Giant Food Inc. appears to be winning the price war it launched one month ago.

Retail analysts here estimate Giant's sales have increased about 15 percent since April 5 when the chain unveiled a dramatic new program offering customers lower prices on selected items -- a savings made possible by the elimination of the practice of marking a price on each item in the supermarket. e

Other major chains, including Safeway and A&P, "have barely held their own or have gone down slightly," the analysts said, despite efforts by those chains to match the Giant price cuts and continue stamping prices on most items.

"One exception would be the warehouse operation, such as Basics, which are going very strong," said Jeffrey W. Metzger, executive vice president of Food World, a trade publication that does market-share studies of supermarkets and then publishes the results. Food World generally is regarded as one of the best sources of accurate information on this subject.

Metzger said the estimated 15 percent increase in Giant sales was based on Food World surveys of customer traffic in supermarkets and interviews with vendors who monitor retail store sales.

"We have a pretty good fix on what a store does each week," Metzger said.

Giant officials siad that sales volume had increased but would not say how much. "We don't give out those figures," said Barry Scher, a company representative.

Other chains denied that their sales have fallen.

Ernest G. Moore, a Safeway spokesman, said that sales actually had increased during the past month. He said the increase represented two trends: "People are buying more to take advantage of our low prices . . . and maybe we are taking some business away from our competitors."

Grand Union said its sales were about the same -- "which means we are retaining our market share, which is the name of the game," according to Don Vaillancourt, a chain vice president. Moreover, he said that Giant had not encroached at all on the volume at the Grand Union Basics warehouse stores in the Washington area.

In its program, Giant reduced prices on 1,500 to 2,000 items -- roughly 17 percent of the merchandise in an average supermarket. Among the foods that the chain marked down were such basics as milk, down from $2.09 to $1.81 for a gallon of the Giant brand; Starkist tuna, down from $1.19 to 77 cents for a 6 1/2-ounce can, and Kraft Velveeta cheese, down from $4,39 to $3.23 for a two-pound box.

The company has declined to say how much money it saves by the elimination of item-pricing. But Terry Gans, director of corporate operations for Giant stores, said that an average supermarket employs about 80 people. In the past, two to three of those employes would have had to work full time to mark prices on individual items in the store. Now, those employes are free for other duties, such as keeping shelves fully stocked. This reassignment of labor enables the store to operate more efficiently, Gans said.

Giant net earnings for its past fiscal year totaled $18.3 million; sales fell just short of $1.5 billion. That works out to a profit of $2,742 per week per store for Giant and sales of $222,143 per week per store. The chain earnings represented 1.23 percent of sales for the year.

If the company can avoid marking prices on individual items, the savings could increase its profits. But the final figures on that won't be known until June when the chain publishes its quarterly report.

The pricing program initiated last month by Giant caught its customers and its competitors by surprise.

A coalition of consumer groups applauded the price-cutting but criticized the policyof not putting prices on individual items in the stores. The coalition called a press conference, picketed for three hours outside one Giant store and urged shoppers to consider switching to supermarkets that still price their products individually.

Giant was able to outmaneuver the critics -- at least for the moment -- by focusing on the savings that the new system of shelf-pricing can bring customers. The conflict between the company and the consumer coalition may resurface, however, if the consumers continue their crusade for laws requiring a price on every product.

Charlotte Newton, chairman of the coalition for item-pricing, said the group also will conduct a survey soon to determine if Giant has kept the low warehouse prices that were advertised at the beginning of the price war.

Other consumer advocates,including Carol Foreman, former assistant secretary in the U.S Department of Agriculture, lament the loss of a "very important piece of consumer information" -- the individual item price.

Foreman also said that other supermarkets that copy the Giant lead in adopting shelf-pricing may not be as efficient or as accurate as Giant.

Industry interest in the Giant maneuver has been at least as intense as that of the consumers.

"Everybody has been dying to do this [elimination of item-pricing]," said Bill Saporito, assistant editor of Chain Store Age Supermarkets, a trade publication. "But until now no chain has succeeded in doing it in every store and getting away with it. Is Giant getting away with it? The reaction from consumers hasn't been that bad. And you know that if there had been any drop in volume, they would have dropped the program."

At present, Giant is the only chain in the Washington region with the equipment necessary to switch completely to the new pricing system. All 126 of its stores have electronic scanners that can read product codes -- the lines and bars that appear on most packages in a store -- and automatically record the price.

Safeway has scanners in 12 of its 125 stores. In addition, 35 of the Safeway stores have electronic registers that allow the cashier to punch in a special code representing a product. The register then rings up the price automatically on the register. Electronic registers are capable of handling about 300 codes.

All 51 A&P supermarkets here have either electronic registers or automatic scanners.

None of the 48 Grand Union stores has computerized checkout facilities.

Although a number of other supermarkets around the nation now have shelf-pricing rather than item-pricing, Giant is believed to be the only supermarket chain with the shelf-pricing system in use in all of its stores.

The program was tried by the Publix chain, which has 251 stores in Florida, but dropped after six months because of negative public reaction.

"We listened to our customers and our customers, who had been so confused by the press and the politicians, were not yet ready to accept this new technology," said Mark Hollis, a vice president of the company, which is as highly regarded in Florida as Giant is in the Washington area.

Hollis said the the chain had anticipated a savings of a much as $800 per week per store once the program was established.

But hopes for those savings dwindled as local jurisdictions in Florida passed ordinances mandating item-pricing. Finally, in January 1981, Publix began putting prices back on individual items again.

There were some important differences in the approach the Publix and Giant took in their programs.

Publix eliminated individual prices gradually, over a period of several months. Finally, in September 1980, the chain dropped item-pricing almost completely. But there was no announcement of the change and no reduced price program.

By contrast, Giant took out special advertisements heralding its new lower warehouse prices and telling customers that the savings were possible due to greater efficiencies such as the shelf-pricing concept.

Now, after one month, industry analysts agree that Giant is ahead.

Metzger, the Food World editor, said that the increased sales volume at Giant supermarkets during April has had the effect of increasing the chain's market share from about 33 percent in the past to perhaps 33 1/2 percent to 34 percent. That compares to Safeway's 27 percent.

"While the figures aren't complete, indications are the Giant has again increased its share of the market over the past 12 months while its competitors have remained flat," Metzger said.

But it is too early, Metzger said, to know if the increased sales volume will help Giant profits. "Sales are often related to profit, but because Giant took such a radical approach with this program, there is no way to know the effect on profits at this time," said Metzger.

Metzger predicts, however, that if Giant is happy with its profits, shelf-pricing is here to stay.