The Soviet pledged today to defer all Polish debts until 1986 and to provide the country with emergency supplies of food and additional aid in an effort to shore up the embattled government of Communist Party leader Stanislaw Kania.

Kania and the Polish premier, Gen. Wojciech Jarazelski, is turn asserted that their primary duty will be to revive Poland's economy, to put "a check to manifestation of anarchy," and to "fight decisively against counterrevolutionary dangers."

Today's joint Soviet-Polish communique, issued after the two leaders' talks with Soviet President Leonid Brezhnev at his Black Sea resort yesterday, specifically mentioned "the strikes and demonstrations" here during the last few weeks and unspecified "anti-Soviet" activities as creating "serious perils for the security of Poland."

As if to demonstrate the Polish party's increasingly tough attitude at home, authorities today prevented a branch of the independent trade union movement Solidarity from publishing a magazine. Authorities in the industrial town of Nova Huta seized the periodical's equipment. It was unclear whether the branch qould be prosecuted on charges of "anti-Soviet activities."

Also today, the government announced figures for Poland's industrial performance during the first half of this year that show steady deterioration in several key industries.

Poland's overall industrial production declined by 17.2 percent compared to the same period of last year, with coal down by 21 percent, machine tools by 36 percent and car production 26 percent compared to the 1980 statistics.

Missing from tonight's communique, which was made public hours after Kania and Jaruzelski returned home, were expressions of Soviet confidence.

Instead, the communique quoted Brezhnev as saying that the Soviet Union "watches attentively and in all earnestness the course of developments in Poland."

The communique also referred to an "atmosphere of fraternal friendship and comradely mutual understanding" in the Crimean talks -- a phrase apparently designed to minimize impressions of discord.

As usual, the document, distributed by the Soviet and Polish news agencies, gave little insight into the nature of the Crimean discussions. But it was clear that the Poles told their Soviet hosts that there can be no hope of normalization of the situation as long as Poland's economy continues on its downward slide.

The Poles were quoted as saying that the situation "continues to be complex and difficult," that industrial production is declining and that there are shortages of consumer goods.

In view of these difficulties, the communique said, "it has been decided at present to defer the payment of Poland's debt to the Soviet Union until the next five-year period and to supply raw materials for its light industry and also certain consumer goods."

Western diplomats here said Moscow had no option but to continue to supply the Poles with energy, raw materials and other commodities. Poland's declining productivity and production simply do not allow for repayments of debts at this stage. A Soviet refusal to provide additional assistance would produce a total economic breakdown and cause the sort of social unrest that could force Moscow to intervene militarily, a move the Soviets still seem determined to avoid.

The size of Poland's debt to the Soviet Union prior to the outbreak of industrial unrest a year ago is not known. Such statistics are regarded as state secrets in communist countries.

But Polish officials said that since last August, the Soviet Union is estimated to have supplied Poland with assistance close to $4 billion in the form of energy and other deliveries.

Western diplomats said that in the first quarter of this year Poland ran a $600 million balance-of-trade deficit with Moscow. The extent of Moscow's hard-currency support for Poland is also not known, but diplomats here say it ran about $500 million for the year.

The communique also appeared to have been designed to stiffen the resolve of an increasingly assertive Polish government to put an end to public disorders and demonstrations. Several new strikes are set for next week, including a protest against the continued detention of political prisoners. Solidarity has come out against this protest, as has the powerful Roman Catholic Church.

Yesterday, thousands of workers gathered for an open-air mass in Gdansk to celebrate Solidarity's founding there a year ago.

Archbishop Josef Glemp, Poland's Roman Catholic leader, said today in Czestochowa he feared more street protests and renewed his offer to mediate conflicts between workers and the government, The Associated Press reported.

"It is with some trepidation that we think of those marches that are supposed to be peace carriers," Glemp told about 300,000 pilgrims from the balcony of the Bright Mountain monastery, Poland's holiest shrine.

[It was Glemp's second appeal for calm in two days.Friday, he asked leaders of the government and Solidarity to "act prudently, stop instigating emotions and undertake tasks that have superior significance for the nation and state."]