Software AG Systems Inc. of Reston, a developer of advanced software, said earnings for its third quarter ended Feb. 28 were down slightly to $1.3 million (22 cents a share) on sales of $12 million from $1.7 million (27 cents) on sales of $10.5 million a year earlier.

Nine-month earnings were $5 million (83 cents) on sales of $36.7 million, compared with $4 million (66 cents) on sales of $30 million for the same period last year.

The strengthening of the U.S. dollar has affected international business and slowed growth from the first six months of the fiscal year, said Stuart J. Miller, president of the company. An advertising program and domestic sales force expansion also contributed to the results, he said.

* Survival Technology Inc. of Bethesda said earnings for its quarter ending Jan. 31 were $167,900 (6 cents a share). The company, which manufactures medical devices and sells services for emergency health care, principally in the areas of chemical agents and cardiac care, lost $414,600 (16 cents) in the same quarter last year.

Sales for the quarter were $6.596 million, 16 percent above the $5.668 million in sales for the comparable quarter.

* Questech Inc. of McLean said its earnings rose 9 percent last year to $1.129 million from $1.036 million in 1983. But per-share earnings fell from 84 to 79 cents because a public stock offering in May increased the number of shares outstanding.

Revenue for the engineering firm, which specializes in defense and aeronautics, was $32.972 million last year, a 21 percent increase from $27.178 million in 1983.