SOMETIMES SCIENTIFIC opinion on health and safety issues reverses itself, so that a product once considered dangerous for human consumption will turn out to have been relatively risk-free... and vice versa. But the growing mountain of evidence that smoking cigarettes is bad for you seems to be unbudgeable -- and it is getting more so every year as additional evidence is piled on. That is the nub of the matter, and it's what you need to remember as the ashtrays start flying in this year's annual exchange of abuse between the friends and foes of cigarette smoking.

The occasion for the melee was the release the other day of a mammoth new surgeon general's report on smoking and health, which came 15 years after the first report of the surgeon general on this subject, and many thousands of reserch papers later. For smokers and for the tobacco industry, the news was bad: The evidence grows ever less tentative and ever more demonstrable that cigarette smoking does serious and, all too often, mortal damago to the human body. In effect, this new report, which compiled the work that has been done since the 1964 report was made, was, predictably, subjected to some kind of preemptive attack by the stalwarts at the Tobacco Institute. They disparaged it as a rehash and and dwelt on what they called an idiosyncratic excess of zeal on the part of anti-smoker, HEW Secretary Joseph Califano.

Tobacco partisans had already revealed their absolute unwillingness to entertain a conclusion inimical to the industry's interests when they dismissed the bad news in a report of a 14-year, $15-million research project on smoking and health that had been conducted by a committee of the American Medical Association with tobacco-industry funds. They have, in other words, long since debased the currency of their own arguments, so that their assaults on other aspects of the federal government's anti-smoking campaign cannot be taken seriously. We do not conclude from this that the government's effort is wise in every respect, only that the industry and friends have forfeited an important opportunity they might have seized somewhere along the line to help guide that effort in intelligent, prudent ways.

The the government should not remain neutral on the question of cigarette smoking seems self-evident and beyond argument to us. And Mr. Califano, given his particular responsibilities, is surely right in making the health effects of smoking an HEW issue. But the techniques the federal government should employ in trying to discourage cigarette smoking are not sself-evident at all. Some extremely delicate questions of government's proper role in the individual's affairs and of economic pressure and dislocation are raised. These, not the propriety of Mr. Califano's concern or the validity of the medical-research results, are what the tobacco industry would be worrying about and addressing itself to -- if it were even a little bit serious about trying to resolve this thing in a humane, responsible, public-spirited way.