Communications Satellite Corp. (Comsat) yesterday reported net income of $7.7 million (97 cents a share) for the second quarter, down from $8 million (80 cents) a year earlier.The decrease was primarily the result of a change in accounting policy affecting allowance for money used during construction, the corporation said.

Comsat's revenues during the second quarter were $43.7 million, an increase of $1.7 million that came mainly from television and temporary services as well as "growth in Marisat system revenue."

First-half earnings totaled $15.5 million ($1.94) compared with $17.7 million ($1.78) last year. The 1977 earnings per share include 15 cents that would have been eliminated by subsequent accounting changes, the company said. Revenues for the first half stood at $85.9 million, up from $84 million.

The Comsat board declared a regular quarterly dividend of 50 cents a share to be paid Sept. 11 to shareholders of record Aug. 11.

A. H. Robins Co. reported an increase in net income of 7 percent for the second quarter, from $6.9 million (25 cents a share) to $7.4 million (29 cents). Sales for the Richmond-based pharmaceutical manufacturer during the three months ended June 30 totaled $86.9 million, up 16 percent from the $74.9 million in sales reported a year earlier.

First-half net income amounted to $16.4 million (63 cents), up 20 percent from the $13.6 million (52 cents during the first half of 1977. Sales during the half rose 19 percent to $176.3 million.

The company said expenses incurred by settlements of lawsuits involving the Dalkon Shield contraceptive device it once manufactured "will continue to be high for at least the remainder of the year." These expenses reduced first-half earnings by 8 cents a share, 3 cents of which was taken in the second quarter.

United Services Life Insurance Co., a Washington company that specializes in insurance for military and retired military offices, reported record operating earnings for the second quarter of $2.1 million (66 cents a share), up from $1.6 million (50 cents) a year earlier. Life insurance in force topped $2.8 billion for the first six months, an increase of more than $66 million, the company said.

Black and Decker Manufacturing Co. of Towson said its earnings for the third quarter ended June 25 were up 38 percent from $12.3 million (30 cents a share) to $17 million (40 cents). Sales for the quarter rose 15 percent from $205.3 million to $237 million, the tool manufacturer said.

Nine-month earnings rose 29 percent from $39.2 million (94 cents) to $50.8 million ($1.21), while sales were up 15 percent to $721.9 million.

Black and Decker's board declared a quarterly cash dividend of 15 cents a share to be paid Sept. 25 to stockholders of record Sept. 11.

Chesapeake Corp. of Virginia reported that second-quarter earnings dropped from $3.3 million ($1.18 a share) to $2.6 million (92 cents), while sales rose from $34.95 million to $41.2 million. The decrease in earnings for the three months ended June 18 and for the first half was largely the result of a decrease of $1.8 million in investment tax credits.

For the first half, earnings dropped from $5.5 million ($1.99) to $4 million ($1.41). Sales rose from $69.6 million to $79.5 million.