U.S. Army-sponsored researchers misled Canadians about the purpose of large-scale chemical warfare tests conducted in 1953 in Winnipeg, Manitoba, according to a Canadian defense spokesman.

The experiments, also carried out in St. Louis and Minneapolis, are becoming a subject of heated debate in Canada since they were revealed earlier this month in documents obtained in Washington under the U.S. Freedom of Information Act.

Acting on behalf of the U.S. researchers, Canadian defense authorities told residents of Winnipeg, then a city of 235,000, that the tests were to determine whether the city could be covered in a smoke screen to hide vital installations in case of attack.

But, according to the documents, researchers both in the United States and Winnipeg sprayed zinc cadmium sulfide in aerosol clouds throughout the city to simulate the fallout patterns that might be expected from chemical and biological warfare agents and nuclear radiation in the event of an enemy attack.

The Canadian government has begun an investigation to determine if spraying of the chemical was harmful or posed any danger to inhabitants. Zinc cadmium was used because it sticks to everything it lands on and is easily traced, a Defense Department spokesman said.

The spokesman said the project was not described fully because it was classified as secreta. "The cold war was getting into full swing at that time and it could have created anxiety among the population," he said. A University of Manitoba pharmacologist said after the tests were revealed here that both cadmium and zinc are toxic and could be dangerous to babies, old people, asthma sufferers and the sick.

According to the Defense Department, 14 tests were conducted in Winnipeg between July and September 1953 by the Parsons Corp., of Los Angeles under a U.S. Army contract to Stanford University. The Canadian Press news agency carried the story of a Toronto man who said he was involved in the experiment. That man claimed the tests may be linked to respiratory problems he has suffered since 1959.

The tests were revealed in documents obtained by American Citizens for Honesty in Government, a group associated with the Church of Scientology.