Benefitting from higher interest-rate income and margins as well as modest loan volume expansion, Virginia National Bankshares Inc. and First American Bank of Maryland yesterday reported higher profits from operations in 1979.

Virginia National, based in Norfolk, said earnings before securities transactions totaled $21.3 million ($3.13 a share) last year compared with $18.8 million ($2.78). Fourth-quarter operating earnings fell to $5.6 million (83 cents) from $6 million (89 cents), as government credit-tightening measures affected some banking profit margins.

First American, a Silver Spring-based institution controlled by the Financial General Bankshares, holding company of Washington, said operating profits for the year rose to $2.48 million ($2.53 a share) from $2.2 million ($2.21). Fourth-quarter earnings increased to $670,000 (69 cents) from $571,000 (57 cents).

Chairman C. A. Cutchins III, of Virginia National, said his holding company's record earnings were "particularly gratifying considering the fact that a general, economic slowdown made comparative earnings growth difficult to sustain in the latter part of the year." The Norfolk firm's main subsidiary is Virginia National Bank, the largest statewide bank.

Profitability as measured by return on assets, rose to .87 percent in 1978. The return on shareholders' equity rose to 15.7 percent from 15.51 percent. Total assets increased 4 percent to $2.5 billion.

First American of Maryland's president, G.J. (Bud) Manderfield, attributed, his bank's record performance to an increase in yields on interest-earning assets and higher interest income resulting from "a conscientious effort to control growth in both loans and deposits."

Loan volume rose 3 percent to $167 million while deposits grew by 6 1/2 percent to $265 million. Assets were up 9 percent to $300 million The return on average assets rose to .90 percent from .86 percent and return on stockholders equity was 12.49 percent vs. 12.1 percent.