Poland's communist leaders today joined the country's overwhelmingly Roman Catholic population in disbelief and anguish at the assassination attempt on Pope John Paul II, whose Polish heritage has given him added importance to a people who already have strong links to the Vatican.

State radio and television broke into their programs to carry live reports from Rome about the pope's condition and details of the shooting. Groups of stunned Poles, some of them weeping, gathered around television sets in public places and stopped each other on the street.

The assassination attempt came as a particular blow because it coincided with news of a serious deterioration in the health of the Roman Catholic primate of Poland, Cardinal Stefan Wyszynski. News of the attack on the pope was initially withheld from the 79-year-old cardinal in view of his grave state.

The death of either leader would have considerable political implications here in view of the involvement of the Roman Catholic Church in the reform movement in Poland. Wyszynski, in particular, has frequently acted as a trusted intermediary at times of crisis between the independent Solidarity trade union and the communist authorities.

Congregations throughout Poland have been asked to pray for both the pope and the cardinal, who had led the church here since 1948. Before assuming the papacy in 1978, Karol Wojtyla was archbishop of Krakow and, in effect, Wysznyski's deputy.

The feelings of many Poles about the assassination attempt were summed up by one of the pope's oldest friends, Jerzy Turowicz, editor of the independent Catholic weekly Tygodnik Powszechny. He said: "A man who preached love has become a victim of hatred."

An independent member of parliament, Jan Szczepanski, said: "For us Poles the assassination attempt is particularly hard since during these difficult times he has been a moral, social and political mainstay."

Poland's three top political figures, Communist Party chief Stanislaw Kania, Prime Minister Wojciech Jaruzelski and head of state Henryk Jablonski, said the news of the attempt on the pope's life came as "a great shock to the Polish nation and the state authorities." In a telegram, they wished him a speedy recovery from his "homeland" and "strength to fulfill your mission in the service of the humanistic ideals of peace and the welfare of mankind."

In a message read over Polish television, the nation's communist leaders said, "Your Holiness: the news of the criminal attack on your life has deeply moved our nation."

In the absence of Solidarity leader Lech Walesa, who is visiting in Tokyo, the union's vice-chairman, Bogdan Lis, sent a message to the pontiff describing his suffering as "a symbol of love for man" and said "we are shocked by the news."

The Polish episcopate said the whole nation was praying for the pope's quick return to health and active service.

News of the assassination attempt spread rapidly in Warsaw and other Polish cities and quickly became the main subject of conversation but, in public at least, most people kept their emotions to themselves.

Motorists in Krakow, where sympathy for John Paul II is perhaps most intense, were seen weeping as they listened to their car radios.

"What times! To shoot the pope, the pope from Poland!" a woman in the city of Poznan, west of Krakow, was quoted as saying. "This is the most tragic period in our history."

"All is against us Poles," cried an engineer in Warsaw. "What have we done that God is punishing us so severely?"

Although less involved that Wyszynski in Poland's day-to-day drama, the pope has kept in close touch with events here. He has become both a symbol and source of inspiration for the independent trade unionists, including Walesa who made a pilgrimage to the Vatican in January.

Many Poles believe that the pope's election helped touch off the present drive for reforms by giving the nation a new sense of confidence.

News of the sharp deterioration in Wysznynski's condition was carried by the Polish news agency PAP quoting church officials. It was the most pessimistic bulletin yet issued on the primate who has been ill in bed for the last six weeks.

There have been conflicting reports on his state of health with a church spokesman flatly denying suggestions that he has cancer. At first his illness was described as a "gastronomic disorder," but privately aides now concede that chances of a full recovery are very slim.