As at so many crucial moments in the past, Poland's powerful Roman Catholic Church has again come to the aid of a weakened communist government.

During more than three decades as primate of Poland, Cardinal Stefan Wyszynski has become renowned for his unbending defense of church interests in its daily battles with the state. But at times of national crisis, he has proven himself to be the authorities' most reliable ally.

Now, in advance of emotional ceremonies marking the 10th anniversary of the bloody suppression of workers' riots on the Baltic coast, Wyszynski has appealed for restraint and social peace. Thanks partly to his considerable influence with the leaders of the new independent labor union federation, Solidarity, the theme of national reconcilation -- rather than bitter recrimination -- is likely to dominate remembrance services beginning Tuesday.

With the Kremlin watching intently, the authorities are desperately concerned that expected mass demonstrations in the Baltic ports of Gdansk, Gdynia and Szczecin on Tuesday and Wednesday should pass peacefully. According to official figures, about 50 Poles were killed in clashes between workers and militia in December 1970.

Today, prayers were said in churches throughout Poland for unity to ensure that "the institutions of our state remain secure and the sovereignty of our nation is not endangered." Last week, Poland's bishops warned of dangers to the country's independence and even criticized several dissident groups for "provocative statements" directed against the Soviet Union.

The somber tones of the warnings, combined with private briefings by senior church officials, indicate that Wyszynski is seriously worried by the possibility of a Soviet intervention. One of his close aides remarked: "The cardinal's overriding preoccupation is the perservation of Poland's national identity. This concern has guided his actions and statements through the present crisis."

The special position occupied by the Catholic Church in Poland is due in large part to the 79-year-old Wyszynski. Unlike church leaders in some other East European countries, he refused to submit to government pressure and persecution, particularly during the period of Stalinist rule in the late 1940s and early 1950s.

Similar defiance might have led to death or prison in other Soviet Bloc countries but for Wyszynski, it resulted in banishment to a monastery in 1953. It earned him the support of Poland's overwhelmingly Catholic population and the grudging respect of Communist officials. The restrictions were lifted in 1956, during Poland's peaceful "October Revolution," and he returned in triumph to the primate's residence in Warsaw.

Through his appeals for calm and reconciliation, Wyszynski helped Poland's leader of the time, the nationalistically inclined Wladyslaw Gomulka, to consolidate his rule. Thanks to their joint efforts, the revolution was controlled and there was no Soviet invasion -- in contrast to Hungary where the Red Army was sent in to crush a popular uprising.

The primate played a similar role when Gomulka, who had become increasingly authoritarian, was ousted in 1970. Describing the strikes then as "unprecedented in our history," he told the workers: "We beg of you, do not accuse. Show understanding, feel compassion, put your hands to the plough."

Wyszynski's height, powerful build, and strong facial features give him a charismatic presence. In his red cardinal's hat, he looks every inch a prince of the church -- but also a member of the old Polish nobility.

A father-like figure for many Poles, Wyszynski is deeply conservative in his pastoral teaching. He has described abortion and birth control as "genocide" and treated the reforms of the Vatican II Ecumenical Council with considerable suspicion. But, under his leadership, the Polish church has become the chief repository of the nation's identity and a symbol of resistance to Communist rule.

It is no accident that many of Solidarity's leaders, including Lech Walesa, are deeply religious and look to the church for guidance. Walesa has described Wyszynski as "my number one adviser" and insisted that, as long as he is Solidarity's leader, a crucifix will hang on the wall of the union's committee room.

Close friends of Wyszynski say he realizes he must act not simply as a religious leader, but also as a politician. A prominent historian remarked that the head of the Polish church has always had a political as well as pastoral role. In the 18th century for example, the primate acted as regent between the death of one king and the selection of another.

"The same thing is happening today with our Communist leaders. Every time a leader is deposed, authority seems to return to the primate. We're in a kind of interregnum right now," the historian said.

Wyszynski's moderating influence is also appreciated by the Communist authorities who are quick to appeal to him when in trouble.

One government official commented: "With Wojtyla [Pope John Paul, who was a cardinal here], we always felt he owed his first allegiance to Rome. But with Wyszynski we know where we stand. He is a Pole first and a Catholic only second."

Last August, when the then Communist Party chief, Edward Gierek, apparently persuaded him there was a risk of imminent Soviet action against Poland unless strikes were called off, Wyszynski delivered a televised sermon urging that strikes be used only as a last resort.

He intervened again during the dispute over Solidarity's registration last month. Flying back from Rome after a meeting with the pope, he was told that the government was ready to declare a state of emergency unless the union formally recognized the leading role of the Communist Party. Once again, he appealed for moderation.