Northrop Corp.'s sales for 1976 passed the $1 billion mark for the first time in the company's 38-year history, due largely to a marked increase in aircraft sales.

Northrop, in announcing a boost in its quarterly dividend to 50 cents from 35 cents, predicted that record results in 1976 should lead to "significant gains" again this year.

The industrial firm's sales for the year ending Dec. 31 reached $1.26 billion, and increase of 28 per cent over the $988 million reported in 1975. Net income for Northrop was $36.3 million, 47 per cent more than the $24.7 million reported in 1975.

Thomas V. Jones, chairman and chief executive officer, said the record year reflects greater F5 aircraft program sales volume, burgeoning support services business and continuing growth in productivity, which has averaged more than 6 per cent annually for more than a decade in the company's major manufacturing operations.

Primary earnings per share for 1976 totaled $5.76, 33 per cent more the year, Northrop had sales for $351.4 million, 25 per cent more than the $281.6 million logged in the final quarter of 1975. Net income for the final quarter was $15 million compared with $7.3 million a year ago.

Fourth-quarter earnings for Occidental Petroleum Corp. last year were four times higher than in 1975, the firm has announced. Occidental is the nation's 11th largest oil company.

The firm said net earnings for the last quarter of 1976 were $17.7 million ($1.14 a share) on sales of $1.6 billion. In the previous year, the firm earned $17.7 million (20 cents) on sales of $1.1 billion.

Net income for all of 1976 was $183.7 million, up 7 per cent from the $172 million it earned in 1975.

Company officials said the 1975 fourth-quarter earnings were depressed by a shutdown of Occidental's Libyan operations and a year-end charge against earnings of $19 million as a result of write-offs in Nigeria and Venezuela. Libyan operations were at an unusually high level in the last quarter of 1976, the firm said.

The Upjohn Co. has reported that sales and earnings in 1976 were in the highest in its 90-year history.

Sales were $1.025 billion, up 15 per cent over previous record sales of $890.7 million in 1975, officials said.

Net earnings rose 16 per cent to $77.6 million ($2.62 a share) from $66.7 million ($2.62) in 1975.

Sales for the fourth quarter of 1976 were $257.8 million, a record for the quarter and a 14 per cent increase from sales of $226.5 million for the year-earlier period. Fourth-quarter net earnings also set a record at $14.8 million. (50 cents), up 11 per cent from 1975 fourth-quarter earnings of $13.3 million (45 cents).

Playboy Enterprises, Inc., has reported a sharp upturn in earnings for the last six months of 1976, and a company official predicted earnings would continue to increase.

Net earnings for the period, which was the first half of Playboy's current fiscal year, totaled $5.12 million (56 cents a share) compared with $1.558 million (17 cents) for the same period in 1975. Revenues increased from $99.151 million to $116.448 million, Playboy said.

Net earnings for the second quarter of the fiscal year increased from $659,000 in 1975 to $1.352 million in 1976.

Derick J. Daniels, president and chief operating officer of Playboy, attributed the improvement to higher earnings from Playboy clubs in England and increased profitability of Playboy magazine.