THE FOOD AND DRUG Administration's proposed ban on saccharin in food and beverages has been greeted rather sourly here and there. The FDA's action and a broader ban proposed in Canada were prompted by a Canadian study that linked the no-calorie sweetener to bladder cancer in laboratory rats. The findings have been ridiculed because the rats were fed such large amounts of saccharin that a human being, to ingest a comparable dose, might have to drink 800 diet colas per day, or chew 6,700 sticks of Blammo gum daily, or consume 1.5 million packages of Sweet'n Low per year. Such outlandish figures are supposed to show that any risks are so minute, even for saccharin junkies, that the ban is unwarranted. Moreover, it is argued that barring saccharin will complicate diet controls for diabetics and could lead many people to increase their consumption of sugar, with many adverse effects on health.

It may well be that the average weight-watcher is not too likely to contract cancer from using saccharin. However, the doses used in the Canadian study are well within the range that cautious toxicologists like to test before deciding whether a substance is safe. Moreover, "likelihood" is not the proper standard to apply. Under the Delaney amendment, the FDA is required to act against any substance shown to cause cancer in humans or animals, no matter how remote the risks may seem. There is good reason for the uncompromising language of that law. Defining acceptable risks to public health is a devilish job even, if all the evidence is in. The effects of repeated exposure to carcinogens, especially in small quantities, may not show up for 20 years or more.

The weighing of risks does become rather different for diabetics and others for whom strict diet or weight control is a daily medical imperative. Those cases can be handled by keeping saccharin available as a prescription drug, which the FDA could do. The sweetest note in the whole situation, though, is that many of the food and beverage manufacturers are now pressing ahead with their usual ingenuity to develop substitute sweenteners, much as they did when cyclamates were banned. We only hope the new concoctions will be thoroughly tested before they are marketed - not afterward. Meanwhile, it won't be tragic if there is a little less no-calorie sweet stuff in the marketplace. There is, after all, another substitute for sugar. It is called self-discipline, and it is generally considered very safe.