Virginia Electric and Power Co.'s profits fell by $3.8 million last year to $237.8 million despite a $42 million increase in revenues to $2.16 billion.

Vepco President William W. Berry blamed the drop in earnings on high interest rates, mild weather that reduced electricity consumption, the sagging economy and "the short-term negative impact" of efforts to boost long-term profits.

The decision to cancel construction of a nuclear power plant, heavy spending to convert oil-burning generators to coal and investments in upgrading the efficiency of coal-fired plants eventually will aid earnings, but they hurt in the short run, Berry said.

Though total revenues climbed 2 percent, overall profits were down 1.6 percent, and earnings per share of common stock dropped 8.3 percent, or 16 cents, to $1.77 a share from $1.93. The decline in per-share profits was greater than the drop in net income because Vepco issued about 6.3 million shares of new stock during the year.

For the fourth quarter of 1981, Vepco's net fell to $67.1 million (50.6 cents) from $73.7 million (58.7 cents), and revenues slipped to $555 million from $560.6 million.

Equitable Bancorporation of Baltimore boosted its 1981 earnings to $9.96 million ($2.40 a share) from $9.36 million ($2.25) the previous year. Assets of the bank holding company climbed to $2.08 billion from $2.02 billion.

For the fourth quarter, profits fell to $1.56 million (35 cents) from $2.8 million (70 cents) for Equitable, which owns Equitable Trust Co. of Baltimore, Columbia Bank and Trust Co. of Columbia, and Farmers & Merchants Bank of Hagerstown.

Syscon Corp., a Washington computer software firm, reported annual income of $2.4 million ($1.05 a share) on revenues of $61.1 million for 1981, up from $1.8 million (80 cents) on revenues of $52.3 million the prior year.

Fourth-quarter earnings of Syscon climbed to $761,000 (33 cents) from $550,000 (24 cents), while revenues increased to $15.8 million from $14 million.