Fran Hardter has stopped buying pesticides, bologna, bacon, aerosols, disinfectants, deodorant soap, laundry brighteners, leaded gasoline, and is feeling guilty about her schnauzer's flea collar.

The flea collar contains a pesticide, but what are you going to do?" she asks. "We tried to do without the flea collar," but the dog "pulled his fur off in places trying to get at the fleas and ticks."

Fran and Ross Hardter, both deeply involved in environmental causes in Northern Virginia, are concerned about what they feel are the real and potential hazards that enter their lives in a myriad of ways: in food and materials, in the water and air. "We are surrounded by an ocean of carcinogens," Mrs. Hardter says.

"But," she emphasizes, "you can't avoid everything. You're go crazy."

In 1976 alone, The Washington Post carried stories linking cancer causing agents to various drugs, sex hormones, beef, chicken, swine, turkey, over-the-counter medications, cough syrup, toothpaste, food packages, sleepwear, snuff, quarries, X rays, herbicides, pesticides, decafeinated coffee, beacon, red dye No. 2, various workplaces, air and drinking water.

"There has been an explosion of knowledge," said Dr. Ruth BeilerWhite, who heads the consumer inquiry staff at the Food and Drug Administration. And in a steady stream of letter, Americans are telling the FDA that they - like Mrs. Hardter - are fearful that they are surrounded by cancer-causing substances.

Dr. Beiler-White thinks the concern is misplaced. "They should be worrying about malnutrition and food-borne (bacteria). People just don't have perspective," she said.

Some citizens have simply resigned themselves to eventual death from cancer as a result of something they ate, drank, touched or breathed. Dr. Hans Falk, associate director for health hazards in the National Institute for Environmental Health Sciences, described people he commonly encounters in his travels: "They feel that because of this type of continuous bombardment with chemicals, that because in the next five years they will have taken 25 new chemicals that, they think, will lead to their downfall, all they can do is sit back and be cooked."

This type of fatalism worries both consumer activists and federal regulators. Sidney Wolfe, director of Ralph Nader's Health Research Group, says, "We are concerned that people get frustrated and say everything casues cancer. But that's false."

In publishing its proposed rule to ban the artificial sweetener saccharin because it "poses a significant risk of cancer for humans," FDA Director Donald Kennedy made the same point. Kennedy said tests of 120 suspected chemcials showed only 11 of them produced tumors in mice at the maximum doses.

The problem is not that the regulators are faced with so many carcinogens but that for the limited number that exist, there is no known safe level. Scientists believe that extremely high doses of saccharin may cause cancer, but they don't know at what, if any, level saccharin will not produce any cancers of the bladder. In March, the FDA banned saccharin from all foods and beverages.

Scientists have determined, through statistical extrapolation but not actual studies of living persons, that if every American, consumed the amount of saccharin in one 12-ounce diet drink, each day "between 0 and 1,200 . . . cases of bladder cancer" would result. Because biostatisticians always lean toward the conservative estimate, the figure representing the maximum number of cases - 1,200 - is used to state the risk.

Scientists unable to determine safety thresholds for identified carcinogens. But even if they could there is no way, short of outright policing of people's eating and drinking habits, that the FDA could keep individuals from exceeding the daily limit that would keep them within the no-cancer range. Therefore the FDA banned saccharin from all food and beverages, saying it will consider permitting the artificial sweetener to be sold as an over-the-counter drug.

Many Americans were outraged. They seized on Commissioner Kennedy's estimation that humans would have to drink 800 cans of diet soda daily for the rest of their lives to get the equivalent of the maximum, dose given the laboratory rats that developed cancer.

Rep. Barbara A. Mikulski (D-Md.) called the tests with such massive dosage "ridiculous" and said anyone drinking even a small part of this amount "would die of gas before they would die of cancer."

And humorist Art Buchwald suggested that saccharin packages be labeled: "a recent test showed that 12 out of 44 white rats who were fed a fifth of their diet in saccharin found it hazardous to their health."

The saccharin ban has raised a furor of opposition. By contrast, there was an immediate demand for quick action when reports began to circulate that Tris, a chemical used as a fire retardant in children's nightwear, was a mutagenic - capable of altering genes. Powerful mutagenics are suspected of being carcinogenic.

Parents put pressure on the U.S. Consumer Protection Agency to act, and the agency banned the use of Tris in an children's nightwear. Robert Harris, who heads the Environmental Defense Fund, thinks people reacted quickly because children, who have a whole lifetime to get cancer, were affected.

The agricultural and food chemical industry warns that if stepped up regulation continues, food production will have to be drastically curtailed and choices in the supermarket will have to be sharply limited. Richard L. Hall, the additives expert at Mcormick and Co., the Baltimore spice maker, gives a prepared talk in which he tells assembled diners that their entire meal would have to be eliminated if everything on their plate were subjected to the same scrutiny as chemical food additives.

Fran Hardter, who has tried to eliminate all possible carcinogens from her family's diet, says that when she tried to give up cold cuts containing nitrites - preservatives and colorings suspected in the formation of carcinogenic susbstance - "the only thing left was chicken roll."

Readers of stories about the "explosion" of data on new carcinogens will find no reassuring consensus on what they should do. Industry spokesmen say many fears are either groundless or overdrawn. The FDA, even as it bans long-used chemicals, says Americans should be more concerned about other hazards such as malnutrition and food poisoning. Consumer advocates indict ever more substances as carcinogens, but, detecting a backlash of despair, tell people that only a small minority of chemicals are implicated.

Fran Hardter tries to eliminate from her house all the substances linked to carcinogens. It's a difficult task, though. She tried to eliminate cold cuts with nitrites - preservatives linked to carcinogens - but, she says, "the only thing left was chicken roll."