An incorrect date was given yesterday for the expiration of a congressional moratorium on Food and Drug Administration action against saccharin. The moratorium, which prevents the FDA from banning the sweetener as a good ingredient, expires next April.

The makers of Pepsi-Cola announced yesterday that they will drop saccharin from their diet soft drinks and begin sweetening the products entirely with the new low-calorie sweetener aspartame.

The announcement is a major commercial breakthrough for G. D. Searle & Co., the developer of aspartame, which it sells under the trade name NutraSweet. The Pepsi action could lead to similar moves by Coca-Cola Co. and Seven-Up, which yesterday said they were evaluating the situation.

For the past year, the major soft-drink makers have been sweetening their diet drinks with a blend of four to five parts saccharin to one part aspartame. Saccharin is far cheaper than aspartame, but has been found to cause cancer in laboratory animals.

PepsiCo Inc.'s decision to sweeten Diet Pepsi, Pepsi Light and Diet Pepsi Free with aspartame comes even as questions continue to be raised about the sweetener's safety.

Yesterday, the federal Centers for Disease Control suggested a new set of clinical studies of aspartame by the Food and Drug Administration because, while a recent CDC study found no evidence of "serious, widespread, adverse health consequences" from its use, there have been complaints about problems ranging from headaches to stomach upset to mood changes. The FDA approved aspartame for human use three years ago after what has been described as the most extensive testing ever done on a food additive.

Saccharin was nearly banned by the FDA for health reasons in 1977, and with the recent expiration of a congressional reprieve given the ingredient at the time, the agency could act at any time to take the sweetener off the market. Meanwhile, Abbott Laboratories, the maker of cyclamates, the sweetener that was banned for health reasons in 1969, has long had an application for reapproval of that product pending before the FDA.

Just before aspartame was approved for use in soft drinks last year, Pepsi and the other soda makers asked the FDA to delay the approval because of questions about health and the ability of the ingredient to stay sweet at high temperatures and over long periods of time. Many analysts saw the request as a ploy to win more favorable pricing of the ingredient from Searle, and the soft-drink makers soon dropped their efforts to delay its introduction.

At PepsiCo's announcement in New York yesterday, there were few indications of concern over the questions that had been raised two years ago. "Saccharin is out and NutraSweet is in," said Roger Enrico, president of Pepsi-Cola USA, PepsiCo's domestic operation. "We believe saccharin is safe. . . . We wanted the taste improvement in our products."

Enrico said consumer tests showed that Diet Pepsi sweetened entirely with aspartame was preferred by 2 to 1 over Diet Pepsi made with the aspartame-saccharin blend. Many people find that saccharin leaves a metallic aftertaste, although some complain that aspartame tastes too sweet. Aspartame is 200 times sweeter than sugar.

Pepsi will begin selling diet colas with 100 percent aspartame sweetening immediately, and expects to have them available in most of the nation by the first of the year.

Although aspartame is several times more expensive than saccharin or sugar, Enrico said Pepsi will not raise its prices to reflect the new ingredient.

Soda makers at first used a blend of aspartame and saccharin because of the increased costs, difficulties in obtaining supplies, and fears about how consumers would react to the new taste.

But aspartame-sweetened drinks, as analysts had expected, have given new impetus to the already fast-growing diet soft-drink field. Enrico said Diet Pepsi sales have increased 30 percent since the company began using the aspartame-saccharin blend, and analysts give the sweetener credit for attracting millions of new diet soda drinkers to swell diet sodas' share of the $25 billion soft-drink market to about 20 percent.

Pepsi officials expect diet drinks to capture one-third to one-half the market by the end of the decade -- up from 9 percent 10 years ago. The third-largest-selling soft drink in the nation, after Coke and Pepsi, is a diet soda, Coca-Cola's Diet Coke, introduced only 2 1/2 years ago.

Enrico said Pepsi has signed a new contract with Searle to buy five times as much aspartame as it has been buying.

Neither company would discuss details of the contract, but analyst Nelson M. Schneider, who follows Searle for E. F. Hutton & Co., said Pepsi is already buying about 10 percent of Searle's aspartame production of 7.5 million pounds a year, at a price of about $50 million.

The diet soft-drink industry is the biggest user of low-calorie sweeteners. Searle had been expected to sell $1 billion worth of aspartame next year even without Pepsi's action, with about half the revenue coming from soft-drink makers.

Searle already is selling virtually all the aspartame it can make, and Pepsi's additional supplies probably will come from a new plant Searle plans to open in Georgia in January, Schneider said.

Because of the tightness of supply, he said, Coca-Cola and Seven-Up could find themselves at a disadvantage if they decide to make a similar switch from saccharin. "Pepsi may have preempted the marketplace," he said.

The Pepsi announcement could also be a boon to two local biotechnology companies -- Genex Corp. of Rockville and Purification Engineering Inc. of Baltimore -- that supply the two amino acids that are combined to make aspartame.

Pepsi's announcement bodes less well for the makers of saccharin, Sherwin-Williams Co. and a number of Japanese and Korean companies. A spokeswoman for Sherwin-Williams, which in the past said it welcomed aspartame as representing a possible expansion tool for the entire low-cal sweetener market, downplayed Pepsi's announcement, saying that saccharin represented only a small part of the company's revenue.