Aluminum Co. of America yesterday posted earnings of $40.6 million (49 cents a share) for the second quarter compared with $112.8 million ($1.38) for the same period a year ago.

Sales and operating revenue for the 1985 quarter were $1.4 billion compared with $1.5 billion.

For the first half of 1985, Alcoa earned $47.3 million (57 cents) compared with $210.6 million ($2.58) for the first half of 1984.

Sales and operating revenue for the first half was $2.68 billion compared with $2.94 billion for the 1984 period. American Brands Inc. said second-quarter profits fell 10 percent from a year earlier on a 3 percent decline in sales.

*American Brands, a diversified packaged goods and services concern, makes Lucky Strike and Carlton cigarettes, Jim Beam bourbon, Master locks, Titleist golf equipment and Sunshine crackers and cookies.

In the second quarter, net income fell to $85.9 million ($1.48 a share) from $95 million ($1.64) a year earlier, the company said. Sales slid to $1.63 billion from $1.68 billion.

For the first half of 1985, American Brands' earnings fell 4 percent to $193.9 million ($3.36) from $201.8 million ($3.50). Six-month sales dropped to $3.36 billion from $3.51 billion.

*Lockheed Corp. earnings rose by 11.5 percent in the second quarter and 17.1 percent in the first half of the year, and the company predicted it will continue to show good gains over its record 1984 income.

For the latest quarter, the aerospace company earned $87 million ($1.32 a share) on sales of $2.2 billion compared with profits of $78 million ($1.21) on revenue of $1.93 billion a year earlier.

First-half profits were $171 million ($2.59) on sales of $4.35 billion vs. $146 million ($2.26) on sales of $3.52 billion.