Vienna — Yugoslavia's Muslims, the country's third-largest religious group, are becoming restive. To a government without one strong leader at the helm, drifting backward economically and awash in foreign debt, this religious upsurge is an unwelcome development.
In August, 11 Yugoslav ''Muslim nationalists'' were sentenced to 90 years' imprisonment between them for spreading ''pan-Islamism'' and wanting to turn Bosnia-Her-zegovina into a separatist Muslim republic.
The trial produced the heaviest and biggest crop of political sentences handed down in Yugoslavia since the Stalinist years after the war.
The harsh judgment has set observers to pondering whether Yugoslav authorities fear that mounting Muslim unrest in Yugoslavia could be more disruptive than the nationalism that spawned Albanian riots in the southern province of Kosovo two years ago.
The Yugoslav leaders have on their hands acutely worrisome and growing nationalistic echoes of old ''separatist'' talk in several parts of the country.
More serious still, there is no one national leader like the prestigious Josip Broz Tito - who was often ruthless in dealing with ethnic separatism - to cope with them. Since Tito's passing in 1980, the country has been run by a multinational collective leadership representative equally of the six republics and two regions (Kosovo and Vojvodina).
The 1981 riots in Kosovo laid a fuse that snaked a way outside its own borders to ignite new waves of nationalism, also of a politically religious hue, in several republics, especially in Bosnia-Herzegovina.
Bosnia-Herzegovina is home to almost half of Yugoslavia's 4 million Muslims. Two million are Slavic, the bulk of them in Bosnia-Herzegovina; the rest are spread through the other republics. Two million non-Slavic Muslims live largely in Kosovo and Macedonia.
Almost all are Sunnis, which means the militants among them - including a young Muslim movement with a tradition and terrorist past going back to the prewar Yugoslav kingdom - are not necessarily supporters of a Khomeini-style Islamic revolution.
But many are fundamentalists and fanatic in demanding a ''purely Muslim'' Bosnian republic.
Only a few years ago, one could observe that attendance at the mosques, even in Kosovo or Sarajevo, the capital of Bosnia-Herzegovina, was meager.
But the once-aging and shrinking religious community has been rejuvenated by a young generation, which has imbued it with the new political meaning for Islam touched off by the Iranian revolution of 1979.
Nationalism has always had a snowball effect in Yugoslavia - from Croatia to Serbia in the early 1970s, from Kosovo in 1981 to the even bigger Muslim community in Bosnia-Herzegovina a year or so later. But it may not benefit any nationality - Serb or Croat, Orthodox or Muslim - to push things to any kind of separatist breakup of a union that many analysts say has benefited them all.