Led by its rental car operation, RCA Corp. profits for the first quarter were the best ever for the period, the company said yesterday. It was the company's fifth consecutive quarter of record profits.

Edgar Griffiths, president and chief executive officer, noted the achievement came despite the unusually severe winter weather, energy cutbacks forced by the coal strike and an earnings decline by its National Broadcasting Co. unit. He predicted that 1978 would be "another record year" for the company.

Earnings came to $54.9 million (72 cents a share) against $48.5 million (63 cents) in the 1977 period. Sales were $1.5 billion, up from the $1.37 billion last year.

For the first time, RCA's Hertz Corp. displaced NBC as the firm's best profit source. Hertz profits were a third higher than the year-earlier figure, RCA said.

Seven of the companys operating units chimed in with record profits while four others improved from the others at new highs were RCA Records, Coronet Industries, the Oriel Foods group, solid state, commercial systems and picture tubes.

International Paper Co., the largest U.S. paper manufacturer, reported a 19 percent increase in profits for the first quarter and a 13 percent rise in sales.

The company attributed the gains to increased demand in the market-place for its products and tight control over cost production.

It also hinted at the possibility of price increases in the near future on some of its products.

For the period ended March 31, profits rose to $57.9 million ($1.23 a share) from $48.6 million ($1.04) in the same period a year earlier. Sales climbed to $958 million from $850 million in the 1977 period.

In making the announcement, the company said a high level of demand resulted in price increases on many of its products, "but much needed price increases have not been made on some major product lines," including forest products, linerboard, commodity paper pulps and corregated containers.

Kaiser Aluminum & Chemical Corp. reported that net earnings in the first quarter of 1978 were $24.5 million ($1.20 a share), slightly above earnings of 23.9 million ($1.28) in the same period last year.

A loss of $6.1 million (31 cents), due to translation of long-term foreign exposures, is included in the earnings report.

Sales in the first quarter of 1978 totaled $548.2 million, compared with $522.6 million a year ago.