Twenty-five years ago, on Jan. 11, the U.S. Surgeon General dropped a bombshell on the tobacco industry and the smoking public - throwing the weight of the federal government behind a flat declaration that smoking was a hazard to health. Although tobacco companies bitterly fought the findings for years, the evidence against smoking has kept piling up.

In the quarter century since, there has been a quiet revolution in the once deeply ingrained public cigarette habit. Public attitudes toward smoking have changed dramatically.Successful campaigns have been fought at all levels of government to ban or restrict smoking in public buildings, the workplace - some companies won't even hire smokers - restaurants, airplanes, buses, and trains.

Cigarette ads, once a mainstay of television commercials, have been banned from TV altogether, and health hazard warnings are including in all cigarette ads in printed publications, and the cigarette packages themselves.

The aura of sophistication surrounding smoking has vanished and it is the poorer, less educated who now are the biggest segment of the smoking public. Less than one in five college graduates smokes, while more than a third of those who didn't finish high school are smokers.

The percentage of smokers has declined steadily until tobacco users are a distinct minority - less than 39 percent of the population. Using cigarettes was once strictly a male habit, but now only 27 percent of American men smoke, less than women.

An estimated 35 million persons have quit since the surgeon general's report appeared and another 1.3 million quit each year. Unfortunately, one million young people take up the habit each year, and smoking remains the number one preventable cause of death in the United States.

More needs to be done to inform young people and the less educated about the dangers of smoking. It still kills an estimated 390,000 Americans annually. If youth can be reached effectively, the nation may yet realize the prediction of the current surgeon general, C. Everett Koop, of a smokeless society by the year 2000.