Verbal fireworks are exploding over the world's longest undefended border.
At the center of this war of words between Canada and the United States is the environment - acid rain and pollution of the Niagara River.
Consider a recent speech in California by Allan Gotlieb, Canada's ambassador to the US. ''Acid rain has become a major issue in Canada-US relations,'' Mr. Gotlieb said. ''Acid rain has become a bilateral irritant.'' Ontario's minister of environment is more blunt. Keith Norton told visiting US journalists that President Reagan's apparent attempts to weaken air-pollution controls are ''close to an act of hostility on a friendly neighbor.''
Why is Canada so upset? It's because 50 percent of the pollutants which cause acid rain blow across the border from the United States. That means if Canada shut down all its smelters, closed its coal-fired generating stations, and parked all its cars, lakes would continue to die. In Ontario alone, acid rain threatens 48,000 lakes over the next 20 years.
According to Allan Gotlieb, the solution is to reduce emissions from old, dirty smelters and power plants. ''For their part,'' he says, ''Canadians are willing to bear this cost.'' Canada has offered to cut emissions in the eastern part of the country 50 percent by 1990, if the US will take similar action.
The two nations have signed a memorandum of intent to combat acid rain. So far, the result has been several telephone-book-size reports on the problem, but little else. According to David Hawkins of the Natural Resources Defense Council , the main reason for this is the Reagan administration.
''The administration campaigned on a promise of relaxing environmental regulations. That's what the business community wanted, and they are going to try and fulfill that promise,'' he says.