Dart Group Corp. yesterday reported that net income for the year ending Jan. 31 fell to $9.9 million ($5.28 a share) from $82.3 million ($45.15) for the same period the previous year.

The previous year included a gain on the sale of Dart's drugstore division of approximately $75 million.

The company reported sales of $97.8 million for the year ending Jan. 31 compared with $73.8 million for the previous year.

In the fourth quarter, Dart Group had a net income of $136,000 (7 cents) on sales of $26.4 million compared with $2.9 million on sales of $20.7 million during the same period in the previous year.

*Potomac Electric Power Co. reported first-quarter earnings of $40.7 million (79 cents a share), up 17 percent from profits of $34.8 million (66 cents) in the same period of last year.

First-quarter revenue increased to $324.6 million from $290 million.

Pepco said expanded electric-heating sales and a strong local economy contributed to the increase in sales. The company, based in the District, noted that its earnings have improved while customer prices have remained stable.

*Norfolk Southern Corp., citing reduced fuel and labor costs for its railroad subsidiaries, on Tuesday reported a 3.9 percent profit gain in the first three months of 1986 from a year earlier.

Norfolk Southern said its after-tax earnings of $103.7 million ($1.65 a share) in the first quarter were up from $99.8 million ($1.59) in the same period of 1985.

"During the first quarter, we continued to reap the cumulative benefits of our 1982 consolidation," company Chairman Robert B. Claytor said in releasing the results. "Tight cost control and reduced fuel expense offset a slight decrease in railway operating revenues and produced the best first quarter since our consolidation."