The powerfully concentrated low-calorie sweetener aspartame, a substance 180 times sweeter than sugar, was approved by the Food and Drug Administration yesterday for use in carbonated soft drinks.

Aspartame's manufacturer, G.D. Searle & Co., promptly launched a campaign to woo consumers away from sugar and saccharin. Saccharin is the only other low-calorie, non-sugar sweetener sold in this country, but many users complain of a bitter aftertaste. In July 1981 the FDA approved use of aspartame as a table-top sugar substitute and as an additive in drink mixes, instant coffee and tea, cereals, gum, gelatins, puddings, fillings and toppings. But the big potential market is in soft drinks, with sales in the tens of billions of dollars.

A Searle spokesman said no American drink maker has committed to using aspartame, which is currently used in Canada in some forms of Coca-Cola, Pepsi-Cola, 7-Up, Dr. Pepper and ginger ales, as well as in Diet Coke, Tab and other drinks. Canadian sales are "tremendous," the Searle spokesman said.

The FDA's action follows a decade of studies and quarrels, and overrides two recent objections to aspartame: one over its possible effect on the brain, and the other over whether the substance will keep in warm weather.

The agency discounted both concerns, saying its data has "confirmed the safety" of "one of the most tested food additives ever evaluated by FDA."

Robert Shapiro, president of Searle's Nutra-Sweet Group, yesterday called aspartame "an entirely new choice . . . that tastes great, has no aftertaste and no health concerns"--for diabetics or persons worried about tooth decay, for example. "We're at the early stages of getting it onto the market," he said, "but everything we know suggests consumers will respond very well."

The FDA acted slowly, even though one of its officials has called aspartame "the ideal food additive," with a mere tenth of a calorie's worth replacing an 18-calorie teaspoon of sugar and "no metallic aftertaste. It tastes a little perfumey alone, but when it's in something like lemonade, you can't tell the difference."

Aspartame is the first non-sugar sweetener the FDA has approved since it banned cyclamates as possible cancer-producers in 1970. Searle first sought approval of aspartame in 1973. The FDA approved it in 1974, but held up that approval after a scientist said animal feeding studies had resulted in brain lesions.

In 1977, meanwhile, the FDA tried to restrict use of saccharin as a "weak"--very occasional--cause of bladder cancer, but Congress has repeatedly blocked any such ban.

In giving aspartame its limited 1981 blessing, FDA Commissioner Arthur Hull Hayes Jr. overruled a scientific panel's recommendation for more animal studies.

Last month, Dr. Richard Wurtman of Massachusetts Institute of Technology said his findings indicate that, if consumed with carbohydrates (starches or sugars), a chemical in aspartame could inhibit an important brain chemical, the neurotransmitter serotonin. Wurtman called for more study, but the FDA said his data do not support his fears. "Moreover, aspartame has been used for about two years in soft drinks in Canada with no reports of ill effects," the FDA added.

The agency also revealed a request from the National Soft Drink Association to delay approval pending additional tests of whether aspartame will keep for more than a year in climates warmer than Canada's. The FDA said temperature may affect aspartame products, but proper shipping and marketing should protect them.

Analysts are uncertain how aspartame and saccharin will fare in the battle for the highly lucrative soft-drink market. For the most part, the major soft-drink companies have been noncommittal about their plans for using aspartame, in part because of its cost.

Sweetening 24 12-ounce cans with 100 percent aspartame costs $1.04; the amounts for sugar and saccharin are 55 cents and 3 cents, respectively, according to George Thompson of Prudential-Bache Securities.