Riggs National Corp., parent of Riggs National Bank, reported a net loss of $11.8 million (85 cents per share) for the second quarter, after adding $32 million to its loan loss reserve because of expected losses from sour Third World loans.

The second-quarter figures represent a sharp drop from the same period a year ago, when the bank holding firm showed net income of 9 million (65 cents).

For the first six months of the year, Riggs reported a net loss of $1.6 million (11 cents), compared with net income of $21.4 million ($1.66) a year ago.

The company said net interest income dropped slightly in the first six months of 1986 from $75 million to $71.8 million. The bank attributed the decline in part to lower interest rates and the placing of $37 million worth of loans on nonaccrual status because of Brazil's interest moratorium.

Sovran Financial Corp. of Norfolk reported that earnings rose 8.9 percent in the second quarter, from $36.9 million (85 cents per share) to $40.1 million (94 cents). For the first six months of 1987, net income totaled $78.6 million ($1.85) up 10.4 percent over the $71.2 million ($1.67).

The bank holding company said the earnings increase was the result of higher volumes of earning assets and gains on the sale of mortgage-servicing rights and certain other assets. The growth in income was partially offset by noninterest expenses, which grew 3.6 percent in the second quarter, the company said.

The Federal National Mortgage Association reported net income of $62 million (75 cents) in its second quarter, up 31.6 percent from $47.1 million (63 cents) in the 1986 second quarter. For the first six months of the year, Fannie Mae's net income was $118.4 million ($1.47), up 45 percent from $81.8 million ($1.10) from the same period a year ago.

The company, which makes a secondary market in home mortgages, enjoyed strong growth in the mortgage-backed securities business, offsetting declines in commitment fees in the quarter, Fannie Mae said.

Strategic Planning Associates, a Washington-based international management consulting firm, reported that net income rose 79 percent and revenue was up 55 percent in its third quarter ended May 31.

The company said net income in the quarter totaled $1.2 million (30 cents), compared with 652,000 (19 cents) in the same period a year ago. Revenue totaled $11.2 million, up from $7.2 million in the 1986 third quarter, the company said.

AVEMCO Corp., a Frederick-based insurance company, reported net earnings of $4.9 million (51 cents) in its second quarter ended June 30, up 67 percent from $2.9 million (32 cents) reported in the same period a year ago. For the first six months of the year, AVEMCO reported profits of $10 million ($1.04 per share), compared with $5.3 million (57 cents per share) in the first six months of 1986.