CONCERTED international efforts are under way to stop the air pollution that causes acid rain. Nations that are attacking this problem are strongly pressuring two other countries to join in: the United States and Great Britain, both of which are adjudged a major part of the problem.
Canada and nine European nations recently agreed in Ottawa to reduce sulfur emissions by at least 30 percent over the next 10 years. Four of the 10 - Canada , West Germany, France, and Norway - are aiming for a 50 percent decrease.
Acid rain, which stems from sulfurous air pollution, is blamed increasingly for damaging forests, lakes, and even monuments. Winds spread pollution generated by one country across several other nations, where it comes to earth in the form of overly acidic rain. Charles Caccia, Canada's minister of environment, says that ''over half the acid rain falling in my country has its origins'' in the US. ''And, conversely, a significant proportion of the acid rain which falls (in the US) comes from Canada.''
This June in Munich, West Germany will play host to an international conference that will concentrate on the issue now emerging as Europe's primary environmental concern: forest damage. Germany is concerned about the considerable harm occurring to trees in its renowned Black Forest, among other areas; this damage is often attributed to acid rain. One reason Switzerland is concerned about acid rain is that maintaining healthy hillside trees is important in diminishing the prospects of avalanches.
In September there will be another international conference on acid rain, this time in Geneva. This one is expected to deal with the whole spectrum of the problem.
The 10 nations that have agreed to at least a 30 percent sulfurous reduction have figured out, at least in broad outlines, how to achieve their goal, environmental sources say.
Thus the 10 nations that signed the Ottawa accord are intent on pressuring the US and Britain into taking similar action to reduce sulfur emissions.
For months Canada has exerted direct governmental pressure on the US government without apparent success: It had been seeking direct action to reduce the pollution, but the Reagan administration decided instead to increase research on the problem.
Similarly some internal pressure already exists on the London government of Prime Minister Margaret Thatcher to decrease Britain's sulfurous pollution.
Surely, the eventual solution must be international - because the problem is shared.