Xerox Corp., a leading office-products and computer company, reported yesterday that its fourth-quarter profits rose 11 percent, in part because of a sharp gain in earnings from sales of office products.

Net income for the period rose to a record $142.2 million ($1.68 a share) from $127.8 million ($1.52) in the year-earlier period, while revenues jumped 19 percent to $2.228 billion from $1,868 billion in the fourth quarter of 1979.

The company's revenues from worldwide rental and service jumped 11 percent in the quarter, while revenues from the sale of copiers, duplicators and other office products rose 33 percent, Chairman C. Peter McColough said.

Xerox's 1980 earnings rose 10 percent to $619.2 million ($7.33) from $563.1 million ($6.69) a year earlier. Revenues increased by 17 percent to $8.196 billion from $6.996 billion in 1979.

McColough said he expects the company to register similar earnings gains this year, "assuming the economies of the major countries where we do business do not significantly weaken . . ."

Allied Chemical Corp. said yesterday that it earned $289 million ($8.15) a share) last year, up from only $11 million (20 cents) in 1979 after large write-downs and divestitures. The 1979 profit on operations that have continued was $5.95 a share. Sales were $5.519 billion, up 32 percent from $4.332 billion in 1979.

Net income for the final quarter was $81 million ($2.27) on sales of $1,448 billion compared with $67 million ($2.20) a year earlier on sales of $1.298 billion. The sales gain was 12 percent.

Chairman Edward L. Hennessy Jr. said soda ash and agricultural chemicals, including fertilizers, produced the best gains, although oil and gas operations also had better results and the company benefited from lower interest charges. In the other divisions, Converse Footwear's profits were better, but the electrical and phototypesetting divisions did not do as well as in 1979.

Quaker Oats Co. said yesterday that earnings for its second quarter ended Dec. 31 leveled off at $22.4 million ($1.06 a share) from $22.5 million ($1.06) a year ago. Sales were $690.3 million, up 12 percent from $617.3 million.

First-half earnings were $45.1 million ($2.12) on sales of $1.33 billion compared with earnings a year earlier of $46.4 million ($2.19) on sales of $1.19 billion.

A company statement said net income for the second quarter and first half were affected adversely by higher interest expenses on short-term borrowings and foreign currency exchange-transaction losses. Quaker Oats is an international marketer of foods, pet foods, toys, specialty chemicals, yarn and art needlecraft kits.

High interest rates, adversely affecting sales of boats and outboard motors principally slashed 1980 earnings of Brunswick Corp. to $23.92 million ($1.01 a share) from $51.42 million ($2.39) in 1979. Sales fell from $1.257 billion in 1979 to $1.2 billion last year.

Fourth-quarter profits tumbled to $8.37 million (37 cents) on sales of $305.99 million from $12.92 million (60 cents) a year earlier on sales of $311.92 million.

The 1980 earnings were increased 45 cents a share by pension accounting changes and expanded use of last-in, first-out inventory accounting.