RCA Corp.'s first-quarter profits jumped 29 percent from a year earlier despite a modest 1.7 percent revenue gain, the company reported yesterday.

RCA said the improved results reflected higher earnings from its broadcasting, defense and record-video operations. In particular, RCA said profit at its National Broadcasting Co. unit nearly tripled from a year ago.

However, earnings fell at RCA's consumer electronics and Hertz Corp. auto rental units, reflecting severe pricing competition in those industries, RCA said. The company's communications division posted flat results.

Meanwhile, first-quarter earnings rose by 13 percent at BankAmerica Corp., the nation's second-largest bank holding company, and by 31 percent at Chase Manhattan Corp., the third-largest, according to reports released yesterday. And in Chicago, Continental Illinois Corp. said that its first-quarter earnings topped those for the previous three months.

Among other companies reporting earnings yesterday were Nynex Corp., Allied Corp. and United Technologies Corp.

Overall, RCA's net income rose to $65 million (58 cents a share) in the first quarter from $50.3 million (40 cents) a year earlier. In the 1984 quarter, RCA took a $175 million write-off to reflect its decision to fold production of its videodisk player. RCA managed a profit in that quarter, however, thanks to a $75.7 million accounting change.

This year's first-quarter revenue totaled $2.40 billion, up from $2.36 billion.

RCA's financial performance has improved substantially over the past two years following RCA's decision to divest most of the assets that are unrelated to its three core industries of broadcasting, electronics and communications.

An exception to that strategy is Hertz, which has remained attractive because of the investment tax credits and depreciation allowances that it generates.

But in the latest quarter, Hertz's profit was "off substantially," depressed by "a combination of a highly competitive domestic car-rental market and lower profits from the sale of used cars," Robert R. Frederick, RCA's president and new chief executive, said at a meeting with securities analysts.

Frederick also said that near-term "profit improvements will be difficult to achieve" at Hertz because of continued downward pressure on prices.

The same is true in RCA's consumer electronics business, which includes television sets and videotape recorders, he said. Because of the heavy competition from Far East suppliers, "We simply must do an even better job of lowering costs" to bolster earnings, he said.

RCA's solid-state division also struggled in the latest quarter, reflecting the industrywide slump in sales of semiconductors and other integrated circuits, Frederick said.

The broadcasting division continued to improve, however. Although RCA does not break out the quarterly results of its various operations, it said NBC's first-quarter earnings were the highest in its history, as were those for the TV stations that RCA owns.

* San Francisco-based BankAmerica Corp., holding company for Bank of America, earned $114 million (63 cents a share) in the first quarter, up from $101 million (55 cents) in its 1984 first quarter.

BankAmerica said the earnings gain reflects "increasing benefit from our investments in restructuring our business."

President Samuel H. Armacost said "loan losses in the first quarter remained at higher-than-normal levels and included large charge-offs in the commercial real estate and shipping sectors."

BankAmerica added $58 million to its loan loss reserve to cover problems with faulty mortgage loan pools for which it had served as agent, increasing the total reserve to $95 million. Net loan losses rose to $221 million in the first quarter from $120 million in the same period a year before.

Primary capital ratio was 6.2 percent, up from 5.06 percent last year. Return on average assets was 0.39 percent, up from 0.34 percent; return on shareholders equity averaged 8.89 percent compared with 7.84 percent.

BankAmerica's total assets were $117.96 billion at quarter's end.

* Chase Manhattan Corp.'s first-quarter earnings of $133.9 million ($2.92 a share) were up from $102.5 million ($2.55) in the first quarter of 1984 despite a hike in loan loss provisions to $95 million from $75 million, reflecting higher charge-offs of $74 million compared with $51 million.

Chase's results included nonrecurring income that, after subtracting an unusually large decline in bond trading profits, equaled a net gain of roughly 45 cents a share.

"If you pull out the nonrecurring factor, it wasn't a breakaway quarter for Chase," said Lawrence Cohn, a banking analyst at Dean Witter Reynolds. "But it was a good, solid earnings gain given that they've built loss-reserve and primary capital."

Primary capital was 6 1/2 percent of assets, up from 5.54 percent. Return on average assets rose to 0.63 percent from 0.51 percent; return on shareholders equity was 13 percent, up from 11.7 percent.

Chase had assets of $78.88 billion.

* Continental Illinois Corp. earned $39.3 million (14 cents a share) in the first quarter compared with $36.6 million (12 cents) in the fourth quarter last year.

Continental did not release year-to-year comparisons, which it said were not meaningful because of the company's financial restructuring last year.

Continental's nonperforming loans were lower. But the company said it still relies heavily on the Federal Reserve Bank of Chicago and commercial banks for funding. It averaged $965 million in daily borrowings from the Fed, down from $3.8 billion in the previous quarter.

* Nynex Corp.'s first-quarter profit rose 16 percent from a year earlier on a 9.6 percent gain in revenue, Nynex said yesterday.

Nynex is one of the seven holding companies formed in January 1984 to operate the 22 telephone companies divested from American Telephone & Telegraph Co. Nynex's units provide service for most of New England.

The latest figures are the first year-to-year comparisons that Nynex and the six other companies have been able to report.

Nynex said its first-quarter net income climbed to $257.4 million ($2.55 a share) from $221.7 million ($2.29) a year earlier as revenue rose to $2.50 billion from $2.28 billion.

"The New York-New England economy continues to be vigorous, and demand for our products and services remains strong, with customer access lines up by 102,000 during the first three months of 1985," Nynex Chairman Delbert C. Staley said.

Staley said Nynex's diversification efforts also bolstered the company's results. Nynex has expanded into mobile-telephone service, and recently signed contracts to sell computers and other office-automation products made by Data General Corp. and Wang Laboratories Inc. Nynex also has opened two retail outlets to sell telecommunications equipment and information systems to small businesses.

Allied Corp.'s first-quarter net income was $134 million ($1.37 a share), an increase of less than 1 percent from $133 million ($1.36) in the 1984 first quarter. Sales were $2.9 billion, which also is less than 1 percent more than a year ago, when the total was $2.8 billion.

Chairman Edward L. Hennessy Jr. said that first-quarter after-tax operating income from the company's five sectors increased to $152 million from $146 million last year.

He said that reflected good performance by the aerospace sector, continued improvement in the industrial and technology sector, and higher profit for the oil and gas area. Performance of the automotive and chemical sectors was lower than the 1984 first quarter.

During the first quarter of 1985, Allied's capital expenditures totaled $135 million compared with $106 million in 1984, officials said.

* United Technologies Corp. yesterday reported slight year-to-year increases in first-quarter net income and revenue, highlighted by results from its Pratt & Whitney aircraft engine and Automotive Group segments.

Net income was $137.6 million (99 cents a share, fully diluted), up 3 percent from $133.5 million (97 cents), as sales were 1 percent higher at $3.92 billion, up from $3.8 billion.

Chairman Harry J. Gray said results for the quarter were helped by lower manufacturing costs at UTC, the seventh-largest manufacturer in the United States.