Riggs National Bank and Maryland National Corp. respectively the largest commercial banking firms in the District and Maryland, yesterday reported significant increases in profits for the second quarter and six months ended June 30.

First half earnings from operations at Riggs and its wholly-owned subsidiary, Central Charge Service, rose 19 per cent to $6.7 million ($2.25 a share) compared with $5.6 million ($1.89) in the same 1976 period. Net income, including gains or losses from securities transactions, was basically the same in both periods.

In the second-quarter alone, Riggs earned $3.5 million ($1.17) compared with $2.9 million (99 cents), an increase of nearly 19 per cent.

Riggs chairman Vincent C. Burke Jr. attributed the 1977 increase to a higher volume of loans and investments, including more tax exempt securities. While non-interest income increases, the gain was more that offset by higher operating expenses, Burke said.

Deposits totaled $1.6 billion on June 30, a record high, compared with $1.4 billion a year earlier. Loan volume was up 20 per cent to $867 million and total resources increased 13 per cent to $1.84 billion.

The bank company earned a 10.3 per cent rate of return on stockholders' equity in the first six months of 1977 compared with 9.1 per cent in the same period of last year.

Maryland National Corp., holding company for Maryland National Bank, reported first half operating profits of $8.7 million ($1.22 a share), up 33.5 per cent from $6.5 million (91 cents) in the 1976 period. Net income was $1.22 a share vs. 92 cents.

Chairman Robert D. H. Harvey said the gain was due primarily to a sharp improvement in second-quarter profits - to $4.4 million (61 cents vs. $1.9 million (26 cents), both before and after accounting for securities transactions.

Marynat benefited in the recent quarter from a lower reserve for possible loan losses of $2.2 million compared with $6.1 in the 1976 period. But one-third of the increase in the first half reflected loan and deposit growth and higher interest income, Harvey said.

Average deposits in the 1977 period were $2.05 billion compared with $1.94 billion a year earlier while loan volume increased $1.7 billion from $1.5 billion.

National Savings & Trust Co., the fourth-largest D.C. bank, reported first-half profits of $1.4 million ($3.11 a share), up 37.6 per cent from $1 million ($2.26) in the 1976 period. Total deposits declined to $316 million from $326 million. Directors voted a regular quarterly dividend of 54 cents a share.