Seven companies based in Maryland, Virginia and the District are included in May Fortune magazine listing of the country's 500 top industrial corporations.

Fortune reported in its annual survey that, in general, the top companies made a vigorous comeback last year from a mediocre 1975. Combined sales of the "Fortune 500" totaled $971.1 billion compared with $865.2 billion in 1975, while profits rose to $49.4 billion, a gain of more than $30 billion.

Exxon Corp., the world's largest petroleum firm, again was No. 1 on the list, which is ranked by sales volume. But a comeback for the larger auto manufacturers last year helped General Motors Corp. to narrow the gap between itself and Exxon and actually to surpass Exxon in terms of total profits.

Ford Motor Co. overtook Texaco, Inc., for third place with annual sales of $28.8 billion compared with $26.45 billion for Texaco now fourth.

Companies based in Maryland, Virginia and the District on the 1976 list are as follows:

Reynolds Metals Co., Richmond, 108 (up from 123 the previous year), sales of $2.08 billion; the alumunum manufacturer ranked 62d in total assets ($2.34 bilion) and 50th in total return to investors in 1976 (85.78 per cent), a formula that takes into account appreciation in stock price over the year plus dividend payments.

Martin Marietta Corp., Bethesda, 189 (up from 193), sales of $1.2 billion; the diversified aerospace and construction materials company was 99th in total return to investors (66.91 per cent).

Ethyl Corp., Richmond, 194 (up from 195), sales of $1.15 billion.

Black & Decker Manufacturing Co., Towson, 276 (up from 284), sales of $748 million.

Universal Leaf Tobacco Co., Richmond, 290 (down from 260), sales of $706 million; the tobacco company was 84th in total return to investors (71.67 per cent).

Crown Central Petroleum Co., Baltimore, 365 (down from 356), sales of $512 million; total return to investors ranked Crown Central at 17 (119.33 per cent).

Washington Post Co., the District, 452 (up from 486), sales of $376 million; the communications firm was ranked 10th among the 500 firms in total return to investors last year (134.88 per cent), reflecting a sharp runup in Post Co. stock.