While other major airlines were counting their pennies, Washington-based USAir Inc. yesterday reported a second-quarter operating profit of $39.98 million--the highest quarterly pretax earnings in the company's 43-year history.

Among other local companies reporting are four banking companies--Equitable, First Maryland, Dominion and First Virginia--Media General, Dan River and Preston Trucking.

The airline's pretax profits were 35.7 percent higher than the $29.47 million last year. But USAir's net earnings fell 20.4 percent to $20 million for the second quarter from $25.15 million in the year-earlier quarter. Earnings per share were $1.15, compared with $1.58 last year, when fewer shares were outstanding.

Revenues increased to $335.4 million from $296 million in the second quarter; in the half, revenues grew to $614.6 million from $548 million.

Equitable Bancorporation of Baltimore reported second-quarter earnings before securities transactions increased to $2.94 million (86 cents a share) from $2.325 million (53 cents) last year.

Equitable's net income dropped 8 percent to $2.38 million (70 cents) for second quarter from $2.59 million (59 cents) a year earlier.

For the half, income before securities transactions was $5.64 million ($1.53) compared with $5.26 million ($1.21) for 1981.

First Maryland Bancorporation of Baltimore posted income before securities transactions rose to $6.34 million ($1.18) for the second quarter from $6 million ($1.17) for the same period a year ago.

Securities losses of $177,000 in the second quarter put net income at $6.16 million ($1.14), compared with net earnings of $5.94 million ($1.15) last year. Net income for the first half was $11.62 million ($2.16) compared with $11.53 million ($2.24) in 1981.

Dominion Bankshares Corp. of Roanoke had income before securities losses of $6.02 million (61 cents) for the second quarter, compared with $5.82 million (59 cents) last year. Thumping securities losses of $1.12 million in the second quarter left a net income of $4.90 million (50 cents), compared with a net of $5.57 million (57 cents) in the same quarter last year, when the company lost $253,000 in securities transactions.

Dominion finished the half with a net income of $9.44 million (96 cents), down from a net income of $11.43 million ($1.17) a year earlier.

First Virginia Banks Inc. of Falls Church yesterday reported record earnings for the second quarter and the first half of 1982.

Second-quarter earnings before securities transactions were $6.48 million (52 cents), compared with $5.05 million (40 cents) last year. Net income for the second quarter was $6.45 million (52 cents). Net income of $5.05 million (40 cents) in the second quarter of 1981 virtually matched income before securities transactions for the same period.

First Virginia's operating profits for the half were $11.93 million (95 cents), up 22 percent from $9.73 million (78 cents) earned in the first half of 1981.

First Virginia's net income for the first half of 1982 was $11.88 million (95 cents), up from $9.74 million (78 cents) for the same period last year.

The company said the increase in earnings for the six months ending last June 30 "was the result of a 10 percent growth in average earning assets and a higher level of interest rates."

Media General Inc. of Richmond also announced record earnings. The company said revenues were $99.61 million for the second quarter, compared with $93.2 million for the same period last year. Net income was $9.07 million ($1.28), compared with $8.7 million ($1.22) in the second quarter of 1982.

Revenues for the half were $196.5 million, up from $178.9 million last year. Net income for the latest half-year period was $16.2 million ($2.29), up from $15.1 million ($2.10) last year.