Potomac Electric Power Co. profits for the nine months ended Sept. 30 totaled $150.1 million ($2.95), up from $139 million ($2.69) for the corresponding 1984 period. Earnings per share were incorrectly reported in yesterday's Business section.

Potomac Electric Power Co. yesterday reported a 10 percent gain in earnings for the third quarter.

The utility said its net income was $79.7 million ($1.62 a share) on revenue of $429.5 million for the quarter ended Sept. 30, up from earnings of $72.5 million ($1.45) on revenue of $398 million for the comparable 1984 period.

For the nine months, profits totaled $150.1 million ($3.48), from $139 million ($3.18) for the corresponding 1984 period. Revenue for the nine months came to $1.025 billion, compared with $922 million for first three quarters of last year.

The company attributed the improvement to new customers, an increase in electricity sales and a traditionally higher consumption of electricity during the summer months. James Madison Ltd., the holding company for the Madison National Bank of Washington, said its earnings for the third quarter ended Sept. 30 came to $1 million ($1.23), up 71 percent from its $595,827 (72 cents) profit in the same quarter last year.

Earnings for the first nine months jumped 41 percent to $2.6 million ($3.18), from $1.9 million ($2.25) the year before. Total assets rose by 19 percent to $343.3 million, compared with $288.6 million on Sept. 30, 1984. Home Federal Savings Bank, based in Hagerstown, Md., said its net income for the third quarter ended Sept. 30 was $361,370 (91 cents), more than triple the $111,217 (28 cents) it earned in the 1984 quarter. The bank reported earnings of $877,228 ($2.20) for the nine-month period, also up sharply from $331,000 (83 cents) for the like period last year.

The bank's total assets increased to $147.4 million as of Sept. 30, compared with $138.3 million at the end of 1984. Planning Research Corp., the McLean professional services company, reported net income of $2.1 million (32 cents) on revenue of $104.8 million for the first quarter ended Sept. 30, compared with a $650,000 (10 cents) profit on revenue of $78.1 million in the year-earlier period.

The company attributed the gains, in part, to acquisitions completed after last year's first quarter. Entre Computer Centers, based in Vienna, reported net income of $8 million (85 cents) on revenue of $57.5 million for the fiscal year ended Aug. 31, up from a profits of $6.9 million (75 cents) on revenue of $29 million the year before.

For the fourth quarter, however, the computer retailer earned $934,000 (10 cents) on revenue of $18.2 million, down from a $2.2 million (24 cents) profit on revenue of $8.4 million for the 1984 quarter. Allegheny Beverage Corp., based in Cheverly, Md., said it earned $4 million (54 cents) on revenue of $304.4 million for the first quarter ended Sept. 28, a sharp improvement from the year-earlier period, when profits were $1.8 million (28 cents) on revenue of $116 million.

For the 26 weeks ended Sept. 30, the company reported net income of $63.2 million ($8.59) on revenue of $529.7 million, up from earnings of $3.8 million (59 cents) on revenue of $235.2 million in the comparable period the year before.

The company attributed the improvement to growth in the food service and vending division, as well as continued internal expansion.