Proctor & Gamble likes to portray its new synthetic fat substitute, olestra, as a dieter's dream. Imagine, something that tastes like fat but has no calories.

Well, judging from Procter & Gamble's own studies, it's clear that for many people the dream will turn out to be a nightmare. Those studies prove that olestra has two nasty habits:- In short term, ordinary amounts of olestra sometimes cause stomach cramps, diarrhea, and other gastrointestinal symptoms, which are sometimes severe.

- Over the longer term, olestra robs the body of nutrients called carotenoids that are thought to protect against cancer and heart disease.

Moreover, in two markets over the past two years, more than 2,000 consumers filed complaints about gastrointestinal symptoms that they experienced soon after eating Procter & Gamble's Fat Free Pringles or Frito-Lay's Wow chips, both made with olestra. Some people were doubled up in pain because of cramps (one woman said they were worse than labor pain); others had diarrhea and couldn't get from a business meeting or laundry room to the toilet in time. For still others, their cramps or diarrhea was so severe that they had to go to the emergency room. All that, apparently, from eating potato chips!

Procter & Gamble claims that all those bouts with olestra are purely a coincidence and that new research demonstrates that olestra is perfectly safe. While the company's glib explanations may sound plausible, the experts aren't fooled. Elbert Whorton, professor of epidemiology and biostatistics at the University of Texas Medical School, says that the new studies are not sensitive and that the FDA should retain the label notice.

Ironically, the people who experience severe gastrointestinal symptoms may be the lucky ones. If they link olestra to their effects, they'll probably avoid olestra in the future. It is the people who don't experience symptoms that are at risk, because olestra silently, imperceptibly steals nutrients they think they're getting from fruits and vegetables.

Two leading olestra critics, Walter Willett, chairman of the nutrition department at the Harvard School of Public Health, and Meir Stampfer, an epidemiologist in that department, have told the FDA that the nutrient losses resulting from widespread use of olestra in snack foods might cause several thousand cancer and heart disease deaths annually.

Dr. John Potter, a cancer expert at Seattle's Fred Hutchinson Cancer Research, says, "For olestra, the harm appears substantial. I . . . urge people not to buy Wow chips and other olestra foods."

Dr. Tim Byers, a professor of preventive medicine at the University of Colorado Health Sciences Center, recommends that olestra-containing products come with a warning label stating" "Do not eat this product with food."

Olestra, of course, has its defenders, including two former secretaries of the U.S. Department of Health and Human Services and the American Dietetic Association - but those and practically all other defenders are P&G paid consultants or grant recipients.

In the coming months P&G plans to buttress "expert" opinions with an estimated $100 million worth of advertising in a blitzkrieg to persuade the public that olestra is not just safe, but also healthful. It is safe to predict that none of the ads will admit what product labels are forced to disclose: "Olestra may cause abdominal cramping and loose stools."

When you see the slick ads portraying olestra as a godsend to an obese nation, just remind yourself to buy some tasty, perfectly safe baked chips instead and not to buy Tide detergent, Folger's coffee, Ivory soap and other Procter & Gamble products.

If you do eat olestra and your gastrointestinal tract throws a tantrum, call 1-888-OLESTRA to report your symptoms. Then tell your friends and neighbors just how glorious not eating olestra is.