C'mon, be honest. Which would you rather eat, an Oreo or something called a Fruit and Nut Oat Bran cookie?

Really? You don't want the Oreo because it has too many calories and you're on a diet and you have to watch your fat and blah, blah, blah?

Well, surprise, surprise, Hydrox hips. That oh-so-healthy oat bran number has virtually the same number of calories and fat as the ever-popular Oreo, America's top-selling cookie. In fact, if you pay a visit to your friendly neighborhood cookie aisle, you will see all kinds of so-called healthful cookies that have the same amount of fat as many regular cookies -- and sometimes even more calories.

A Nabisco Oreo, for instance, has 50 calories and 2 grams of fat -- 20 calories less and the same amount of fat as a Pepperidge Farm Wholesome Choice Apple Oatmeal Tart cookie, and virtually the same as Health Valley's Fruit and Nut Oat Bran cookies. And, if you check the label of Nabisco's Fat Free Fig Newtons, you will discover that while they have no fat, they also have 10 more calories than regular Fig Newtons, which had only one measly gram of fat to begin with. (And the fat-free kind aren't such an economic bargain either: A 12-ounce package costs more per ounce than a 16-ounce package of the regular newtons.)

And then there's the little matter of taste. To New Jersey dietitian Robyn Flipse, some of these new low-fat brands make her want to toss her cookies. "They're closer to a cracker or stale bread," she contends. "They don't have the flaky, melt-in-your-mouth quality of a cookie."

But the lure of a "no fat" label is a strong one, and food companies know it. In addition to no-fat newtons, Nabisco scrapped the fat from its Devil's Food Cake cookies. And guess what? Consumers have swallowed it. Since August, when the no-fat cookies were introduced, under the SnackWell's label, shoppers have wolfed down $55 million worth -- even though the original Devil's Food Cake cookies have just 1 gram of fat apiece.

The response is something Nabisco "never expected," according to a company press release -- and Nabisco is having trouble keeping supermarkets supplied with the soft chocolate cookies.

"We've had reports of consumers following our delivery trucks, and in Florida a club formed where the women go out and buy up whatever supply they can find and then split it among the members," says company spokesman Mark Gutsche.

However, some consumers may have realized that there is little fat difference between the two versions because Gutsche says sales of the regular Devil's Food Cake cookies are also on the rise.

Cookies aren't the only product going after the big profits in little fat. Low-fat foods have exploded in the past five years. "It's amazing," says Lynn Dornblaser, publisher of New Product News. Five years ago, just 275 new low-fat foods were introduced. Last year the number was 1,257. "It was also the first year that there were more new low-fat foods introduced than low-calorie," she notes.

One of the reasons for the manufacturers' fat-free frenzy is the decline in cookie consumption among aging baby boomers with widening waistlines, according to David Weiss, president of the New York research firm Packaged Facts. Boomers, he says, "faced the tough choice of whether to cut down on sweets or buy larger-sized clothing." When the cookies crumbled, manufacturers rushed to look for ways to woo these adult customers back.

Health Valley and Entenmann's rolled out fat-free products, followed by Pepperidge Farm's low-fat Wholesome Choice line in 1991 and Nabisco's SnackWell's line last summer. Pepperidge Farm spokeswoman Liz Gabriel describes the products as "cookies for people who didn't think cookies fit into their diet."

Not all nutrition experts are convinced, however. Washington dietitian Melanie Polk says low-fat cookies often replace fat with additional sugar. As a result, the calorie counts remain the same as, or even higher than, the original version.

Besides, she scoffs, what's the big difference between eating two cookies that have no fat or two cookies that have just 2 grams of fat? Not much when compared to the total amount of fat you have scarfed down all day.

"The problem is not in the product, but in the behavior of people," adds Flipse. "Eating six Frookwiches {a 50-calorie, fruit-juice-sweetened chocolate sandwich cookie} is just as bad as eating six {50-calorie} Oreos."

Flipse believes that most people seek out a lower-fat cookie so they can eat more of them. "But you have to ask yourself, 'Will it really satisfy me?' Will you walk away feeling you had a treat or feeling deprived?"

Her advice: "Have whole-wheat toast for breakfast instead of a muffin," Flipse says, "and use the fat and calories you save to have a real cookie."

Washington dietitian Melanie Polk offers these tips for those who want to have their cookies and eat them too:

There are many old-time cookies that are quite low in fat and also cost less than the heavily marketed new low-fat brands. Try munching a few of these: animal crackers, graham crackers, vanilla wafers, Teddy Grahams, lemon wafers and ginger snaps.

Look at lesser- known brands for low-fat bargains. FFV makes a Devil's Food Trolley Cake cookie that has 1 gram of fat and is similar to (and lower in cost than) both the fat-free and the regular Nabisco Devil's Food Cake cookies.

Read the label for fat content and check the serving size. Teddy Grahams, for instance, are low in fat and calories -- unless you eat two handfuls of them. -- C.S.