G. D. Searle & Co. said yesterday it has asked the Food and Drug Administration for permission to offer its low-calorie sweetener, aspartame, in soft drinks -- the largest part of the diet sweetener market.

"We have no indication that there will be any trouble getting it approved," said Richard McGraw, a spokesman for Skokie, Ill.-based Searle. Searle hopes to receive the approval within a year, he said.

The FDA has six months to ask for more information on the proposal, although that period can be extended.

McGraw said that because the FDA already has approved aspartame for other uses, the focus of the inquiry probably will be on such issues as the substance's ability to stay sweet under certain usage and shelf-life conditions.

A spokesman for the FDA said, "There shouldn't be any real problems" with the approval.

Aspartame, a natural sweetener made from amino acids, was approved by the FDA last year, 17 years after its discovery, after what is believed to be the most rigorous testing ever given a food product. Searle began selling it in powder form earlier this month under the trade name Equal. In bulk, its trade name is Nutrasweet.

Each new use for the product must receive FDA approval.

Searle had delayed asking for its approval as a beverage sweetener until the company could build up its manufacturing capacity for aspartame.

"This is obviously the largest single market for Nutrasweet," McGraw said.

Diet soda accounted for 7 million of the 11 million pounds of saccharin sold in the United States last year. Diet soda posted wholesale sales of $20 billion last year, about 15 percent of the U.S. market for soft drinks.

Searle claims aspartame is superior to saccharin because it has no aftertaste and is not suspected of causing health problems.

Aspartame already is being used to sweeten almost all major brands of soft drinks in other countries, particularly Canada, where aspartame-sweetened drinks hold 15 percent of the total soda market. Spokesmen for major soft drink producers here would not comment on their plans to offer aspartame-sweetened drinks in the United States.