Vienna — On Graben, the traffic-free pedestrian zone in the middle of this capital city, environmentalists are again busy collecting signatures for a year-old petition against the government's plan to build a hydroelectric power plant on one of the last unspoiled areas on the Danube.
Nearby, the exterior of St. Stephen's Cathedral is much cleaner now that automobiles - and their emissions - are kept out of the vicinity.
Five years ago, conservationists won a referendum that stopped Austria's first atomic power plant from going into operation on the Danube. Now a new government is planning to try again.
Meanwhile, an equally vigorous public campaign is being waged to secure a similar popular vote on whether a power plant should be built at Hainburg. Conservationists say that it would endanger the Auwald forest, a few miles down the Danube from here.
The Auwald is an ancient forest, home to storks and spoonbills, cormorants, heron, kingfishers, falcons, and plants and trees that are on international lists of threatened species. It is also a traditional recreation spot for the Viennese.
Austria's neighbors both East and West are also sounding new alarms now about the effect of modern technologies on their countryside.
Vast tracts of forest are dying, they say, because of the acid rain created by industry's emissions of sulfur dioxide and nitrogen oxides; cherished historic buildings are suffering erosion and waterways are being polluted to an extent that is dangerous to human as well as marine and animal life and agriculture.
Environmentalists here and in Hungary and Czechoslovakia are disturbed about proposals to build power plants on the Danube regardless of possible adverse ecological effects.
Ideology's absolute priority for industrial growth has in the past been a strong element in Eastern Europe's neglect of the environment.
Although the high costs of pollution controls have been a major consideration in governments on both sides, pressure for action is building.
Two major conferences this year each rated environmental damage in almost all countries as ''catastrophic'' and destined to become worse without radical and urgent action.
At a conference in Munich in June, 18 of 31 Western and East-bloc countries pledged to work for a 30 percent reduction of industrial sulfur dioxide emissions by the early 1990s.
More recently, a consortium of European nature and national park groups meeting in Britain called on governments and industry alike to mount a major campaign against the destruction already blighting the European landscape - from Britain's own Lake District to the threatened forests and waterways of middle and Eastern Europe.
At this stage, both the Germanys, Czechoslovakia, and Poland face environmental threats worse than Austria's.
On a stretch between Czechoslovakia and Hungary, only a little way downstream from Austria's Hainburg project, those two communist states envision a power plant near Bratislava, Czechoslovakia.
Czechoslovakia has the biggest energy problem of any country in Eastern Europe and a pollution problem comparable to East Germany's. But it has given scant rein to conservationist protest, either about acid rain's effect on the fabled Bohemian forest or the further industrialization of the Danube. It did not adopt the Munich ''30 percent'' prescription.
Nor did Hungary, presumably because it is so much less industrialized and thus does not have so big a problem.
Nonetheless, Hungary clearly is less than enthusiastic about the joint dam project, and public protest has made enough of an impact to prompt a government go-slow on a costly and at best dubious scheme to open the Danube to bigger vessels right across Europe - from Black to North Seas - quite apart from ecological and social hazards.
Many Western countries, including the United States and Britain - have stayed aloof from the Munich option.
But US and East as well as West European scientists are involved in an extensive antipollution program at an international ''think tank'' established at Laxenburg just outside Vienna a decade ago.
This is the International Institute of Applied Systems Analysis, which is in its second year of developing a computerized support project to help governments evaluate a variety of ''clean the clouds'' strategies.