Rising jet fuel prices produced first-quarter losses of $74.9 million for Pan American Air World Airways and $22 million for Braniff International Corp., the carriers said yesterday.

Pan Am's results, which include operations of the former National Airlines, compare with an $8.9 million loss in the first three months of 1979, Chairman William T. Seawell said.

"Pan Am . . . has been severely affected by skyrocketing fuel prices," Seawell said in a prepared statement."We have been frustrated in our efforts to obtain fare increases to offset these costs . . ."

The company's operating revenues for the period jumped 18.6 percent to $800.6 million from 1979 first-quarter revenues, while expenses reached $863.8 million. Seawell said jet fuel and oil accounted for $271.1 million, or 31.4 percent of the expenses.

Braniff's first-quarter loss compared with 1979 first-quarter profits of $8.1 million (40 cents a share). Revenues increased from $283.5 million to $372.1 million.

Aetna Life & Casualty Co. reported operating earnings of $122.7 million ($1.52 a share) for the first quarter compared with $122.9 million ($1.52) a year earlier.

Aetna is the nation's largest diversified financial company.

"Total revenue rose 33 percent to $3.5 billion largely due to strong sales of group pension products in the first quarter," he said.

First-quarter net income was $127.9 million ($1.58) compared with 1979 first-quarter net income of $124 million ($1.54). Those figures included capital gains this year and an extraordinary tax credit a year ago.