The mere mention of buttermilk provokes a frenzy of face-making and throat-clutching. It's the cod-liver oil of the dairy case.

You probably think of buttermilk, if you think of it all, as something to make fun of, like prunes and fishsticks and hot Dr. Pepper.

"The best use of buttermilk . . . ," a book called "The English House-wife" advised in 1631, "is charitably to bestow it on the poor neighbors . . ." Remember Little Miss Muffet's curds and whey? They were made out of buttermilk. (The idea that somebody would prefer curds and whey to anything else is pretty disgusting in itself.)

But buttermilk has never suffered such low esteem as today.

In a 1974 survey of food preferences among armed-services personnel, buttermilk came in No. 378 -- last -- behind such tempting dishes as pickled beet and onion salad (No. 361), mashed rutabagas (No. 374) and fried parsnips (No. 376).

Not even the trend away from whole milk -- low-fat milk now accounts for more than a quarter of all milk sales -- has been able to pull buttermilk out of its nosedive.

True buttermilk is a homemade farm product, a byproduct of making butter from cream. When the butter is drained from the churn, it leaves a residue called buttermilk.

Today, however, you're more likely to find a churn in an antique shop than on a farm. Store-bought buttermilk is typically skim milk (which used to be thrown to the hogs) that has been "cultured" with an inoculation of bacteria such as streptococcus lactis. Some dairies add a few flecks of butter to make it look churned.

The sour, tangy taste of cultured buttermilk comes close to the real thing, which no doubt strikes some people as a perverse striving for verisimilitude.

Nutritionally, however, there's no denying that buttermilk is the ideal dairy product. And cultured buttermilk, oddly enought, has it all over the genuine article in calcium and other nutrients.

Russian noblemen traditionally took the buttermilk cure for overweight and digestive troubles. One cup contains only 90 calories. It's high in protein, low in fat. Because of its acidity, it keeps well. And much of its lactose is converted into acid -- a big plus for people who suffer from sensitivity to milk.

"It'll make the hair on top of your head wavy and curly," says John Burn, president of a North Carolina dairy. Unfortunately, research in that area remains sketchy.

Buttermilk, even its advocates acknowledge, is what you'd call an acquired taste.

That says it -- Americans today aren't interested in having to learn to like anything, especially something that's gloppy, funky and good for you.

A comedian once noted that the worst thing about buttermilk is looking at the glass afterward. (That gloppiness, incidentally, is known in the industry as the viscosity factor.)

Nobody has to learn to like Cokes or french fries or Milky Ways.

Buttermilk's biggest handicap may be its lack of sugar. "Yogurt never did anything, either, while it was plain," says Dr. Gerald Quackenbush, vice president of the National Dairy Council.

In Europe, which has long appreciated cultured-milk products, buttermilk comes in strawberry, pineapple, cherry and chocolate flavors. "There is presently little demand for such products in the United States," the dairy council notes dryly.

Simple foods such as buttermilk seldom can hold their own these days with the deluge of heavily promoted -- and highly profitable -- processed foods.

The dairies, alas, haven't pushed any kind of milk for years, which helps explain how orange juice has recently become the drink of choice at the American breakfast table. "The dairy industry," says Quackenbush, "has written off milk, period." The profits lie in items like ice cream, cottage cheese and yogurt.

Buttermilk isn't going to disappear soon. But as more dairies drop out, eventually only one will be making all of it for one region (and processing it under other labels). A good example of this phenomenon is whipping cream, which has nearly succumbed to competition from aerosol products and whipped toppings.

The closest buttermilk ever came to show biz was when it lent its name to Dale Evan's horse. What if somebody had reported seeing Hamilton Jordan tossing down a shot of Churn-O at Studio 54? That would really have hurt his image.