Vienna — Yugoslavia is going through a worrisome period, not only economically but also politically. This seems to be the meaning of Milovan Djilas's first direct brush with the authorities in some years, rather than a signal of some drastic crackdown on Yugoslav dissidents.
Mr. Djilas - once a close associate of President Tito and later one of his harshest critics - made relative light of his detainment by police late Friday. He spoke with this writer by telephone Sunday from his Belgrade home.
Mr. Djilas was taken into police custody along with some 30 well-known Belgrade intellectuals who had gathered in an apartment to hear him talk about Yugoslavia's nationality problems.
Djilas was ''not formally arrested,'' he told the Monitor. His interrogation lasted not 18 hours, as earlier reported from Belgrade. ''The actual questioning of myself lasted only about 15 minutes,'' he said.
Such informal groups have proliferated - for the most part unmolested - in Belgrade, Zagreb, and the other Yugoslav provincial capitals in the post-Tito period. They focus on widely differing ideas about Yugoslavia's problems and its future development.
Within the ruling League of Communists itself, there is continuous argument between those (in the present leadership) who support cautious liberalization, and those who want a major return to centralization and firm party control.
The topic on which Djilas was invited to talk to this particular group - the nationalities - has been an especially sensitive one since the open revolt in the Albanian minority Kosovo region of Yugoslavia a few years ago. This event itself triggered a wave of Serbian nationalism, which, in turn, struck echoes amid nationalities in other republics.
Djilas, however, sees no particular connection between his Friday evening subject and the police action.
It was, in fact, his first meeting with the group, though it had been functioning informally for three years. It may, therefore, have been his own presence which triggered the police raid and prompted the first official explanation that the group was taken in for ''verification'' on suspicion it had met to promote oppositionist political activity.
''I did not speak of my general political ideas,'' Djilas said, ''only of the nationalities problem with which we (the party) had to deal from the onset during the war.''
He sees the authorities' move, therefore, as more than anything else ''some continuation'' of the prolonged endeavor to isolate him - but in ''in softer terms.''
''I am convinced,'' he added, ''that it will not become a court matter.''
Djilas is not unused to such treatment. In the late 1950s and through the '60 s, Djilas's articles and books published in the West brought him into frequent, bitter, head-on conflict with the regime. He has served a total of nine years in prison, his final release coming in late 1967.
He has continued writing, and though he became increasingly remote from Yugoslavia's political scene, he was still occasionally subjected to sharp campaigns in the official news media and by some of his former top associates.
Before last week's incident, he had come under attack both shortly before and following President Tito's passing in 1980, when Belgrade (particularly after Tito) wanted to ease strains on its relations with the USSR.
Yugoslavia now is roiled by its ethnic conflicts, a tussle between the party's left and right, and an economic crisis. Uncertainty about economic recovery will continue until recent support from the International Monetary Fund and the West begins to take effect - if the aid is granted.
With this background, the latest Djilas questioning may be little more than a warning to all the differing groups and opinions which flourish virtually openly.
The ''liberal'' features which distinguish Yugoslavia from all other communist states remain, including the candid official acknowledgement of failures, errors, and social grievances, and the open debate about them.
Above all, the Yugoslav press continues to insist, despite intermittent sanctions, to be a forum for the necessary ''clash of ideas.''