Following a stream of troubling news about the local economy, two Washington area retailing mainstays, Giant Food Inc. and Hechinger Co., yesterday reported solid increases in sales and earnings for the second quarter.

Profits at Landover-based Giant, the 150-store supermarket chain that dominates the retail food industry here, jumped 16.3 percent to $25.8 million (43 cents a share) for the second quarter ended Aug. 11, from $22.2 million (37 cents) in the same period last year.

Revenue was up 4.3 percent for the second quarter to $764 million from $732.8 million a year ago. Giant blamed its slower than normal sales growth in the second quarter on sluggishness in the local economy.

For the first six months of the year, profits rose 11.4 percent to $54.3 million (91 cents) from $48.7 million (81 cents) for the same period last year. Sales rose 5.2 percent to $1.53 billion from $1.46 billion in last year's first half.

At Hechinger, earnings in 1990 continued to rise following three straight quarters of declining earnings last year.

Profits for the Landover-based hardware and housewares retailer were up 10.3 percent in the second quarter ended Aug. 4, to $10.8 million (30 cents) from $9.8 million (27 cents) a year ago.

Sales for the second quarter increased 15.6 percent, to $389.7 million from $336.9 million last year.

Net income for the first half of 1990 rose 12.3 percent to $19.2 million (53 cents) from $17.1 million (48 cents), while revenue rose 20 percent to $734.3 million from $611.7 million.

Comparable store sales at Hechinger were flat for the second quarter and up 4 percent for the first half of the current fiscal year. Hechinger operates 87 Hechinger stores, 20 Home Quarters Warehouse stores and six Triangle Building Centers in 14 states and the District.

Both Giant and Hechinger appeared bullish about the future, announcing new store openings.

Giant will open a store in the Adams Square Shopping Center in Arlington today and plans to open another in the Village Center at Sully Station in Centreville, Va., in November.

Hechinger opened two Home Quarters Warehouse stores in the South in the second quarter and opened two more in the Boston area in mid-August. Hechinger has at least 15 such stores planned for the New England region over the next two years.