Giant Food Inc., the area's largest food retailer, reported that profits more than doubled in the 52 weeks ended Feb. 26 to $37.2 million ($2.53 a share) from $16.8 million ($1.14) in the 52 weeks ended Feb. 27, 1982.

During the same period, sales rose 10 percent from $1.68 billion to $1.85 billion, the Landover-based firm reported.

CSX Corp., the big railroad, said a 20 percent decline in coal traffic hit first-quarter profits hard. They declined to $35.6 million (84 cents a share) from $48.2 million ($1.16) during the first three months of 1982. CSX said revenue fell from $1.29 billion to $1.13 billion.

In a statement, Giant Food said that the sharp increase in earnings was the result of stringent efforts by the company to control or reduce costs.

Giant's earnings in the period ended Feb. 26 were 2.01 percent of sales, up sharply from the 1 percent it earned in the earlier 52-week period. At most supermarkets, profits are about 1 percent of sales.

But Margaret Gilliam, vice president at the investment banking company First Boston Corp., said Giant should be expected to earn more than the standard food chain because the company is a major seller of nonfood items as well, especially drug store products. Pharmacy items generally have a higher margin of profit than do most foodstuffs.

Gilliam said that Giant is a well-run company, but that other chains with a mix similar to Giant's--such as Dillon Co. in Kansas--report a comparable level of profits. Of the 130 stores in the Giant chain, 70 are combination food and drug stores and a few are stand-alone pharmacies.

For the past 15 months, Giant has earned about 2 cents on every dollar of sales.

In the spring of 1981, Giant launched a major price-cutting campaign that evolved into a price war with its major area competitor, Safeway Stores Inc., which is based in Oakland, Calif. As a result of that price war, which has long since ended, Giant reported a loss for the first half of the year. But profits soon recovered when the price-cutting stopped.

Giant said that, besides its cost-cutting program--especially an emphasis upon keeping inventory levels lower than before--its manufacturing plants contributed to higher earnings as did the higher volume of sales.

CSX--which resulted from the merger of the Chessie system and the Family Lines two years ago--said that general commodity traffic was down 2 percent from the year before and said other traffic such as intermodal--which combines rail and truck shipping--and automotive were up strongly.

CSX said the relatively small decline in general commodity shipping reflects the ending of the recession and returning strength in the industrial sector.

But coal is the single most important commodity that CSX hauls. A mild winter and the worldwide recession sharply reduced demand for the fuel, the company said.