's meetings with the leaders of Czechoslovakia, East Germany, Mongolia, Hungary and Romania. There has been no mention of Poland in the official communiques, however, and practically no information has reached here on the course of these discussions.

A communique published this morning on the visit of East German Communist leader Erich Honecker reaffimed the Moscow position indirectly. He and Brezhnev, the document said, agreed that the Warsaw Pact should be strengthened and that "any attempt to subvert" close ties between allied countries "will meet a resolute rebuff."

Diplomatic observers here said that they have detected growing anxiety about the Polish Developments and that the Pravda account may signal a resuption of public Soviet pressure, which had eased two weeks before the Polish congress. Until then, the press here described the situation in ever more threatening terms that culminated in the warning letter Moscow sent to the Polish party in early June.

Tonight, the official news agency Tass in a dispatch from Warsaw said the current situation gives "cause for serious concern to all who hold dear the well-being of Poland and the fate of socialism."

In an account of a meeting of the Warsaw Communist Party organization, Tass said that "the attempts to transfer discontent from factories into the streets" threatens Poland "with chaos anarchy ((and)) is directed against the vital interests of the entire society."