A revival of religion in Czechoslavakia, part of an East-bloc-wide phenomenon , is being fostered by two very disparate sources:
* One is the ''talking samizdats,'' tapes made from religious programs broadcast by Western radio stations. (''Samizdat'' is a Russian word for underground ''self-publication.'')
* The other is a new group of Czech composers.
For thousands of young adults in Prague, Sundays begin with Radio Austria's broadcast of a Roman Catholic mass. An ecumenical discussion follows, and concludes with an organ mass at 11 a.m. in one of Prague's many beautiful baroque churches.
Petr Eben is the leader of the revival. The half-Jewish survivor of Nazi terror is internationally known through his work in West Berlin, Salzburg, the United States, and Great Britain. He reportedly started the revival by playing his own compositions in Saint Jacob's Church, located deep in the heart of Prague's old city. The church is a flamboyant, majestic edifice in pink and white marble, and it is packed on Sunday mornings.
The audience listening to the mighty organ includes many East German tourists , nearly all young. Like their Czech and Hungarian counterparts, they can receive high-quality FM broadcasts without special equipment. Their ''front-line'' position allows them to perform a rewarding service: they make the cassettes for East-bloc residents living farther east.
Cassettes are also used to spread Western pop music. The tapes can be heard in many East-bloc restaurants. Be they on Bach, Elton John, or religion, cassettes are one commodity in the vast, informal barter system comprising such goods as auto parts, Western clothes, and fresh fruit.
The Czech government's reaction to the religious enthusiasm has been to isolate the intellectuals leading it. ''The authorities are deathly afraid of another Poland,'' says a prominently placed Czech music authority.
Four leading theater directors were recently ''turned off'' (denied any further work) for having designed a stage set featuring two sets of stairs meeting at a right angle. The set looked like a cross.
The recently-completed Palace of Culture in Prague, a modern convention hall with exquisitely bad acoustics, now features competing ''organ matinees'' on Sundays.
A young Slovakian puppet player explains the differences between written and spoken samizdats. ''Talking samizdats are more communal than written ones. Written ones you read alone. A cassette can be the basis for an evening, and they don't have to be religious.''