Vienna — From Eastern Europe to distant China, Communist parties are facing challenges from new thinking within their own ranks. Recent offical statements suggest that parties fear a slipping hold on the ''hearts and minds'' of the people they rule.
Lately, there has been growing opposition within various Communist parties to efforts to preserve a Soviet-style ''monolithism'' and to Moscow's lingering insistence on the relevance of a Soviet model for all parties.
This, in turn, has prompted strong conservative opposition to change - above all to anything that questions the party power monopoly and the system itself.
Because of its economic and political crisis, this conflict of ideas is most visible in Poland. But Hungary, too, has been discussing options for reform more or less openly.
Closed regimes like those in Czechoslovakia and Romania continue ostrich-like claims to an ostensible party unity. But the hard line against any thinking that diverges from the party line suggests ''unity'' remains elusive.
Outside the East bloc, even the Yugoslavs are taking a searching look into weaknesses in their system, despite their break with Soviet concepts 35 years ago.
Debate over how a party could operate best today is being intensified for two reasons. One is the worsening economic crisis they all face. The other is the widening gap between the generations within the party itself, and the rift between the party and the public outside of it, which is often broadly socialist-inclined.
In Yugoslavia's case, there is disagreement over the direction that an established society must now take.
At a recent seminar of Yugoslav party and nonparty sociologists, the most strongly supported views came from the ''liberal'' Praxis group of Marxist professors excluded from the University of Belgrade in the 1970s for advocating major party reform. Equally striking was the wide reporting their views received in the Yugoslav news media.
The one-time Serb communist leader, Mijalko Todorovic, has openly charged that Yugoslavia's system of self-management is being nullified by the lack of more democratization of political life.
At an East-West symposium attended by Soviet and Western Marxists, the Yugoslavs' principal theoretician, Alexander Grlickov, said forthrightly that socialism could prove itself ''only to the extent it continuously expands . . . the horizons of democracy and freedom.''
He told the Russians that Marxism had lost ground because, instead of being treated as a science needing adjustment to the contemporary world, it had been turned into immutable ideology. That is as revisionist today as when Belgrade first told the same thing to Stalin.
In today's conflict over the future of socialism, there are two camps. On one side are the ''inevitabilists,'' still clinging to old shibboleths of certain ''ultimate victory'' over capitalism. The other side is manned with communists realistic and sophisticated enough to see that circumstances, and not outmoded theory, decide the course of events.
Poland is poised uneasily between dogma and reform. The latter is obstructed by a powerful conservative faction that, as a Warsaw commentator wrote recently, regards ''any threat to its own position and obsolete methods as a threat to the system.''
For the reform-minded Polish communists behind Gen. Wojciech Jaruzelski, the party's only chance of revival lies in winning over the country's two majorities - youth and the Roman Catholic Church.
The problem of youth is plaguing all the ruling parties, especially in East Germany and China.
East German youth are daily barraged with Western ideas via West German radio and television. As Politburo member Kurt Hager defined the problem, exposure to serious Western discussion of the problems of all modern societies makes East German youth increasingly skeptical about their own closed society.
On the other side of the Soviet world, China was seen last year as cautiously moving from the classic approach to communist rule, away from Stalinism toward interest in Western contact.
Since then, however, the party has apparently begun to perceive too much response to Western ideas. It has launched a ''socialist civilization'' campaign to halt a drift from socialism.
The problem, the People's Daily (almost echoing Mr. Hager) said, is that ''some people, especially young people, are wondering whether or not we still need the party's leadership, whether socialism is a superior system or not.''
Over everything, of course, hangs the Soviet question mark, especially in the absentee leadership by Yuri Andropov.
The Russian Party, Italian and Yugoslav communists say, is still Stalinist, ignoring modern reality and still presenting Soviet communism as conflict-free in Stalin's monolithic sense.
Most of the East Europeans have at least begun to sense the fallacy, though only Hungary has openly admitted it.
The Yugoslavs are debating more concessions to pluralism, at least in popular control of the party and stronger ''teeth'' for groups like trade unions.
Soviet thinking balks at anything like that, though Mr. Andropov, in his more visible days, approved of Hungarian reform. He even suggested some of it was possibly applicable to the Soviet Union's problems. Even should that not come about, Eastern Europe's ''modern'' communists are hoping that at least this modest green light will remain to help them meet the challenge from the hard-liners.