The supermarket price war that slashed the profits of Giant Food Inc. lst spring will force the supermarket chain into the red for the summer, Giant disclosed yesterday.

Giant officers said they "anticipated a loss" for the quarter ending Aug. 14, and that it will be Giant's first quarterly deficit in at least 10 years.

Giant spokesman would not project how much money the chain expects to lose this summer but said, "pofits are not expected until the later part of 1981."

The loss is the result of a price war Giant started in April, when it announced it was no longer marking prices on individual items and was starting a "warehouse pricing" policy that would cut the costs of hundreds of items.

The four-month food fight continued to push down Washington food prices last month, but not as much as the two months before, the Labor Department reported yesterday.

Local food prices dropped 0.4 percent in June, compared with 2.4 percent in May and 2.7 percent in April, the Labor Department said.

Giant's announcement indicated the chain has no intention of backing away from the price war at present. The company said it "continues to be encouraged by the sales gains" it is getting but has still not won as much new business as it had hoped.

The labor savings expected to result from ending item price marking have not yet been achieved, the company said, indicating that Giant's earnings are being hurt by high labor costs. Giant's labor contracts prohibit the chain from laying off workers because of the decision to stop marking prices.

Vice President David B. Sykes said Giant hopes to be able to absorb the people who formerly marked prices in other jobs by the end of the year. He said normal turnover of employes, which had been expected to create some vacancies, has slowed because of the decision of Pantry Price supermarkets to close its Washington-Baltimore stores and lay off hundreds of employes.

Giant is considering bidding on some of the Pantry Pride locations, the company's announcement said, but Giant officials specifically denied reports they may try to buy as many as 50 former Pantry Pride outlets.

Giant's projection that it will show its first quarterly loss came just a few days after the company was proclaimed "the best-managed chain" by Chain Store Age Supermarkets, the leading industry publication.

The magazine noted that Giant's warehouse-pricing decision "took the competition by surprise and the market by storm -- just as Giant has planned."

Washington-area consumers are benefiting from the price war with continuing declines in food prices, yesterday's consumer price index showed.

The declines, totaling 5 1/2 percent, reversed an uptrend in food costs. Grocery store prices had gone up one-half percent in February and March, after increasing 1 1/2 percent in December and January.

The slower drop in prices indicates the price cutting in the supermarket war is almost over, said Labor Department economists Floyd Rabil.

"Warehouse pricing has become the trend in Washington," Rabil said. "It looks like this has pretty well been absorbed in the market now. They've cut prices as low as they can go. They've reached a plateau."

Prices for cola drinks, fish and seafood, pork, most canned and frozen foods, most dairy products, sugar and coffee, the Labor Department said. But those prices were partially offset by price increases for fresh fruits and vegetables, beef, poultry and bread.

Fruit and vegetable prices are expected to decline when harvesting of the country's summer crops begins next month, Rabil said.

Beef and poultry prices rose as part of the national trend, Rabil said. Many farmers are slaughtering their hogs because of low pork prices caused by an abundance of pork last year, Rabil said. Beef farmers "aren't expanding herds as much as they should," Rabil said.

The price of bread also rose, Rabil said.

During June, prices of cereal and bakery products rose 0.4 percent while meats, poultry, fish and eggs dropped 1.1 percent and dairy products dropped 2.6 percent. Fruit and vegetable prices, however, rose 6.4 percent and other food items cost 3 percent more.