Virginia Electric & Power Co., in a preliminary report on 1978 operations, said yesterday that overall profits increased slightly but that because more shares of common stock are outstanding, per-share earnings for the year declined by 4 cents.

Chairman T. Justin Moore Jr. said Vepco earned $204.3 million ($1.88 a share) in 1978 compared with $189.8 million ($1.92) the previous year. Revenues rose to $1.46 billion from $1.37 billion.

In the final three months of the year, the Richmond-based utility earned $45.8 million (39 cents a share) compared with $45.5 million (43 cents) in the 1977 period. Revenues rose to $339 million from $329 million.

In 1978, Vepco had an average of 80 million common shares owned by investors compared with 74 million in 1977, which accounts for the dilution in per-share figures despite the slight overall gain.

Moore said the lower earnings per share resulted from "delays" in granting requests for higher electricity rates. The additional stock had to be sold, he added, to help finance nuclear and pumped-storage construction programs.

Vepco's three nuclear generating plants provided more than 35 percent of the company's output for the year. Vepco services the most populous regions of Virginia, including most of the Washington suburbs.

Macke Co., a food service and vending firm, reported record first-quarter earnings yesterday. In the three months ended Dec. 31, the Cheverly company earned $1.37 million (45 cents a share), up 20 percent from $1.15 million (38 cents) a year earlier. Sales jumped 19 percent to $63 million.

Chairman Meyer Gelfand said a strong national economy was a major contributor to the record sales and profit growth.