Communications Satellite Corp., continuing to pump funds into its Satellite Business Systems partnership, reported yesterday a 33 percent decline in third-quarter profits. Separately, Virginia Electric and Power Co. announced a 9 percent profits rise and an increase in the company's quarterly dividend.

Although Comsat's profits rose $238,000 from this year's second quarter, profits fell to $6.38 million (80 cents a share) from $9.55 million ($1.19) for the 1980 third quarter.

Comsat's role as a one-third partner in SBS cost the company $5.9 million for the quarter, up $2.5 million from the firm's contribution to SBS in last year's third quarter. SBS, a partnership of Comsat, Aetna Life and Casualty and International Business Machines Corp., has launched two satellites in a $1 billion effort to corner a major portion of the business communications market.

The District company's sales for the quarter rose, however, to $84.9 million from $75.5 million this time last year. For the nine months, Comsat reported profits of $32.6 million ($4.08), up from $28.5 million ($3.57) in the corresponding 1980 period. Revenues rose to $244.4 million for the three quarters, up from $217.7 million last year.

Vepco, meanwhile, said third-quarter profits rose to $78.2 million (63 cents) from $71.6 million (60 cents) last year. Sales for the quarter dropped to $567.6 million from $576.5 million in 1980. Profits for the first nine months of the year rose one percent to $170.6 million ($1.27) from $168.8 million ($1.33).

The Richmond-based utility also increased its quarterly cash dividend on common stock to 37.5 cents a share from 35 cents a share, the first such hike in more than two years. The dividend is payable Dec. 21 to stockholders of record Nov. 30.

Media General Inc., which publishes Richmond's daily newspapers, reported record third-quarter and nine-months earnings, as profits for the quarter rose to $7.7 million ($1.08) from $6.8 million (95 cents). Sales for the period rose to $267.3 million from $245.4 million.

The company's profits for the first three quarters rose to $22.7 million ($3.18) from $20.7 million ($2.88) on sales of $267.3 million, which increased from $245.4 million in 1980.

In other reports, Robertshaw Controls Co. announced third-quarter profits of $2.1 million (62 cents) sharply up from third-quarter profits last year of $1.5 million (41 cents). Sales rose to $87.4 million from $82.3 million.

The company reported nine-month profits of $5.9 million ($1.69) compared with profits of $6.0 million ($1.55) for the same period in 1980. Sales at the Richmond-based firm rose to $268.5 million from 1980 sales of $256.9 million for the same period.

Software AG International, a Reston software and technology firm, which had said previously that it expected first-quarter earnings to decline, reported yesterday that profits per share had fallen to five cents from seven cents.

For the first quarter ending Aug. 31, Software AG had profits of $283.7 million, compared to $784.7 million for the similar period last year. Revenues for the period declined to $4.5 billion from $4.6 billion in 1980. The firm said it expected improvements in second-quarter results.