BankAmerica Corp., whose Bank of America is the nation's biggest commercial bank, said yesterday that its fourth-quarter net earnings plummeted 47.4 percent to $84.6 million.

President Samuel H. Armacost attributed the slide in earnings to high interest rates and governmental deregulation policies.

Fourth-quarter profits equaled 57 cents a share and compared with 1980 fourth-quarter earnings of $161.8 million ($1.09 a share). For the year, net income was $445.5 million ($3.02), down from $643.4 million ($4.38).

Citicorp, the nation's largest bank holding company and operator of the second-largest commercial bank, Citibank, reported that income for the fourth quarter was $217 million ($1.71 a share), more than twice the $96 million (77 cents) earned in the same quarter a year ago. But for the year, net rose only 9 percent to $555 million ($4.40) from $499 million ($4.08).

Citicorp said growth in fees and commissions offset a decline in net interest revenue and higher expenses.

General Electric Corp. reported yesterday that its earnings for the fourth quarter rose 10 percent from a year earlier to $452 million ($1.99 a share), while those for the full year were up 9 percent from 1980 results despite a 7 percent decline from its consumer products operations.

GE Chairman John Welch cited gains from interests in natural resources, financial services, engineered materials, power systems, aircraft engines and industrial products.

Fourth-quarter earnings in 1980 were $411 million ($1.80). Sales rose 9 percent to $7.56 billion from $6.92 billion in the fourth quarter of 1980.

For all of 1981, earnings rose to $1.652 billion ($7.26) from $1.514 billion ($6.65). Sales also rose 9 percent to $27.24 billion from $24.96 billion the previous year.

Westinghouse Electric Corp. of Pittsburgh reported increased earnings and sales for 1981, although earnings in the fourth quarter fell behind year-earlier results.

Each of its three major operating companies--public systems, industry products and broadcasting -- exceeded 1980 sales.

Net income was $438 million ($5.10 a share) last year, up from $402.9 million ($4.71) in 1980. Sales climbed to $9.367 billion from $8.514 billion.

Fourth-quarter earnings were $103.1 million ($1.20), down from $107 million ($1.25). Sales rose to $2.527 billion from $2.265 billion.

General Foods Corp., the nation's largest manufacturer of packaged foods, said its profits fell 31.7 percent in the third quarter ended Dec. 26 to $40.7 million (83 cents a share). It cited high advertising expenses and a loss on the sale of its Burger Chef restaurants.

Earnings a year earlier were $59.6 million ($1.20). Sales rose 33 1/2 percent to $2.11 billion from $1.58 billion.

Nine-month earnings fell 19 1/2 percent to $147.3 million ($2.98) from $182.9 million ($3.67). But sales rose 27.4 percent to $6.23 billion from $4.87 billion.