Higher earnings by most of its operations led RCA Corp. to a profit of $47.6 million (40 cents a share) in the third quarter compared with a year-earlier loss of $104.8 million, the company said yesterday.

In other third-quarter earnings reports yesterday:

* Warner Communications said its Atari home video products helped to propel earnings to a record.

* The recession and higher research and development costs cut profits at United Technologies Corp.

* Profits increased slightly at GTE Corp.

* Sales and earnings of PepsiCo set records.

* Caterpillar Tractor Co. sustained its first non-strike lost since the 1930s.

* Monsanto Co. net income topped year-ago levels by $15 million.

* American Cyanamid Co. profits dropped sharply.

* Armco Inc. said it lost money in the last quarter and expects the current one to be rough.

* Honeywell Inc. said profits topped year-earlier levels by 37 percent.

* Burroughs Corp. profits gained on a 27 percent rise in revenues.

RCA's 1981 third-quarter loss was on writedowns for restructuring and reevaluation of assets and was after a gain of $18.1 million on the sale of CIT Financial Services' headquarters building.

Revenue in the period rose to $2.04 billion from $1.99 billion.

Nine-month earnings were $168.6 million ($1.55) compared with a loss of $3.8 million a year earlier. Revenue climbed to $6.06 billion from $5.89 billion.

Chairman Thornton F. Bradshaw said that broadcasting, communications, CIT Financial Services and Hertz Rent-A-Car contributed strongly to the gains, but RCA consumer electronics products, appliances and commercial equipment business declined because of the recession and price competition. Bradshaw said he is particularly concerned about the deteriorating market for such consumer electronic products and radio and television receivers. He said sales of videodiscs continued to be strong.

In the latest quarter, NBC's earnings "exceeded those of the comparable quarter of 1981 without regard to the special write-down of program material in that quarter." NBC's increase mainly reflected "favorable marketing conditions for the television network and the owned-and-operated television stations," RCA said.

Warner Communications Inc. reported record earnings of $78.7 million ($1.21 a share) in the third quarter, and said the main factor was the continued rapid growth of its Atari video games operations.

Steven Ross, chairman of the entertainment and communications business, said earnings rose 34 percent from $58.6 million (91 cents) in the 1981 third quarter.

Revenue rose 18 percent to $1.03 billion from $872 million.

Warner Communications posted increases of 41 percent in the operating income from its consumer electronics division -- which includes Atari -- to $109.6 million and of more than 200 percent from its filmed entertainment division to $39.5 million, helped by the licensing of films to broadcasters.

But operating earnings declined from its music business, its Franklin Mint marketing unit and its publishing business.

Nine-month profits rose to a record $224.8 million ($3.46) on revenue of $2.87 billion from year-earlier profits of $150.7 million ($2.39) on revenue of $2.15 billion.

United Technologies Corp., the largest U.S. aerospace concern and 20th-largest industrial corporation, announced that its third-quarter profits fell because of the recession and higher research and development costs.

Profits dropped to $113.2 million ($1.78 a share) from $123.8 million ($2.05) in the same period last year as revenues rose slightly to $3.31 billion from $3.26 billion.

Nine-month profits rose to $420.89 million ($7.00) from $360.17 million ($6.20) but revenues declined to $10.03 billion from $10.16 billion.

The firm said it was hit by a decline in sales of its Pratt and Whitney engines to commercial airlines, while operations of its Carrier air conditioning, Essex and automotive group were depressed by the slump in the house construction and automobile sales. However, the Otis Elevator division made "strong profit growth" during the period.

GTE Corp. reported a slight increase in profits for the third quarter, which it said reflected the country's sluggish economy.

GTE, the second-largest utility company behind the giant American Telephone & Telegraph, said profits rose to $199.1 million ($1.11 a share) in the quarter from $175.0 million ($1.03) a year ago. Revenues showed the same small increase, to $2.98 billion from $2.72 billion.

Nine-month profits advanced to $598.1 million ($3.39) from $531.7 million ($3.21). Revenues were $8.91 billion compared with $7.96 billion in the 1981 period.

GTE said the quarter was marked by slower growth rates in long-distance calling and in new consumer telephone lines.

PepsiCo Inc. yesterday reported record sales and earnings for both the third quarter and the first nine months of 1982 as the growth of beverage and food products divisions in the domestic market more than offset declines in key international markets.

Third-quarter net income increased 11 percent to $113 million ($1.20 a share) from $102 million ($1.09) in the 1981 quarter. Sales rose 9 percent to $1.9 billion from $1.74 billion.

Nine-month net income increased by 13 percent to $273 million ($2.91) from $242 million ($2.62) in the same period last year. Sales increased to $5.27 billion from $4.86 billion.

Caterpillar Tractor Co. said that it lost $28.1 million in its third quarter -- its first non-strike loss since the early 1930s -- and the company projected a loss for the year.

The manufacturer of construction equipment said it expects "much lower" sales in the fourth quarter and projected "a significant after-tax loss for the full year."

A slump in sales, caused by the recession, was blamed for the third-quarter loss, along with high interest rates and the strengthening U.S. dollar, which means stiffer competition for overseas markets.

"Caterpillar's business is highly dependent on capital investment, which has been unusually depressed for an extended period of time," Caterpillar said. "This has caused a severe worldwide drop in user demand for the company's products."

The third quarter ended Sept. 28 and the United Auto Workers went on strike against Caterpillar Oct. 1. Talks are scheduled to resume Oct. 27 in St. Louis with a federal mediator.

Physical sales volume during the third quarter was 36 percent lower than the third quarter of last year. U.S. sales were down 26 percent to $777 million, and foreign sales of $919 million were down 35 percent.

Caterpillar's third-quarter loss came on sales of $1.7 billion compared with a profit of $174.3 million on sales of $2.46 billion during the third quarter of 1981.

For the first nine months, Caterpillar profits were 27 cents a share, compared with $5.46 a share for the first nine months of 1981. Sales for the first nine months were $5.51 billion, down $1.37 billion from 1981.

Monsanto Co. said yesterday that its net income for the third quarter was $71 million ($1.79 a share), an increase of $15.1 million from operating income for the same period in 1981 of $55.9 million ($1.34). In the 1981 period, the company had a $67.7 million gain from the sale to E.I. du Pont de Nemours & Co. of Monsanto's assets in a joint venture with Conoco Inc, boosting overall net to $123.6 million ($3.09).

Nine-month net income was $304.7 million ($7.67) compared with $393.4 million ($10.25) a year earlier.

Consolidated net sales for the quarter were $1.5 billion compared with $1.63 billion in the third quarter of 1981, while nine-month net sales were $4.86 billion compared with $5.39 billion in 1981.

"Despite the difficult farm economy in this country, our agricultural products business had a record third quarter," Chairman John W. Hanley said.

American Cyanamid Co. had a 48.2 percent drop in third-quarter profits from a year ago as global sales fell 7.9 percent.

Chairman James G. Affleck said the company's medical business is having an outstanding year but the global decline in markets for agricultural chemicals and its Formica products, the impact of currency devaluations in Mexico and Brazil and the adverse effect of the strong U. S. dollar on exports slashed earnings and sales.

Third-quarter profits fell to $27.1 million (56 cents a share) on sales of $861.2 million from $52.3 million ($1.09) a year ago on sales of $35 million. Nine-month earnings slipped to $93.2 million ($1.93) on sales of $2.608 billion from $148.7 million ($3.10) a year ago on sales of $2.722 billion.

Armco Inc. reported a net loss from operations of $52 million for the third quarter and said it expects a rough fourth quarter.

Armco, the nation's seventh-largest steel maker, said it had third-quarter sales of $1.2 billion. It also had special charges of $70.6 million, bringing its total net loss for the quarter to $122.6 million.

In the period a year ago, Armco had $67.1 million in net income on sales of $1.7 billion.

Armco said most of its loss came from its carbon-steel line, hit hard by the recession.

Honeywell Inc. reported that third-quarter earnings rose over 37 percent, but said that the company's businesses continue to be affected by the recession.

Net income was $43.8 million ($1.96 a share) compared with $32.4 million ($1.43) in the corresponding quarter of 1981. The 1981 figure was decreased by a $26.2 million loss but benefited from a $13.7 million tax credit.

Revenues rose to $134 billion from $1.27 billion last year.

Nine-month earnings, including capital gains of $66 million, were $184.9 million ($8.27) compared with $156.1 million ($6.89) in 1981. Revenues were $3.918 billion compared with $3.785 billion a year ago.

Burroughs Corp. reported net income of $36.13 million (86 cents a share) for the third quarter against $32.40 million (78 cents) a year earlier. Revenues were up 27 percent to $1.02 billion from $797.27 million.

For the nine months, the company earned $99.71 million ($2.37) on revenues of $3.06 billion against year-earlier earnings of $85.98 million ($2.07) on revenues of $2.38 billion.

"Our results are reflective of a soft economic environment both in the United States and internationally, as well as the continued strength of the U.S. dollar," Chairman W. Michael Blumenthal said.