Third-quarter profits at Atlantic Research Corp. rose 43 percent over the previous year, boosting earnings to $5.6 million (60 cents a share) from $3.7 million (42 cents).

Atlantic Research, based in Alexandria, develops solid propellant rocket motors and gas generators for aerospace and defense projects.

The company's sales for the quarter totaled $103.5 million, up 13 percent from $91.8 million in revenue for the same quarter in 1986.

Atlantic Research's earnings for the first nine months of this year were $14.3 million ($1.55 a share) on sales of $300.5 million. That compares with a net income of $12.7 million ($1.41) on sales of $269.3 million for the same period in 1986.

Riggs National Corp. reported that profits were down 6.4 percent for the third quarter, falling to $7.1 million (51 cents) from $7.6 million (54 cents) in the same quarter last year.

Riggs' net income for the first nine months of 1987 was $5.5 million (39 cents), a 81 percent decline from the $28.9 million ($2.18) earned in the same period last year.

Officials attributed the decline in earnings to the addition of $32 million to Riggs' loan loss reserve and to an increase in nonaccrual loans.

Riggs National Corp. is a multibank holding company with banks in the District, Virginia and the United Kingdom. The company is based in the District.

Sovran Financial Corp.'s profits were up 15.6 percent for the quarter, rising to $43.1 million ($1.01) from $37.3 million (88 cents) in the year-ago period.

Sovran's net income for the first nine months was $121.7 million ($2.86), up 12.2 percent from the $108.5 million ($2.55) earned in the same period in 1986.

Sovran Financial Corp. is the holding company of Sovran Bank N.A., Sovran Bank/Maryland, Sovran Bank/DC National and Sovran Bank/Del.

The company operates 358 banking offices in Virginia, Maryland, the District and Delaware; and it has an office in Nassau, Bahamas.

Quarterly earnings also were up at Second National Federal Savings Bank, of Salisbury, Md. Net income for the period increased 13.2 percent to $2.3 million (32 cents) from $2 million (34 cents) last year. The per share figure was affected by the sale of 1.1 million new shares of common stock in November 1986, Second National officials said.

The Salisbury bank reported record earnings for the first nine months of the year, up 17.1 percent to $6.9 million (97 cents) from a net income of $5.9 million (99 cents) in the year-ago period.

ERC International of Fairfax reported profits of $1.3 million (31 cents) on revenue of $32.0 million for the third quarter ending Sept. 30, compared with profits of $368,000 (9 cents) on revenue of $26.4 million during the same period last year.

For the nine months, ERCI reported profits of $3.9 million (91 cents) on revenue of $89.3 million, compared with profits of $1.7 million (40 cents) on revenue of $71.7 million in the same period last year.

ERCI provides professional support services for a wide variety of government and commercial clients, including those involved in defense, energy and environmental programs.

CFS Financial Corp. of Fairfax reported that net income for the first quarter ending Sept. 30 fell to $16,000 (0.5 cent) from $1.3 million (42 cents) in the same period last year.

CFS officials said the decline was caused mostly by losses from the operation of its jointly owned mortgage banking company, First Southern Mortgage Corp. CFS Financial is the holding company for Continental Federal Savings Bank, which operates 25 full-service banking offices throughout Northern Virginia. The company also owns finance and mortgage banking subsidiaries in Maryland.

Waverly Press Inc. of Baltimore reported a 3 percent drop in earnings for the quarter, a drop to $1.15 million (31 cents) from $1.18 million (33 cents) in the year-ago period. But the company's sales for the period increased to $19.4 million from $18.1 million last year.

Waverly's earnings for the first nine months of the year were $2.7 million (75 cents), up from $2.6 million (72 cents) for the same period in 1986. The company's sales for the period were $56.4 million, compared with $51.2 million last year.

The introduction of new equipment and systems, coupled with "production inefficiency" in its printing operations, were the primary culprits in the quarterly earnings decline, Waverly officials said.