Last week, Health and Human Services Secretary Margaret M. Heckler gave preliminary approval to the irradiation of fresh frutis and vegetables to prevent spoilage and insect infestations.

Proponents of irradition say it is one way food can be preserved without using potentially cancer-causing chemicals. But critics say irradiation might endanger consumers' health by transforming some of the food's chemicals into potential carcinogens.

Although the new regulations only pertain to fresh fruits and vegetables, one day, industry experts hope, most foods will be preserved by irradiation. Irradiation already has been approved by the Food and Drug Administration for wheat, potatoes and spices, but it has proved uneconomical and has never been widely used.

To preserve food with radiation, the item is exposed to to gamma rays (which are similar to X-rays) emitted by radioactive materials. The radiation destroys food-borne bacteria.

Radiation is measured in units called rads. The FDA allows exposure of up to 100,000 rads for already approved foods. At this level, gamma rays penetrate the food and kill bacteria and other infectious organisms by preventing the organisms from dividing and growing. The food, however, does not become radioactive.

Some 441 scientific studies have analyzed the effects of radiation on food. And those studies have been the subject of hot dispute.

Those opposed to food irradiation cite 32 studies that purportedly show adverse effects of irradiation on food, such as the possiblity of creating cancer-causing chemicals in the food itself. But the FDA dismisses all but five of the 441 studies as scientifically flawed, and those five studies, the FDA said, show irradiated food is safe.

"A number of studies still need to be conducted," said Kathleen Tucker, executive director of the Health and Energy Institute, a Washington-based public interest group. "We don't believe the American people should be guinea pigs."

Industry and the FDA counter that the agency has ample information about irradiation. They say irradiation will enhance consumers' health by replacing hazardous post-harvest chemicals. It will also control diseases spread by eating meat tainted with parasites like trichinae or bacteria like salmonella.

"Irradiation allows us to eliminate toxic materials -- known carcinogens and mutagens" from foods, said Martin Welt, president of Radiation Technology Inc., in Rockaway, N.J. "We're going to revolutionize the food industry."

The concept of irradiated foods first reached the public when Soviet cosmonauts complimented American astronauts on the tastiness of their irradiated steak during the 1975 Apollo-Soyuz rendezvous. Now, after 40 years of research, it may soon be available in supermarkets.

Recently approved by the FDA to eliminate trichinosis parasite in pork, irradiation must also be approved by the Department of Agriculture before irradiated pork can be sold.

"It will probably take two years before it's an everyday event at the store," said FDA spokesman Jim Greene.

Irradiation has been on the regulatory fast track since last year, when. Heckler called it a safe alternative to the now banned pesticide ethylene dibromide or EDB.

Benefits of irradiation, which extends the shelf life of some foods, are often highly touted. Some claim it will be a boon to farmers by extending the life of produce for export. Others say it could increase the world's food supply. Still others talk of meat that stays edible for three weeks and strawberries that stay fresh for a month.

Irradiation will affect each produce item differently, said Dr. Donald W. Thayer, director of the USDA's Food and Safety Laboratory. While irradiation may delay ripening of mangos, papayas and bananas, it could accelerate ripening of sweet cherries, peaches and certain nectarines.

Irradiation can control insects like the Indian meal moth, codling moth and medfly in most produce and dried fruit. But not all produce, said Thayer, can be irradiated because some, such as citrus fruits and bell peppers, can turn mushy or brown.

Sen. Slade Gorton (R-Wash.) and Rep. Sid Morrison (R-Wash.) have proposed legislation that would redefine food irradiation, currently considered a food additive, as a "food process."

Unlike additives, food processes do not have to be listed on labels.

Tucker, from the Health and Energy Institute, which opposes the bill, said it is designed to protect sales, which might be jeopardized by cautious consumers. "Labeling could be avoided, making it easier to sell irradiated food," she said.

Gorton, whose state of Washington is home of the Hanford Nuclear Reservation, said: "It's much easier for the FDA to come up with regulations if it's able to treat irradiation as what it is -- a process. This bill is designed to reflect reality."

Food irradiation is used in 21 countries, including Britain, Denmark and Japan, and was first approved in some nations 20 years ago. Critics say, however, that not enough time has elapsed to know if irradiation will contribute to hazardous long-term effects.

In the United States during the '60s, the FDA approved irradiation to prevent potatoes from sprouting and to control insect infestation in wheat and wheat flour. But the process, more expensive than chemicals applied for the same purposes, was never used commercially for these products.

Although the FDA approved the irradiation of spices two years ago, only a small portion of spices, garlic powder and onion powder are commercially irradiated. The process is most frequently used to kill bacteria in cosmetics, hospital equipment, baby powders and astronauts' meals.

Critics of irradiation are concerned about the safety of eating irradiated food. Tucker and others raise questions about the loss of vitamins; increased production of naturally occurring "aflatoxins" (a carcinogen produced by certain fungi); creation of new chemicals or "radiolytic products" in food; and the increased risk of food poisoning by radiation-resistant botulism bacteria.

"Despite industry's protests that this has been studied to death, there's an insufficient number of studies," said Allen Greenberg, staff attorney for Public Citizen, a Washington-based consumer group that petitioned the FDA to withdraw, pending further tests, the proposal to irradiate produce. "It's just insane not to know more than we know now."

Several scientists have questioned the adequacy of existing studies and long-term safety of irradiated food. "We don't know it's safe. For the government to say they know it's safe is simply untrue," said Dr. John Gofman, professor emeritus of medical physics at the University of California at Berkeley. "I don't think people are going to drop over dead in 30 days -- my concern is the long-term carcinogenic potential."

But FDA officials say critics' concerns are unfounded and the agency has sufficient research about the safety of irradiated food. "Experts in toxicology, nutrition and radiation chemistry have looked at this all over the world, and regulators have unanimously concluded that irradiation is a safe process at these levels," said Sanford Miller, director of FDA's Center for Food Safety and Applied Nutrition. "People who are opposed to this get the issue confused with nuclear weaponry, bombs, and power stations. There doesn't have to be a nuclear plant in the world for a radiation business to operate."

Food products to be irradiated are put on a conveyor belt which travels through a shielded chamber, with walls of 6 1/2-foot thick concrete, where the products are exposed to gamma rays. The gamma rays are emitted from a radioactive source such as cobalt 60 or cesium 137.

The radioactive material is encapsulated in stainless steel casings, special rods called "pencils," which are 18 inches long and one quarter inch in diameter. When not in use, these pencils are stored beneath 15 feet of water. Some industry officials say that because of the steel casing, disposing of these pencils is safer than getting rid of toxic chemicals.

"Over time, disposing of pencils will prove to be infinitely less hazardous than disposing of chemicals," said George Giddings, director of food irradiation services with Isomedix, a New Jersey company that sterilizes medical equipment. "You're not going to have Love Canals because the material never passes through the casings."

But, according to a 1976 New Jersey newspaper, a pencil ruptured at the Isomedix Parsippany Plant, contaminating water and creating a waste disposal problem.

Accidents are not unknown to industry, according to the Health and Energy Institute. Those opposed to food irradiation worry about industry's safety record. Although hospitals have used radioactive materials safely for years, Tucker doubts whether the food irradiation industry will be as careful. "A cannery is just not run with the same kind of precaution as a hospital," she said.

Giddings, however, said he is confident about current safety precautions. "These plants are so designed for worker safety, that it's extraordinary any worker gets exposed," he says. "If you're just absent-minded, you can't hurt yourself -- it's only when someone deliberately circumvents the system."

Welt also said the food irradiation industry is safe. "It's got the safest workplace record of any industry," said Welt, whose company, Radiation Technology Inc., petitioned the FDA and received approval to irradiate spices and, more recently, pork.

Welt acknowledged his company is on the Environmental Protection Agency's Superfund list of hazardous waste sites, but said the designation is undeserved.

"Yes, we are on the Superfund list, but I doubt by any stretch of the imagination that we should be. The chemicals which are now in our ground water, have nothing to do with our operation." Welt said the contamination is a result of operations by the site's previous owner.

Radiation Technology Inc. was also fined and had its license temporarily suspended by the Nuclear Regulatory Commission in 1977, after a worker was exposed to excessive levels of radiation.

FDA official Miller, however, said he is more worried about the hype than the controversy of irradiated food.

"Irradiation is no magic potion. This is not going to revolutionize our food supply. It's another tool, that's all it is," Miller said. "My biggest concern is that irradiation is a solution that's oversold."