Potomac Electric Power Co. yesterday reported its net income for the first four months of the year increased from $19.6 million to $21.8 million, and its earnings for common stock sharehlders climbed from $14.6 million (35 cents a share) to $16.4 million (38 cents).

Pepco's revenues increased from $221.9 million to $283.4 million for the first four months. For the last 12 months, revenues totaled $917.5 million, up from $745.7 million in the year ended in April 1980.

For the latest 12-month period Pepco posted net income of $106.3 million, up from $89.1 million and common stock earnings of $90.5 million ($2.12) up from $74.9 million ($1.81).

Virginia Electric and Power reported its net income for the month of April fell to $11 million (6 cents a share) from $14.8 million (11 cents) last year.

For the latest 12 months, Vepco earned $237.8 million ($1.85) compared with $206.4 million ($1.68) a year earlier as revenues increased to just over $2 billion from $1.9 billion.

Baltimore Gas & Electric Co. earned $53.7 million ($1.39 a share) for the first four months of the year, up from $40.5 million ($1.04), while its revenues climbed to $490.2 million from $408.6 million. The 12-month period produced income of $152.7 million ($3.99) from $117.2 million ($3.04).