EDITORIAL : BON APPETIT WHAT YOU DON'T KNOW ABOUT THANKSGIVING DINNER PROBABLY WON'T HURT YOU.

IT'S common knowledge that traditional Thanksgiving dinners can be fattening.

Now for some information that may be less widely known: According to the private American Council on Science and Health, a typical Thanksgiving dinner - including soup (cream of mushroom), a relish tray (carrots, tomatoes and celery), turkey and dressing, baked potatoes, sweet potatoes, rolls and butter, coffee, tea, etc. - contains numerous chemicals that are carcinogenic, toxic or mutagens (potentially harmful to genetic material).

Now don't be alarmed. A traditional Thanksgiving dinner with all the fixin's isn't unhealthy. The council is just using it - as it does each year - to illustrate the contradictory, if not absurd, nature of some federal Food and Drug Administration regulations.

(While naturally occurring carcinogens, such as those in a Thanksgiving dinner, don't bother the FDA as long as they are in natural foods, even trace amounts are barred in food additives.)

One of the council's pet peeves is the way that the feds determine what is carcinogenic: stuffing laboratory rats with enormous amounts of suspect substances and waiting to see what happens. The council observes - taking into account the differences in weight between humans and rats - that a person would have to eat 82,600 slices of bread a day to equal the amount of furfural that increased the risk of cancer in luckless rodents.

More to the point, the council says, are tests showing that ``overfed rats get cancer more often than normally fed rats.''

That's useful information for people, too - especially on Thanksgiving. So go easy on the seconds Thursday.