RCA Corp. said yesterday that its fourth-quarter net income jumped 37 percent to $102.8 million from $74.9 million last year, thanks to strong gains in its electronics and broadcasting operations.

In other earnings reports yesterday, Eastern Airlines, which persuaded its unions to accept hefty pay cuts last year, said it narrowed its losses for 1984 to $37.9 million and earned a net profit of $10.7 million in the final three months.

United Press International released preliminary financial results for the fourth quarter of calendar year 1984 showing a profit of $1.1 million, a milestone for the news agency, which has operated in continuous deficits since 1963.

American Express Co. said it earned $169.5 million in the fourth quarter, sharply reversing a year-earlier loss of $21.9 million.

* RCA Corp.'s per-share profit for the period ended Dec. 31 came to $1.03, compared with 70 cents a year earlier.

RCA, which produces electronic products and owns the NBC television network and Hertz car rental chain, said revenue for the three months rose 12.5 percent to $2.79 billion from $2.48 billion.

For the year, RCA reported net income of $341 million ($3.30 a share), up 50 percent from $227 million ($1.93) in 1983. Revenue rose 12.6 percent to $10.11 billion from $8.98 billion.

The year's results reflect a reduction in the first quarter of $175 million for the company's phaseout of production of videodisc players and the addition of $75.7 million from a change in its accounting methods.

* Eastern Airlines has not made a year-end profit since 1979, but its fourth-quarter earnings are its second consecutive quarterly net profit.

"Eastern is clearly on the right track, as evidenced by the trend of reduced losses, increased operating profit, and a net profit in the past two quarters," Eastern Chairman Frank Borman said yesterday.

Miami-based Eastern said the fourth-quarter profit of $10.7 million compared with a $54.8 million net loss in the fourth quarter of 1983.

The airline also reported an operating profit of $69 million for the fourth quarter, the highest quarterly operating profit in the company's history. Year-end figures showed the company reduced its net loss from $183.7 million in 1983 to $37.9 million.

Eastern saved $370 million last year by persuading its 37,000 employes to take pay cuts of 18 to 22 percent.

The airline said earnings per share for the fourth quarter rose to 9 cents, compared with a loss of $1.71 per share in the fourth quarter of 1983.

* UPI reported that fourth-quarter revenue totaled $25.4 million against operating expenses of $24.3 million. The fourth-quarter profit of $1.1 million represents a marked improvement in the news agency's financial performance. In the fourth quarter of 1983, UPI lost $6.5 million.

"Achieving a profit is a dramatic and tangible step forward for UPI, demonstrating this company's ability to operate within its own means," said Luis G. Nogales, UPI president and chief operating officer. "This is a clear sign that UPI is on the right path for continued growth in 1985."

On Sept. 17, 1984, UPI journalists and photographers in the Wire Service Guild approved measures negotiated by company and guild officials that included temporary wage reductions, staff cutbacks and cost-containment measures. The plan required a 25 percent pay reduction for all employes for three months, with restoration to previous levels scheduled in increments every few months.

* American Express Co., whose investment unit is Shearson Lehman/American Express Inc., said fourth-quarter profit equaled 76 cents a share. Revenue jumped 38 percent to $3.50 billion, from $2.53 billion.

For all of 1984, American Express said earnings rose 18 percent to $609.6 million ($2.79 a share), from $514.7 million ($2.53) in 1983. Annual revenue increased 25 percent to $3.62 billion from $2.89 billion.

* Standard Oil Co. (Indiana) reported Monday that earnings in the final three months of 1984 nudged up 1.3 percent from a year earlier while profit for the full year jumped 17 percent to a record $2.183 billion.

Indiana Standard was the first of the nation's leading oil companies to report results for the fourth quarter, and its modest gain was expected to be one of the few bright spots for the industry.

Earnings in the fourth quarter rose to $465 million from $459 million in the same period a year ago. And while profit rose, revenue slipped, to $7 billion from $7.4 billion.

For all of 1984, profit surpassed the previous record of $1.922 billion set in 1981 and was up from the $1.868 billion in 1983.

* Rockwell International Corp. said yesterday that higher earnings by all four of its diversified core businesses contributed to a 53 percent earnings increase for its first fiscal quarter ended Dec. 31, 1984.

Net income for the quarter was a record $140.5 million (94 cents per share), compared with last year's first-quarter net income of $91.9 million (59 cents).

Sales in the first quarter of fiscal 1985 totaled $2.3 billion, up 17 percent from sales of $2 billion in the same period a year ago.