American Motors Corp. reported third-quarter earnings of $15.1 million (49 cents a share) yesterday, nearly five times year-ago earnings of $3.1 million (10 cents).

Net sales for the three months ending June 30 were a record $798 million, up 13.5 percent from $703 million a year ago.

Sales of Jeep vehicles also were down slightly at 49,666 this year compared with 50,141 for the same quarter in 1-78.

"Significantly improved third-auarter operating earnings, rising to $15.1 million from $3.1 million last year, reflect the actions taken to date to improve the company's operations," said AMC's chariman and chief executive officer, Gerald C. Meyers.

Net sales in the past nine months ending June 30 were $2.3 billion compared with $1.9 billion for the nine-month period the previous year. Net earnings so far for the 1979 fiscal year have been $73.3 million ($2.41) compared with net earnings in the 1978 nine months of $10.7 million (35 cents.)

Dow Chemical Co. earned $1.19 a share in the second quarter, up from 84 cents a year ago on a rise in sales to $2.306 billion from $1.747 billion. Net income was $214.7 million, up from $154 million.

First-half profit was $391.2 million ($2.16 a share) on sales of $4.382 billion compared with $283.5 million ($1.55) a year earlier on sales of $3,396 billion.

President P. F. Oreffice said Dow was prepared for a recession in the second half but so far hasn't seen convincing evidence that its business will be hurt. He said that Dow's basic chemical business has been good and that its oil and gas field service and plastic businesses also have done well.

American Airlines more than doubled its profit of a year ago in the three months ended in June because of a surge in passengers and a gain from the insurance coverage of its DC10 that crashed in Chicago May 25.

American said its passenger traffic rose 28.8 percent in the quarter despite the grounding of the McDonnell-Douglas DC10s in June following the nation's worst air disaster that claimed 273 linves.

The big passenger gains for American came in April and May when United Airlines, the nation's biggest $&(WORD ILLEGIBLE carrier, was idled by a strike. But American traffic was up 9.1 percent over the 1978 pace in June, even though United was flying again and DC10s were prohibited from operating.

American's net income for the second quarter was $95.3 million ($3.22 a sahre), up from $43.9 million ($1.43) a year ago.

The 1979 profit included an after-tax gain of $24.3 million (85 cents) on the excess of insurance proceeds over the book value of the wrecked DC10 resulting from the increased market value of the DC10 over the figure entered on the books when the aircraft was purchased. Tax credits added 29 cents a share.

Six-months profit was $88.4 million ($2.87) against $36.9 million ($1.08) a year earlier. The 1979 first-half results included 65 cents a share from tax credits and gains on the repurchase of subordinated debentures in addition to the excess insurance recovery.

Second-quarter revenues were $857.4 million against $688.2 million a year earlier, and first-half revenues were $1.53 billion, up from $1.28 billion.

Chairman Albert V. Casey said steadily rising fuel costs were a major contributor to the carrier's increased expenses.

Second-quarter net income for B.F. Goodrich Co. increased a record 41 percent over the 1978 quarter, sending net income from the first half of the year 54 percent above the previous year's level, the company reported yesterday.

Net income for the second quarter was $24.6 million ($1.46 a share) on sales of $753.1 million compared with net income of $17.4 million ($1.15) on sales of $670 million in the second quarter of 1978.

In the first half, net income was $50;9 million ($3.03) compared with $33.1 million ($2.19) in the first half of 1978.

John D. Ong, Goodrich chairman, credited chemical product sales for the record results.