In Canada no less than the United States, smokers are a beleaguered minority these days. Under a Canadian law that take effect Jan. 1, most print advertising of tobacco products will be banned. A limited exception for billboard ads will remain in force only until 1991.

Furthermore, the law bars the promotion of tobacco products at sporting or cultural events except under contracts signed before Jan. 25, 1988. And it requires tobacco manufacturers to describe the health effects of the product on the package and to list the toxic chemicals in the tobacco and its smoke.In Massachusetts, meanwhile, public health officials are girding for a possible court challenge to a stringent anti-smoking law that became effective last Jan. 1. The law, first of its kind adopted by any state, prohibits newly hired firefighters and police officers from smoking on or off the job - even at home. Violators are subject to dismissal.

The first police appointments under the Massachusetts law are now being processed, and public service unions in Boston have indicated they may launch a legal challenge. But that will not be possible until there is a test case - an employee who is hired under the law and then fired for violating it.

A 1987 federal court decision suggested one avenue that an attack on the Massachusetts statute might take even though the plaintiff, a firefighter trainee in Oklahoma City, lost his case. He had filed suit after he was fired for violating a non-smoking pledge he had signed as a precondition of employment.

In its ruling, the 10th U.S. Circuit Court of Appeals in Denver considered whether there was "a rational connection between the (non-smoking) regulation and the promotion of the health and safety of the trainees."

The court held that such a connection did in fact exist, noting that "good health and physical conditioning are essential requirements for firefighters. They are frequently exposed to smoke inhalation, and it reasonably might be feared that smoking increases this health risk."

However, the court also observed that it was not "entirely rational" for the non-smoking regulation to apply to trainees only. It thus left open the possibility that the plaintiff might have prevailed if he had said his dismissal deprived him of "equal protection of the laws," as guaranteed by the Constitution.

A key aim of the Massachusetts law was to bring the rising cost of disability pension benefits under control. With firefighters particularly, regular tobacco use can aggravate heart- and lung-related illnesses caused by years of exposure to smoke from fires.

Similar concerns led USG Acoustical Products Co., a manufacturer of ceiling tiles and fiber insulation, to introduce a strict no-smoking policy in early 1987.