It's lunch hour at the Yummy Yogart carry-out on M street. As usual, the joint is jumpin'. Secretaries, young executive types, students, tourists and others crowd the small store like so many assorted nuts in a can.

"I used to love ice cream," says John Noonan, a Post Office worker, as he carries a pint of strawberry yogurt to a table on the Yummy Yogurt patio. "In fact, I still do, but I try to stay away from it if I can. Last year I turned 35 years old, and I realized I'd better start taking better care of myself -- a better diet, more excercise. And less stuff like ice cream. Too much sugar and fat, you know.

Liza Kirwin, an archives technician at the Smithsonian, explains, "It's easy to substitute yogurt for ice cream.With yogurt, there's no guilt. You don't have worry about burning off ice-cream calories. In fact, when I do eat ice cream, I mush it up so that it has the look and consistency of yogurt."

Aficionados can be found not only at delis and carry-outs, but also in the halls of Congress. Senator William Proxmire of Wisconsin ("America's Dairyland," boosts the state's license plate) admit to being a yogurt fan. The senator, whose favorite flavors are strawberry, lemon, and blueberry, confides, "I avoid ice cream because of the sugar and the calories."

In each of these testimonies, one candetect more than just loyal devotion to a particular product. The above quotes, in fact, seem to contain a hint of chauvinism -- a prejudice against not just ice cream, but all foods that smack of fat, sugar, calories, fun.

Call it dietetic snobbery. Call it moral superiority. Call it what you want, but it's there.

Since, as the saying goes, we are what we eat, yogurt-eaters, by dint of their grandiose intake of "healthful" foods, apparently consider themselves mentally, physically and morally superior to the rest of us carnivorous, sugar-loving, finger-licking, soda-swilling wrecks.

Janet Denny, a University of Maryland teaching assistant who's been eating yogurt for five years, agrees that most yogurt devotees do indeed regard their kind as something like a beautiful sunflower amid a field of ragwee.

"It usually depends on the person," she says. "I used to work in a health-food store, and I would come across a lot of people who'd latch onto a cup of yogurt and say, 'Aha, now I'm healthy.'

"I guess there is a certain feeling among people who eat yogurt that theyRe healthier than those who eat so-called junk."

On the other hand, Liza Kirwin says that she doesn't "get the impression that yogurt-eaters feel superior, morally or any other way.

True, we're more self-conscious about our weight and health, but there's no real status to eating yogurt.

"People eat it because it tastes goodand because it's good for you. Maybe when Americans started eating it a lot about ten years ago, it was the chic thing to do. It was new, exotic.

"But now that mentality has been overridden by a few simple facts about yogurt: it's convenient, inexpensive and healthy."

Those few simple facts help explain why 567 million pounds of yogurt were consumed in the United States last year. According to Olga Olsen of the Milk Industry Foundation, that comes to about 2 1/2 pounds for every American.

(However, ice cream remains the champby far: 3 1/2 billion pounds of it were devoured in this country last year, an average of about 16 pounds per person.)

Most yogurtphiles profess to hate sugar as much as Dracula hated dawn. Still, as Daniell Schor, a nutritionist at the Diary Council of Greater Metropolitan Washington, points out, many people favor the flavored kinds of yogurt, which "have a higher calorie count because of the sugared fruit preserves at the bottom of the cup." And through the majority of yogurt-lovers are reformed ice-cream addicts (and proud of it), they fail to realize that, in the war oncalories, yogurt doesn't triumph by as large a margin as assumed.

A pint of flavored yogurt totals about 263 calories, a pint of vanilla ice cream about 300. Then there are those amusingly benighted souls who buy low-fat plain yogurt (150 calories per pint) and then heap on granola, nuts, fruit and other little doo-dads, sending the calorie count into the ionoshpere.

Schor advises the "People should have two servings from the milk group each day, which would include two 8-ounce servings of yogurt."

Is it possible to eat too much of thestuff? Is there such a thing as a yogurt overdose?

"No you can't really eat too much yogurt, unless you eat the flavored kinds and want to watch your weight. In that case, you should stick to plain yogurt and add nuts and fruits if you want to."

the question of yogurt overdoses brings to mind the study conducted by scientists at John Hopkins in 1970.The experiment, in which 30 rats ate nothing but yogurt for a month and developed cataracts, was quickly decried and disproved by the National Dairy Council. Yogurt-lovers everywhere, who had momentarily and fearfully dropped their spoons because of the study, reached for them once again, the reputation of their sacred staple rescued, their status as superior beings uncracked.

More's the pity. These people couldreally use a shot of humility, a tumble from their perch on I'm-OK-You-'re-Not-OK Mountain. Maybe tomorrow we'll read about a Harvard report showing that yogurt causes scurvy, or laughing sickness.

The only thing we yogurt-detrators can do is hope and wait for the mighty to fall. We'll continue eating our burgers and drinking our Dr. Peppers and munching our Milky Ways. And reveling in the mad delicious guilt.

In the meantime, all of us would do well to remember the words of Mark Twain: "Part of the secret of success in life is to eat what you like and let the food fight it out inside."