As consumer and real estate loans showed strong growth, BankAmerica Corp.'s net income increased 20.5 percent to $600 million in 1979 from $498 million the year before, the company said yesterday.

President A. W. Clausen said income before securities transactions topped $600 million in 1979 compared with $514 million in 1978.

The growth follows a 30.2 percent increase attained in 1978 and represents the 17th consecutive year of earnings growth, officials said.

Per-share income before securities transactions for 1979 was $4.10 compared with $3.53 in 1978. Net income also was $4.10 a share, up from $3.41 in 1978. w

Fourth-quarter consolidated income before securities transactions rose 7.8 percent to $158 million over 1978's strong fourth quarter. On a per-share basis, income before securities transactions was $1.07 for the fourth quarter of 1979, up 7 percent from $1 earned a year earlier.

While 1978's growth reflected both an increase in earnings assets and an expanding net interest revenue margin, recent growth has been increasingly dependent on a higher volume of assets to overcome declining margins, officials of the nation's biggest bank said.

RCA Corp. announced a 6.8 percent decline in fourth-quaarter 1979 net income but said its profits increased by 1.9 percent for all of 1979.

The company attributed its showing to large increases in research spending on its home video disc system, lower earnings for the National Broadcasting Co. division and a severe business decline at RCA records.

RCA earned $70.1 million (92 cents a share) in the fourth quarter against $75.2 million (99 cents) a year ago. Revenues rose to $1.98 billion from $1.85 billion.

For the year, RCA's earnings came to $283.8 million ($3.72) against $278.4 million ($3.65) in 1978. Sales rose to $7.45 billion -- RCA's first $7 billion year -- from 1978's $6.6 billion.

Armco Inc. reported higher 1979 sales and earnings, and noted good performance from its specialty steel products and fabricated metal products.

The preliminary unaudited results show earnings of $221 million ($4.82 a share) for 1979 on sales of $5.03 billion compared with earnings of $198 million ($4.29) on sales of $4.3 billion for 1978.

Armco is the nation's third largest steel producer.