Maryland National Corp., the Baltimore-based holding company for Maryland National Bank, reported essentially flat earnings for its first quarter ended March 3.

The corporation's net income for the quarter totaled $10.3 million ($1.31 a share) compared with $10.3 million ($1.36) in the comparable period last year.

Income before securities transactions in the first quarter was $10.7 million ($1.36) compared with $10.6 million ($1.39) in the first quarter of 1981.

Maryland National said mandatory redemption of certain Penn Central securities in 1981 resulted in a 19-cent-a-share increase in first-quarter earnings. In this year's first quarter, a previously announced exchange of $5.7 million debt for equity resulted in an increase of 15 cents a share.

Maryland National opened a subsidiary bank, Maryland National N.A., in Delaware last month to handle its credit card accounts. The Delaware credit card operation "was unprofitable in the first quarter," but will "add substantially to bottom-line results" in the remaining quarters, said Maryland National Chairman Robert D.H. Harvey.

In early March, Maryland National also announced a public offering of $50 million of 15 1/2 percent notes due March 1, 1987. The proceeds have been used to fund the newly formed credit card subsidiary.

At the end of the first quarter, Maryland National, parent of the state's largest bank, reported total assets of $4.3 billion, $2.7 billion in deposits and $2.5 billion in loans.

Virginia National Bankshares Inc. of Norfolk said net income for the first quarter increased 5.1 percent, from $6.8 million (97 cents) to $7.2 million (98 cents), a record for the period.

Income before securities transactions for this year's first quarter was $7.3 million ($1.01) compared with $7.2 million or ($1.01) for the comparable period a year ago.

Virginia National had assets of $3.1 billion on March 31, up 19.1 percent from a year earlier.

NS&T Bank's 1981 net income before securities transactions increased by $5.35 million, or 13.1 percent. President Joseph H. Riley told stockholders at the annual meeting that the bank had the highest earnings in its 114-year history. Net income per share was $3.52; the dividend paid was $1.77. Return on equity amounted to a record 14.6 percent. Total deposits last year increased by $80 million to $485.9 million.

Avemco Corp., a Bethesda-based company involved in aviation-related insurance and financial services, reported record first-quarter earnings yesterday of $1.34 million (54 cents a share) compared with $1.14 million (46 cents) in 1981, which was the previous record.

First-quarter revenues grew 23 percent to $8.5 million from $6.9 million in the comparable period of 1981.

Chairman Arnold H. Johnson attributed the favorable results to investment earnings and to the record first-quarter premiums written by Avemco Insurance, $10 million worth, an increase of 18 percent.