A can of Campbell's Cream of Mushroom Soup was selling for 50 cents at a Giant last week. The company's Special Request version of the soup, with a third less salt, cost 55 cents. Campbell's Low Sodium Cream of Mushroom Soup was 59 cents. As the salt goes down,t he price goes up.

Whether it's Campbell's soups, Polaner's reduced-sugar preserves compared to the company's standard preserves or Kraft's lower-fat cheese products as opposed to its regular cheese products, less costs more. And consumers don't like it. "The sentiment is that they (shoppers) don't want to pay more for less," said Mona Doyle, president of Consumer Network, a market research firm that tracks consumer opinion on supermarket services and products.

Five or six years ago, when a proliferation of "lite" products entered the market, shoppers expressed their dismay "with increasing vigor" about paying more for less salt or sugar, fewer additives and/or preservatives, according to Doyle's newsletter, The Shopper Report. Many consumers didn't understand the discrepancies and others believed-them to be "price gouging on the part of manufacturers."

Whether or not it is worthwhile to pay more for less depends on the products, your health status, your tastes, the size of your serving and the size of your pocketbook.

In making the determination, the first thing to do is to examine what the product difference really is. Pay attention to what is actually being removed and whether its presence was a significant concern in the original product.

For example, Skippy Peanut Butter, which boasts having "less sugar" than other leading brands, cvost more -- at least at an Alexandria Safeway last week -- than three other brands (at Giant it cost the same).

The sugar reduction "is a false issue," says Bonnie Liebman, director of nutrition at the consumer advocacy group, Center for Science in the Public Interest. "There's not enough sugar in any peanut butter to make a difference."

Pay attention to serving sizes. Swiss Miss' Lite Hot Cocoa Mix, for example, may contain a third less calories than the regular version. But an envelope of the reduced-calorie cocoa mix contains a fourth less cocoa than the regular mix. At both Giant and Safeway, the prices for both products are the same.

Watch container sizes. Several "lite" products come in smaller container sizes than the original version.

A quick glance at a display of Marie's low-calorie salad dressings next to the company's regular dressings at an Alexandria Giant showed that they were each $2.29. But on closer examination, the coparison revealed that the low-calorie jars were 10 ounces, while thwe regular versions were 12 ounces.

In the case of fruit juices, you may not be even able to tell whether you're paying more for less. Late last month, the CSPI revealed the juice content on their product labels.

The group found that some products with more juice were cheaper than the ones with less juice. For example, Del Monte Pineapple Orange Fruit Blends, which does not disclose on the label that it consists of 50 percent juice, was selling at a Washington-area market for $1.60 a quart, while Johanna Farms Tree Ripe 100 percent Pineapple Orange Juice was selling for $1.43 a quart.

Bruce Silverglade, director of legislative affairs at CSPI, said that the difference may not have anything to do with the juice content, but simply that the smaller company (Johanna Farms) may have to undersell the more-recognized company (Del Monte) in order to compete.

Yet even between high-profile companies, there are inequalities. At an Alexandria Safeway last week, all of the varieties of Del Monte's Fruit Blends packaged in groups of three aseptic cartons were selling for $1.18. Comparable flavors of Minute Maid's fruit punches were also selling for $1.18. According to CSPI, however, Minute Maid's fruit punches haunches have only 10 percent juice, Del Monte's products have 50 percent juice.

The less-is-more argument of couse has another side. And that's what economists, manufacturers and retailers have to say about it.

According to the U.S. Department of Agriculture, an average of 30 percent of the retail cost of food is derived from the cost of the raw materials; the rest includes processing, packaging, transportation, wholesale and retail margins and advertising. That means a lot of factors that go into food prices have nothing to do with the food itself.

The "change in trucking rates may make more of a difference in a food cost than whether they (manufacturers) take the salt out," said Tom Earley, an agricultural economist with the Alexandria consulting firm of Abel, Daft and Earley.

If they do take the salt out, however, it may mean adding higher-cost seasonings. According to Doyle from Consumers Network, consumers are beginning to realize this from altering their own cooking habits and are becoming more tolerant when manufacturers charge higher prices for less salt.

Jim Moran, spokesman for the Campbell Soup Company, said that one of the reasons the salt is in there to begin with is that it is such a "low-cost flavor enhancer."

As is the case with reduced-sodium products, higher prices for less sugar may be the result of adding more of another, costlier ingredient. Pat Brailey, a spokesperson for Polaner's, said that while the company's "lite" preserves may have half the sugar of the company's regular product line, they contain more fruit. Fruit costs more than sugar.

Aspartame also costs more than sugar, which is one reason many aspartame-containing products -- such as puddings and gelatin -- are more expensive than the sugar-added ones.

Economist Earley said that in 1987, the wholesale price of aspartame was about 35 cents a pound, when adjusted to an equivalent amount of sweetening power as sugar. In comparison, the average price of all refined sugar offered for sale to manufacturers was more like 26 cents. High fructose corn sweeteners, which are used more often than any other kind of sugar or artificial sweetener, were selling for between 14 and 18 cents a pound.

Ingredients in a "lite" product may cost more simply because they are in short supply. Pat Farrell, spokesman for Van Camp Seafood, makers of chicken of the Sea Tuna, said that the company's dietetic product comes from a limited supply of albacore tuna which have less sodium in their meat. Chicken of the Sea Dietetic tuna, which was selling for nine cents more at a Giant last week than the Van Camp's regular white albacore, contains 30 milligrams of sodium per two-ounce serving of regular tuna. There is also no added salt in the dietetic version.

Separate production runs or more labor-intensive processing may also make a product more expensive. Doyle from Consumers Network said that consumers "don't complain so much anymore" about paying for decaffeinated proiducts, realizing an additional process is required.

According to odonna mathews, vice president of consumer affairs for Giant Food, the company's no salt-added bread is manufactured on a non-automated bread line where there is some hand-stacking involved.

Mathews speculated that specialized processing procedures may be one of the reasons why Kraft's lower fat cheese products sell for more than the company's regular cheese products at Giant. (They also cost more at Safeway.)

Scott Horne, a spokesman at Kraft's Chicago headquarters had another story. Horne said that in most market areas around the county, the products sell for the same price. The company generally sells the cheese products to retailers for the same price, although in some cases, there "could be a small variance," Horne added.

Horne speculated that stores may alter the pricing structure because the lower fat items are "perceived as value-added products. People are willing to pay a higher price" for them, he said.

Mathews of Giant Food said that the chain's sales of low fat and low salt cheeses are small. "Volume makes a big difference" in pricing, she emphasized.

In fact, volume, or supply and demand, may be one of the most crucial reasons why less costs more.

"The price is obviously going to be more for a product you sell less of," said Beth Adams of the H. J. Heinz company. "You pay a premium for its availability." Heinz's Lite Ketchup, which has half the calories and a third less salt than its regular ketchup, was selling for 10 cents more than regular Heinz ketchup at a local Giant last week. At an adjacent Safeway, Heinz's Lite Ketchup was also 89 cents, but was only seven cents more than Heinz's regular ketchup.

Liebman of CSPI believes that "you vote for salt reduction" when you buy products such as Campbell's low-sodium or Special Request soups, sales are good, then the prices should eventually go down, Liebman explained.

Indeed, many high-volume products that contain less don't cost more -- they cost the same. For example, at area chains last week, the same prices were charged for diet and regular salad dressings, six-packs of diet and regular sodas, light and regular beers, unsalted Hanover's pretzels and salted ones, unsalted Planter's peanuts and salted ones, Del Monte's and Giant's no-salt-added and regular canned vegetables, Hunt's no-salt-added and regular tomato sauce and Log Cabin's ""Lite" and regular syrups.

High volume is probably one factor in the price of milk, which is one of the rare products in which less actually costs less. Whole milk costs more than two percent which costs more than one percent which costs more than skim milk.

A more crucial reason for the declining price scale is this: While processors obviously ahve to pay to remove the fat from milk, they are able to use what they remove. The fat can be converted to other products such as ice cream, cheese, butter or half-and-half.

This logic doesn't seem to fit, however, when it comes to decaffeinating coffee. George Boecklin of the National Coffee Association said that coffee manufacturers are able to sell the caffeine they extract to soft drink companies or medicine manufacturers who then use it in their products. He said that he didn't know whether the money the coffee company makes from selling caffeine is enough to offset the costs of decaffeinating the coffee and then purifying the caffeine.