Eastman Kodak Co. yesterday announced lower earnings for the second quarter of $135 million (84 cents a share) compared with $140.3 million (87 cents) a year ago.

Meanwhile, Polaroid, Kodak's chief competitor in the domestic photography field, reported an increase in second-quarter earnings from $18.5 million (56 cents a share) last year to $20.5 million (62 cents) in this year's second quarter.

The two companies have been battling it out in the instant-picture market, which Kodak entered last year in an effort to unseat Polaroid, which pioneered instant cameras two decades ago. Kodak's entry, however, has not been as successful as the company had hoped.

Kodak reported increased sales for the second quarter of $1.3 billion, up from $1.2 billion a year before. Polaroid old sales also went up, to $249.3 million from $228.1 million.

Officials of Kodak, based in Rochester, N.Y., said the drop in earnings was due to higher operating costs and wages, despite a rise in volume and prices.

American Airlines reported increased profits and revenues for June, the second quarter and first half compared with the same periods last year.

June net income was $16.8 million (55 cents a share) compared with $14.6 million (51 cents) a year ago, as revenues rose from $179.3 million to $198.8 million.

In the second quarter, net income was $34.2 million ($1.09) on revenue of $558.5 million compared with net income a year earlier of $24.8 million (87 cents) on $500.5 million in revenues.

This brought first-half net income to $35.7 million ($1.13) and sales revenue to $1.06 billion compared with 1976 first-half net income of $16 million (56 cents) and revenue of $940.8 million.

Braniff International Corp., the Dallas-based airline, announced a rise in second quarter net earnings to $9.7 million (48 cents a share) from $6.2 million (31 cents) a year ago.

Revenue was $192 million in the second quarter, up from $165.3 million in the similar period last year.

General Telephone & Electronics Corp., a diversified communications firm, said earings, telephone revenues and products sales established records for the second quarter and first half of 1977.

Second-quarter net earnings per share increased 22 per cent to 94 cents from 77 cents a year ago, and first-half per-share earnings rose 34 per cent to $1.89 from $1.41.

Net income applicable to common stock was $126.15 million for the quarter compared with $100 million in the second quarter last year. For the half, income was $251.5 million compared with $180.94 million for the same period in 1976.

Total revenues and sales for the quarter were $1.88 billion compared with $1.64 billion last year. For the half, revenues came to $3.65 billion compared with $3.2 billion last year.

INA Corp., holding company for Insurance Co. of North America, reported net earnings for the second quarter of $43.7 million ($1.88 a share), against $17.6 million, (76 cents) a year ago.

The Philadelphia-based company had revenue in the second quarter of $886.2 million, up from $709.6 million a year ago.

Monsanto Co., a leading maker of chemicals and synthetic fibers, reported a 17 per cent decline in second-quarter net income on higher revenue.

Net income was $81.5 million ($2.21 a share) compared with $98.4 million, ($2.69) in the 1976 quarter. Sales rose 5.5 per cent to $1.122 billion from $1.063 billion.

For the first six months of 1977, net income was $229.4 million ($6.22) compared with $255.3 million ($7.09) in 1976. Sales were $2.428 billion compared with $2.237 billion for the first half of 1976.

American Can Co., the large container-manufacturing firm whose products include Dixie cups, reported that net earnings in the second quarter of this year had risen 16 per cent over last year.

Second-quarter net for the Greenwich, Conn., company was $29.5 million ($1.50 a share), up from $24.9 million ($1.26) a year ago. Sales were $925 million, up from $796.4 million.

Net earings for Sperry Rand Corp. for the first quarter ending June 30 were $37.5 million ($1.08 a share), up from $34.8 million ($1) a year ago.

Total sales for the computer and electronics firm were $827.9 million, up from $788 million.

American Brands, Inc., reported a net earnings increase in the second quarter to $41.5 million ($1.55 a share) from $32.4 million ($1.21) a year ago.

Sales for the conglomerate, whose products include Lucky Strike cigarettes, Master locks and Jergens lotion, were $1.1 billion in the quarter, up from $1 billion.

Nabisco, Inc., reported a drop in second-quarter net earnings from $17.8 million ($1.12 a share) last year to $7.5 million (47 cents) in the most recent quarter. The company attributed much of the drop to discontinuation and cutbacks of divisions.

Sales for the diversified East Hanover, N.J., company, whose products include Ritz crackers and Oreo cookies, rose in the second quarter to $503.9 million from $479 million a year ago.