The powerful Catholic Church of Poland is facing a serious future leadership crisis - although it would be hard to discern this during Pope John Paul II's current triumphant journey through his native country.

The problem is one of fate and age. Cardinal Stefan Wyszynski, the Polish primate who has led the church here for 30 years and symbolizes - for Poland's 30 million Catholics - the kind of moral authority that the state lacks, is getting old.

Although still very active, he will be 78 in August and his friends say he is not in good health.

Until last fall there was little reason for Polish Catholics to be concerned. The man likely to succeed Wyszynski as primate was an equally able and fiery defender of the faith who had labored for 20 years in the primate's shadow, Cardinal Karol Wojtyla, archbishop of Krakow.

With the stunning election in October of Wojtyla as pope, however, one of Poland's two most powerful and respected cardinals is now in Rome while the other ages here.

Most importantly, says a leading Catholic intellectual, "there is no clear successor to Wyszynski now, no one of comparable stature. There is no one to whom transfer of such respect and popularity could be accomplished with confidence."

Although Wyszynski was a relatively unknown when he became archbishop of Gniezno and Warsaw in 1949, he has grown over the years into the most powerful unofficial leader in Poland. Poles have become used to church leadership that is not only strong and personal but skilled as well, one that is able to fight the church's battles against an officially atheistic government without provoking unrest that could get out of hand.

Thus, the question of succession here is not just a matter of increasing importance within the private confines of the church, but also among governemnt leaders here and elsewhere in the East and in the West.

Furthermore, according to some church sources, Wyszynski is increasingly driven by a sense that the country is endangered by a collection of problems ranging from continuing economic distress, to lack of major progress in church-state relations, and the continued Soviet presence.

If he is right, then his successor becomes even more important because Wyszynski has carried out one of the great balancing acts of the postwar era in Eastern Europe.

Although outspoken and sharply critical of Communist authorities on the key issues of church and human rights, the Polish primate is also widely viewed as a patriot who feels that the church, because of its moral authority, must also play a role in keeping the peace in Poland.

Nevertheless, he and Communist Party chief Edward Gierek are seen by many as believing each one is lucky to have the other: The cardinal to help keep the lid on and Gierek to extract whatever he can from Moscow in terms of maneuvering room for such a formidable church.

Many seem to feel that if Gierek were ousted, a more hard-line leader would be imposed. Everybody, including dissidents, seems to want to avoid this for fear things might get out of hand and provoke Soviet intervention.

Several names are heard in church circles about a possible successor, including: Archbishops Henryk Gulbinowicz of Wroclaw, Jerzy Stroba of Posnan, Franciszek Macharski of Krakow, and Bishops Bronislaw Dabrowski of Warsaw, Wladyslaw Rubin of Rome, and Ignacy Tokarczuk of Przemysl.

Although the state, which must give its approval, will be a factor in the selection, a bigger factor may be the pope, with his special ties to Poland and his understanding of the requirements for church survival in the communist East.

Most of the names being heard were of persons appointed by Wyszynski and some sources here suggest that the pope might look to someone else.

Because of his close ties to the pope, considerable attention is focused on the 51-year-old Macharski, whom the pope just appointed as a cardinal.

Others, however, say the new cardinal is so identified with the pope that they wonder if he would have a personality of his own. There is also considerable interest, especially in Rome, in Wladyslaw Rubin, whom the pope also just named as a cardinal.

In general, the names being heard fit into groups. Some feel the church-state working relationships developed while arranging the pope's visit will endure, and that figures such as Dabrowski, secretary of the Polish episcopate and one who dealt extensively with the government on the visit, will emerge as a leading candidate of a group that favors cooperation.

Others with a distrust of the ruling Communist Party but perhaps following Wyszynski's pattern of more limited cooperation form a second group. Gulbinowicz, sources here suggest, is becoming a favorite of Catholic intellectuals, while Stroba is said to be looked upon with caution by dissident intellectuals and Tokarczuk as too outspoken on human rights to get past the government hurdle.

"Whoever is chosen," one church specialist here says, "will have a completely new situation after 30 years of Cardinal Wyszynski." CAPTION: Picture, CARDINAL WYSZYNSKI