Just in time for spring dieting, three artificial sweeteners -- aspartame, saccharin and cyclamates -- are in the news. Last week, a Senate panel rejected an amendment requiring labeling on soft drinks containing aspartame. This week, Congress considers whether to keep saccharin on the market. Meanwhile a National Academy of Sciences committee is reviewing the health effects of cyclamates, which were banned in 1970 because of a possible link with cancer.

Despite growing scientific evidence that aspartame causes alterations in brain chemicals and may change behavior, the Labor and Human Resources Committee defeated an amendment requiring soft drinks containing aspartame to list the amount of the chemical on the package.

Aspartame, marketed under the trade name NutraSweet by G.D. Searle and Co., is used in a variety foods and beverages, ranging from diet soft drinks to the table sugar substitute known as Equal. Products containing NutraSweet carry a label warning people with the genetic disease phenylketonuria (PKU) to avoid these food and beverages. PKU sufferers are born lacking an important enzyme that allows them to digest the amino acid phenylalanine -- a building block of protein and an important constituent of NutraSweet. PKU infants who consume phenylalanine become severely brain-damaged, and thus must be placed on a restricted diet for the rest of their lives.

Studies in humans and in animals suggest that aspartame can cause changes in neurotransmitters -- the chemical substances that send messages throughout the brain. These changes are particularly pronounced when aspartame is consumed with carbohydrates. Among the health effects associated with aspartame consumption are headaches and behavioral changes.

The FDA has established guidelines that suggest limiting aspartame consumption to 50 milligrams per kilogram of body weight. A kilogram is equal to 2.2 pounds. This means that a 25-pound child (about 11 kilograms) should consume no more than 550 milligrams of aspartame a day -- about the amount in four cans of diet soda.

Without labels describing how much aspartame is included in a product, "it is difficult if not impossible for the patient or his physician to know how much aspartame he has eaten or drunk," Dr. Richard Wurtman, a professor at the Massachusetts Institute of Technology, reported at a recent hearing before the Labor and Human Resources Committee. "I doubt that one consumer (or physician) in a thousand now realizes, for example, that a can of Tab provides less than one fourth as much aspartame as a can of Diet Pepsi or Diet Coke."

"Although we've made some progress with further NutraSweet and saccharin tests, we still have not fully protected the health and rights of consumers," said the amendment's sponsor, Sen. Howard M. Metzenbaum (D -- Ohio).

"I believe that it is essential that companies which include aspartame in their products be required to indicate on the labels how much of the sweetener is present in each can or serving," adds Wurtman, who says he uses aspartame himself. "I think that it would be very good to have labeling of all artificial sweeteners."

A spokesman for Searle said that the company is not "against labeling if it appears on all food products. We thought it would be unfair to single out just NutraSweet."

"It is a very safe product. NutraSweet is the most tested product on the market today."

Other recent scientific evidence suggests a link between the development of nonmalignant skin lesions and the consumption of aspartame. Research also suggests headaches and perhaps even high blood pressure can result from combining aspartame with certain medications.

One study published in the Annals of Internal Medicine described how a 22-year-old woman who drank daily 36 to 44 ounces of an aspartame-sweetened diet drink developed skin lesions on her thighs. Controlled tests over a period of weeks documented that the woman's lesions disappeared and reappeared with the use of aspartame. Two other reports published earlier this year in the American Journal of Psychiatry and the British journal Lancet document behavioral changes among aspartame users.

Cylamates could again become a choice for dieters and diabetics. A National Academy of Sciences committee is currently reviewing the scientific literature regarding the banned artificial sweetener -- at the request of the Food and Drug Administration (FDA) -- to help determine whether it causes cancer. The committee is expected to report its findings in June. If the scientific evidence is inconclusive, then the committee will design research that could answer the safety question of cyclamates once and for all.

Saccharin could soon be banned if Congress refuses to extend the most recent moratorium on prohibiting saccharin sales, which expired Monday. In 1977, despite evidence that saccharin caused bladder cancer in rats, Congress passed a law that allowed it to remain on the market. But FDA Commissioner Frank Young told a congressional committee recently that even if the moratorium is not renewed this week, it would take between six months and a year for saccharin to be removed from the market.