Brussels — The European peace movement, stunned by its recent success, is tuning up for an encore. In the past two months an estimated 2 million demonstrators have taken to the streets - from Bonn to Rome to Amsterdam - in the greatest outpouring of antiwar sentiment in Western Europe since the 1960s. Now, taking a breather, the movement has begun to plot its next move.
''Relax, enjoy the holidays,'' E. P. Thompson, the spiritual father of the movement, told an eight-nation strategy meeting in Brussels Dec. 6. ''You've earned the right. Next year will be even more demanding.''
The feeling among European antiwar activists is that until now events, more than leadership, have shaped the movement, and that that must change.
''People have poured onto the streets in response to the saber rattling of the Reagan administration,'' Mr. Thompson said. ''If the European peace movement has been orchestrated,'' he said, alluding to charges that Europe's peace activists have been funded and directed by the Soviet Union, ''it has been by Reagan, Weinberger, and Haig. We must begin to orchestrate ourselves. We must find our own conductor.''
No doubt, in 1982 the European peace movement will continue to ''orchestrate'' the same sorts of activities that captured the world's attention this fall - mass rallies in major cities. Scores of demonstrations are already planned for next spring.
But beyond that, according to the movement's leaders, two new directions, at least, will be pursued in the coming months.
One is to broaden the scope of the appeal to include the communist countries to the east and the United States to the west. Representatives of several European peace organizations will visit the US on a 40-city tour next spring.
''Perhaps most importantly, we must dig tunnels to the East,'' Mr. Thompson said. ''We must build links with professionals, students, peace groups, and dissident movements in Eastern Europe, including the Soviet Union.''
The day before Thompson spoke in Brussels, some 100,000 demonstrators had turned out in Palace Square in Bucharest, Romania, in support of the government's antinuclear campaign.
The other direction the European peace movement is expected to take next year is toward building a nonaligned political base to act as a ''steering power'' for the disarmament talks between the US and the Soviet Union in Geneva.
''The new European peace movement,'' said Miet Jan Faber, leader of the Dutch Inter-Church Peace Council, a guiding light for antiwar organizations elsewhere in Western Europe, ''must be made to give political shape to the social processes that so far have motivated the movement overwhelmingly.''
Mr. Faber said that creating ''European political counterweight'' to the Geneva talks could involve:
1. Tightening the links between various national peace movements.
2. Drawing in other social groups such as trade unions, the academic community, and professional organizations.
3. Reaching out to the government level.
''The new peace movement,'' Mr. Faber said, ''must, on the one hand, act as a steering power for the Geneva talks, pressing the superpowers to accept our goal of a nuclear-free Europe, and, in the broader sense, it must act as a stabilizing force allowing the US and the Soviet Union to melt the cold-war ice that separates them today.''
Analysts say, of course, that the direction the European peace movement takes depends as much on the course of events - especially the arms negotiations in Geneva - as on plans made by the movement's leaders.
But it is clear that the remarkable, even unexpected, successes of this fall have given the European peace movement confidence, a feeling that its aims can be realized.