Poland's martial-law government yesterday denounced President Reagan's imposition of economic sanctions as an "unprecedented" interference in internal Polish affairs, while Premier Wojciech Jaruzelski denied reports of dozens of deaths during 12 days of military rule.

In a 10-minute speech to the nation broadcast over Radio Warsaw and monitored in London by BBC, Jaruzelski said, "The reports of alleged tens or hundreds of fatal casualties, of thousands arrested, held in the frost, beaten up and tortured, are a lie. One cannot hide the truth about Poland in Poland. Sooner or later, it will be known to the world."

The Polish primate, Archbishop Jozef Glemp, issued his own Christmas message, to be read at midnight masses throughout the country, in which he painted a bleak picture of life in Poland during 1982--a year of "self-denial, want, sacrifice and humiliation."

"What can I say to those wronged, to the disappointed and humiliated, those unjustly detained and slandered?" the message read. "What real sign of hope can we give them? There is only one. We are still alive, and life is a gift of God." News agencies reporting on the message from Rome said it had been delivered to Pope John Paul II there earlier this week by Polish Bishop Bronislaw Dabrowski, secretary of the Polish bishops' conference.

The government-run media also announced that the underground occupation by more than 1,100 workers at the Ziemowit mine had been broken, with 350 miners coming to the surface by early morning and others giving up their strike throughout the day. Radio Warsaw said 900 miners, out of more than 1,700 on strike at the Piast mine, also in Silesia, remained underground, protesting martial law. No violence was reported at the mines.

Apparently in reference to U.S. economic sanctions against Poland announced Wednesday by President Reagan, Jaruzelski said "one gets the impression that someone is keen on Poland being a country in chaos, an insolvent debtor, the sick organism of the continent." It was the Communist Party leader's first national address since martial law was declared Dec. 13.

A statement released earlier in the day through the government news agency PAP said Reagan had "interfered in Polish internal affairs in an unprecedented manner," which would affect "the living standards of Polish families."

That statement was similar to, but far less strident than, a series of Soviet denunciations issued yesterday accusing the United States of instituting an "economic blockade" of Poland with new prohibitions on food shipments, government loan guarantees and technology transfers.

Overall, Gen. Jaruzelski's speech was moderate in tone, similar to his initial martial-law proclamation nearly two weeks ago. While warning that the current situation demanded "observance of the severe orders," he said, "I declare that this state of martial law will not be in force one hour longer than necessary.

"I realize how the rigors of martial law have complicated everyday life and thwarted personal plans," Jaruzelski said. "In the history of Poland, moments have occurred more than once when it was necessary to choose not between good and evil but between a greater and lesser evil. We carried out this choice. I believe the future will judge this choice justly."

Jaruzelski said the government had not given up hope that "emergency measures would not be necessary" until the last minute. "I believed that a way to a compromise way out of the dangerous crisis would be found. But for there to be accord, there has to be good will among all partners. This good will was lacking. We now know today who did not display this, who proclaimed confrontation," he said in a clear reference to what the government says were militants within the Solidarity trade union movement seeking to overthrow the Communist system and sever military ties with the Soviet Union.

For the future, he said, "nobody intends to nullify the fundamental principles of renewal," the word Poles used during the rise of Solidarity to define political, social and economic changes.

Promising that "there is room for self-managing and really independent trade unions...there is room for worker self-management," Jaruzelski said martial-law authorities "do not want vengeance or a lowly squaring of accounts. There will be no military dictatorship in socialist Poland, but also there will be no room for dismantling the state or for the supporters of confrontations."

"In the near future," he said, the government "will present a program of our intentions to the community." In one of several references to popular reaction to the military government, he said, "It is difficult today to ask for the credit of confidence. Let deeds and not words support us."

"The introduction of martial law," Jaruzelski acknowledged, "represented a profound shock for the whole of society, for all citizens. We did not want as much as a single drop of blood to be shed. We counted on that. Unfortunately, we did not succeeed in avoiding that."

He repeated the government's contention that, despite independent reports from inside Poland that dozens of striking workers have been killed in confrontations with security forces, the sum of the deaths under martial law has not exceeded seven miners killed last week at the Wujnek mine in Silesia.

"We all grieve over the events that took place" there, Jaruzelski said. "That is also my personal drama." But responsibility for the deaths, he said, is with the "ringleaders" of the strike who "broke the law of the state of war."

In other news broadcast by the Polish media and monitored in London by the BBC, the government announced that Jaruzelski had met with Archbishop Luigi Poggi, an emissary from the pope who was allowed to enter Poland last weekend. The subjects of their talk, Warsaw domestic television reported, were "the situation in Poland, Polish-Vatican relations and the shaping of relations between the state and the church in our country."

Warsaw domestic radio service reported that Katowice Province, where a steelworkers' strike was broken this week, was returning to normal, "despite the still existing flash points." The report said that "supplies of rationed foodstuffs have improved in the past few days" as shipments of goods arrived, including "the first deliveries of rice from the Soviet Union."

A report in Zolnierz Wolnosci, the Army newspaper, reviewed on Radio Warsaw, said the "struggle against counterrevolution" was now "entering the decisive stage. Survivors from Solidarity's extreme faction, as well as elements from subversive groups which missed being interned are again making their ranks cohesive. Signs multiply pointing to the fact that reaction is going underground."

PAP news agency also transmitted a commentary by the government press office saying that, despite "rumors that a purge is in progress in the administration, opinions of this kind are wrong." The report said that in the first week of martial law, four regional governors, three deputy governors, 77 mayors "and also top executive officers of the towns and parishes were dismissed. Personnel changes have been carried out in 29 of the 49 provinces." The report said at least 20 percent of the changes had been due to regular retirement.

Zolnierz Wolnosci printed one of what has been a series of question-and-answer sessions with Polish Communist Party Central Committee Secretary Marian Orzechowski, entitled "the Party and the Martial Law--New Problems, New Questions."

The sessions appear to be designed to transmit instructions to party members and activists throughout the nation, to allay fears that the party position has been subordinated to the military while at the same time warning members that all are being tested in what Orzechowski called "a time of purge."

Orzechowski made repeated references to the "enormous opportunity of the times we are witnessing," always coupled with the warning that "we must not waste this opportunity."

"I do not close my eyes to all the divisions that continue to exist within the party," he said. "This would be dangerous shortsightedness. But it seems to me that...unity is the most important issue now and that under the conditions of the martial law the only yardsticks by which to evaluate a party member are his activity and his attitude toward the main issues of the present day, including the issue of martial law. This is also a question of attitude toward Solidarity, toward how the party is to behave and act and toward responding to the instructions issued at party levels."

Still, Orzechowski said, there are "spontaneous grass-roots initiatives" within the party, and a "feeling of belonging....These are still not massive features, although I am convinced that this trend will become increasingly stronger."

But in an indication of more purges to come, he said, "Only some sections of our party members--unfortunately a minority--are passing the present trial."

On the question of "whether it was right to introduce martial law," Orzechowski said, "Such discussions have been completed and settled."

The authorities' dialogue with the people, Orzechowski said, will grow stronger "because more and more people realize that the martial law is our last chance. There is nothing beyond it. If we lose this chance we lose everything. However, I am convinced we will not lose."