The Food and Drug Administration approved this week a new no-calorie sweetener, called Sunnette, for use in chewing gum, puddings, dry mixes for drinks and in tablets and packets for the tabletop.

The product, known generically as acesulfame potassium, was discovered in 1967 by scientists with the Hoechst Celanese Corp. of Somerville, N.J. It is already being sold in 20 other countries, but a consumer group said it believes the product causes cancer in laboratory animals.The white powder, which is about 200 times sweeter than sugar, differs chemically from aspartame and saccharin, the two artificial sweeteners now on the market. Unlike the low-calorie sweetener aspartame, acesulfame potassium is not chemically based on amino acids. It is a cyclic organic molecule, that is, a ring-shaped molecule of carbon, oxygen, nitrogen, sulfer, and potassium, according to Pat McLaughlin, food safety officer for the FDA.

McLaughlin said she had sampled the product and detected no aftertaste or tastes other than sweetness.

Leon Starr, president of the research division and chief technical officer for Hoechst said the water-soluble compound is stable at high temperatures, unlike the other sweeteners.

Starr said the company is now preparing petitions to the FDA for permission to use the product in soft drinks and baked goods. He said the sweetener has no calories and is safe because it passes directly through the body without being broken down.

But the Center for Science in the Public Interest, a consumer advocacy group, had grave reservations: "Using established cancer principles, the case that acesulfame potassium causes cancer is strong," said Lisa Leffert, staff scientist for the group.

"In one study you see lung tumors, in another twice as many mammary tumors in test animals as in controls. You see effects increasing with dose, and you see significant results," Leffert said.

But a statement from the FDA said, "Detailed analysis of all the data, . . . including data from other studies using these strains of animals, showed that any tumors found were typical of what could routinely be expected and were not due to feeding with acesulfame potassium."

The agency said in its review of the safety data it "applied a 100-fold safety factor in making its safety assessment - that is, the agency found that the maximum amount consumed by humans would be less than one-hundredth of the amount that caused no toxic effect when fed to animals."

Starr said Sunette would be priced to be competitive with other artificial sweeteners, but was uncertain when it would be on store shelves. He said this depended largely on the interest of food manufacturers. "There may be some test marketing by the end of the year, but that's really speculative," Starr said. "I think you'll really see it in 1989."