By JOHN TAGLIABUE, Special to The New York Times

Tadeusz Mazowiecki, who is expected to be nominated for the post of Prime Minister on Saturday, is a prominent Roman Catholic layman whose appointment underscores the influential role of the church in Poland's political affairs.

The nomination of Mr. Mazowiecki (his name is pronounced tah-DAY-oosh mah-zoh-VYET-skee), also confirmed the fruitful bridge between Poland's intellectuals and the millions of workers who are the backbone of Solidarity, a link that has been pivotal to the rise of the movement.

Many assumed that Lech Walesa, the Solidarity leader, would take the Prime Minister's job. But by accepting Mr. Mazowiecki, Mr. Walesa implicitly acknowledged that he may be more useful as a strategist in the opposition movement he leads than as an official thrust into the day-to-day running of the state administration.

Helped End 1988 Strikes

Over the years, Poles entrenched in church politics and the struggles of the embattled political opposition have come to know Mr. Mazowiecki, a 62-year-old journalist, as a tireless toiler for expanded rights, though few would have expected this sudden plunge into the eye of the political storm.

Mr. Mazowiecki's most important recent role was as the mediator appointed by the Polish Primate, Jozef Cardinal Glemp, to bring an end to the waves of labor unrest that shook the country last year. The process led to the so-called round-table talks on political change between the Communists and Solidarity and to the national elections in June that produced Solidarity's rise to greater power.