The screaming for ice cream echoing through supermarkets these days has a decidedly lower pitch.

"The great trend is away from the high-fat products. It doesn't seem to be slackening at all," says Vern Hydorn, vice president of sales and marketing for Hood Ice Cream. Hood Light is starting to run neck-and-neck in sales with its regular ice cream.

The International Ice Cream Association's most recent sales figures show that supermarket sales of ice cream didn't budge between 1987 and '88. On the other hand, ice milk sales skyrocketed by 46 percent, and frozen yogurt almost doubled.

This has meant a wide array of pint, quart and half-gallon containers with less fat and more questions. Like an ice cream cone on a hot and humid day, the differences between the names and varieties can get sticky. The freezer case is jammed with alternatives: Which are lower in fat? What does "93 percent fat-free" mean? How do frozen yogurts stack up against ice milks? And what does "light" signify?

Currently, the government sets parameters for fat in sherbet, ice milk and ice cream. In the past few years, however, manufacturers have come up with a number of products that may fit into the same category but differ widely, and others that don't fit anywhere. Furthermore, there is no definition for the amount of fat in nonfat or low-fat frozen yogurt nor has "light" (or "lite") been defined.

A number of clarifying petitions are pending at the Food and Drug Administration, but in the meantime, "the whole dairy industry is up in arms about this," according to Jay Snelgrove, assistant for research and development at Ben & Jerry's Ice Cream. "What is light? It's scary for us. We don't know where we are when it comes to labeling."

If it's scary for the manufacturer who names the product (Ben & Jerry's Light), to the consumer looking for a summer refresher it is even more frightening.

As a guide to the supermarket freezer case, frozen desserts can be divided into the following categories, from the lowest in fat to the highest. Depending on the amount of fat added by flavoring (nuts, chocolate, etc.), some products may spill into another category.

Little or no fat: A smattering of dairy-based products using gums and gels to replace most of the fat has recently joined sorbets in this category of desserts containing less than one gram of fat per serving. Kraft's Sealtest Free fits here, and two of Edy's American Dream flavors contain less than one gram of fat per three-ounce serving. The remaining seven have one gram. American Dream is nevertheless called a "nonfat frozen dessert," which is OK according to the FDA because there is no definition for a nonfat frozen dessert. Simple Pleasures, which contains the newly approved fat substitute Simplesse, also has less than one gram of fat per serving.

Low fat: Overlap and confusion reign in this group, which includes frozen yogurts and most ice milks, many of which call themselves "light" or "superpremium." In fat and calories, frozen yogurts (made from cultured milk) and ice milks (made from regular milk) can be identical, so compare the nutrition information on the package. Using vanilla as an example, such products can range from one or two grams of fat per serving (Breyer's Lowfat Frozen Yogurt and Giant's Ice Milk) to three grams (Giant Light, Yoplait Frozen Yogurt, Lucerne Light, Lucerne Frozen Yogurt, Elan Premium Frozen Yogurt and Hood Light) to four grams (Breyer's Light and Brice's Frozen Yogurt).

Medium fat: Regular ice creams such as Safeway's and Giant's store brands, Breyer's and Edy's Grand belong in this group, ranging from about six to 11 grams of fat per serving, depending on the flavor. Be forewarned that the six flavors in Ben & Jerry's Light collection range from seven to 11 grams of fat per serving, just about the same as regular ice cream.

High fat: These are the super-premium ice creams, such as Fru sen Gladje, Ben & Jerry's, Ha agen Dazs, Giant Gourmet and Lucerne Gourmet. For vanilla, these can top out at 19 grams of fat per serving and more luxurious flavors can go even higher.

Two other categories would include nondairy frozen desserts (such as Tofutti), which are made from hydrogenated vegetable oil but still contain plenty of sugar, calories and fat (albeit unsaturated). Still, they may be useful for lactose-intolerant individuals. Sugar-free frozen dairy desserts such as Edy's Frozen Dietary Dessert and Sweet 'n Low Lowfat Frozen Dairy Dessert do have fat but are options for diabetics.

Confusion with all these frozen dessert categories stems only in part from a lack of definitions. How the government divides and defines frozen desserts does not correlate with the nutrition panel on packages.

The government's definitions for ice milk (2 to 7 percent fat) and ice cream (10 percent or more fat) are a measure by weight of the milk fat content. Consumers are more familiar with grams of fat per serving.

Nevertheless, many frozen dessert manufacturers pitch their products as being "97 percent fat-free," for example, which simply means that the weight of the milk fat is 3 percent of the total weight of the product. This is not a particularly useful or meaningful figure for a shopper, considering that most foods are made up primarily of water.

Jayne Hurley, associate nutritionist for the consumer advocacy group the Center for Science in the Public Interest, says she finds this especially misleading with ice cream bars. The 97-percent fat-free claim on the package of Klondike Lites applies to the ice milk product inside, not the whole, chocolate-covered bar, according to Hurley.

Tom Balmer, director of special programs at the International Ice Cream Association, says that percentage statements are "truthful and accurate," although the nutrition information panel is "the most relevant" to consumers.

Another obstacle to comparing products is the manipulation of serving sizes. Many frozen yogurt products list nutrition information for a three-ounce portion, rather than the four-ounce serving used for ice milks and ice creams. Thus, they come out with less than 100 calories per serving and the advantage in an unequal contest.

Robyn Flipse, spokeswoman for the American Dietetic Association, said she believes manufacturers do it "solely to have a more flattering calorie content as compared to other desserts they're trying to compete with. Everybody jerks that around to come out to their own advantage. It's the worst kind of deception."

When compared by the same serving size, some frozen yogurts are identical in fat and calories to ice milk. For example, per four-ounce serving, Brice's Frozen Yogurt and Breyer's Light ice milk (vanilla) each has 120 calories and four grams of fat.

The difference between two products of the same brand may be negligible. In a comparison of four-ounce servings of Safeway vanilla products, Lucerne Light ice milk has 110 calories and three grams of fat while Lucerne Frozen Yogurt has 107 calories and 2.6 grams of fat.

Who to blame?

"All the frozen yogurt products in the consumer market are three ounces. When a customer picks up our frozen yogurt and another, they can compare the three ounces," says Kimberly Staysa, spokeswoman for Edy's Grand ice cream. Edy's lists nutrition information in three-ounce portions on its American Dream and Frozen Yogurt Inspirations and in four-ounce portions for its Edy's Grand Light and Edy's Grand. Staysa says the three-ounce portions are not used to shed a beneficial light on the yogurt and nonfat products.

In general, however, consumers should watch their serving sizes when they dig into a pint or half gallon of a frozen dessert, says Flipse, who says she has clients who readily confess to eating a whole pint of Ben & Jerry's Light. A four-ounce portion, the size of a Dixie cup and one-quarter of a pint, is pretty small for most Americans, says the dietitian.

Instead, Flipse recommends controlling the size of the serving dish. Rather than using a cereal or salad bowl, try a four-ounce wine glass, a tea cup or a condiment dish. "Pamper yourself in a luxurious way," she says. "But you've got to know where to stop."