BankAmerica Corp., whose principal subsidiary, Bank of America, is the nation's largest bank, yesterday reported a 33.3 percent decrease in third-quarter earnings before securities transactions to $118.3 million (80 cents a share) from $176 million ($1.20) in the same period last year.

In the first nine months, BankAmerica earned $349.3 million ($2.37) before securities transactions, down from $484.2 million ($3.30) a year ago.

Samuel H. Armacost, president of the San Francisco-based bank holding company, cited the effect of persistently high interest rates on the corporation's funding position as the main reason for the decline. Bank of America has huge fixed-rate assets such as mortgages, which were written at lower rates and must be funded at today's higher costs.

Occidental Petroleum Corp., the 11th-largest U.S. oil company, reported yesterday that its third-quarter profits dropped 13.3 percent in face of the global oil glut.

Analysts have predicted the major oil companies' third-quarter earnings would be about equal to year-earlier results because worldwide crude oil prices have fallen by $2 a barrel.

Occidental--the first major refiner to announce its third-quarter showing--earned $115.8 million ($1.15 a share), down from $133.7 million ($1.62) in the same period last year. Occidental had 11.6 million more shares outstanding in the latest quarter than in the 1980 third quarter.

Third-quarter sales rose by 23 percent to $3.7 billion from $3 billion a year ago.

Occidental said higher interest costs and "the continuation of worldwide crude oil surpluses resulted in lower net for the quarter."

Occidental, which has a large oil-production-sharing agreement with Libya, recently said it had made new arrangements with the north African nation that would enable the company to market Libyan crude more profitably.

Occidental's coal operations and the Aug. 12 acquisition of Iowa Beef Processors Inc. contributed to its third-quarter results, which also included a gain of about $7 million from the sale of an investment in a joint real estate venture.

For the first nine months of 1981, Occidental's net earnings fell 20.3 percent to $456.1 million ($5.15) from $572.7 million ($7.19) a year earlier. Revenues climbed 9.6 percent to $10.2 billion from $9.3 billion.

United Technologies Corp., one of the nation's largest military contractors, said yesterday its third-quarter profits rose 15 percent on a 12 percent revenue gain that included sharply higher government sales.

Profits totaled $112.53 million ($1.70 a share) compared with $98.03 million ($1.62) for the same period last year. Sales rose to $3.26 billion from $2.90 billion.

Profit growth was lower in the third quarter than in the year's first two quarters, said Harry J. Gray, chairman and president. But military, general aviation, air conditioning, helicopter and automotive business "performed well," while the corporation's semiconductor business suffered losses, he said.

The corporation said sales to the federal government during the first nine months of its fiscal year were up 51 percent over the first three quarters of 1980 to $2.79 billion from $1.85 billion. Commercial and industrial sales were up 6 percent to $7.26 billion from $6.93 billion.

Nine-month profits rose 18 percent, from $290.85 million ($4.81) to $342.31 million ($5.30), and sales were $10.16 billion, up 16 percent from the previous year's $8.78 billion.

Burlington Northern Inc. said yesterday that its third-quarter net income rose 59 percent from a year earlier.

Burlington Northern operates the nation's longest rail line and has interests in trucking, forest products manufacturing, coal and minerals and land and real estate.

The parent company said it earned $63.6 million ($1.63 a share) in the third quarter compared with $40 million ($1.19) in the same quarter last year.

Revenues in the latest quarter totaled $1.27 billion, including results of the former St. Louis-San Francisco Railway Co., known as the Frisco. The line merged with Burlington Northern Railroad last November. Revenues for the BN in the same quarter last year were $1.04 billion.

Nine-month net income was $193 million ($4.96) compared with $157.9 million ($4.79) in the first nine months of 1980. Revenues increased by 30 percent to $3.7 billion from $2.86 billion.

President Richard M. Bressler said that coal traffic rose during the latest quarter, but softness in grain and lumber shipments continued.