The Potomac Electric Power Co. yesterday reported a 23.3 percent increase in net income during 1980 to $104.1 million, from $84.4 million in 1979. Earnings per share amounted to $2.10 compared with $1.73 in 1979.

Officials attributed the gain to higher prices and sales volume and intensified cost control. W. Reid Thompson, Pepco's chairman, said earnings still were "well below" those needed to attract investors.

In a separate report, Radiation Systems Inc. announced its earnings for the second half of 1980 were up 15.2 percent over the last six months of the previous year to $370,000, from $329,000 in the July-to-December period of 1979.

At the same time, George Mason Bank in Fairfax announced its 1980 earnings more than doubled last year, soaring to $254,684 from $121,578 in 1979. Earnings per share amounted to $2.72 compared with $1.30 in 1979.

And American Realty Trust of Arlington reported net income of $1.46 million for the fiscal year that ended last Sept. 30, following a $365,321 net loss in the previous 12-month period.

Radiation Systems attributed its gains primarily to increased sales of commercial satellite antenna products. Earnings per share totaled 48 cents in 1980, up from 41 cents the previous year.

American Realty Trust credited increased earnings and revenues from its hotel and motel operations and rental and lending activities.

Pepco's 1980 figures were accompanied by a report showing net income for the last three months of the year at $20.6 million, up $1.02 million, or 5.2 percent, from the final quarter of 1979.