Exxon Corp. reported a 15 percent drop in third-quarter income as foreign currency adjustments due to a weak dollar continued to play havoc with the income statements of the world's largest oil company.

[Other major oil producers announcing their latest earnings yesterday included Gulf, Atlantic Richfield, Standard of Indiana and Occidental Petroleum].

Exxon's net income declined 15 percent to $635 million ($1.42 a share) on a 10 percent increase in total revenues to $15.9 billion.

But on an operating basis, prior to currency adjustments and the inclusion of other nonoperating items, Exxon earnings totaled $807 million in the third quarter, an increase of 9.5 percent over a year ago.

The improved operating results were attributed to higher earnings from U.S. petroleum and natural gas production - mainly from the Alaskan North Slope - and to higher domestic prices for both natural gas and crude oil.

For the first nine months of 1978, Exxon net income was $1.92 billion ($4.30), up to 3.5 percent from the same period last year. Revenues rose to $46.7 billion in the period, a gain of 9 percent.

On an operating basis, Exxon earned $2.4 billion for the three quarters, gain of 9.5 percent.

Commenting on the earnings, Exxon Chairman Clifton Garvin Jr. said "caution is suggested in using net income results reflecting the foreign exchange effects, whether favorable or unfavorable, in assessing the corporation's ongoing performance and prospects for future growth."

And, as other oil company officials have done, he urged "changes in current accounting requirements under which these foreign exchange effects must be reported."

For the first nine months of 1978, net currency losses totaled $228 million, with $178 million occurring in the third quarter alone.

An earnings increase of nearly 7 percent was reported by the 5th largest oil producer, Gulf Oil Corp., while No. 6, Standard Oil Of Indiana gained 4.8 percent, and No. 7, Atlantic Richfield, had a 13.7 percent earnings gain.

Standard of Indiana, which uses the name Amoco, said its net earnings improved to $286.5 million ($1.96 a share) from $273.3 million ($1.86) in the third quarter of 1977. Revenue in the comparison periods was $4.2 billion and $3.5 billion.

For the first nine months of the year, net earnings hit $821.7 million ($5.62) on revenue of $12 billion compared with 1977 ninth-month earnings of $794.8 million ($5.42) and revenue of $10.4 billion.

Atlantic Richfield said net earnings totaled $20.5 million ($1.81 a share) on revenues of $3.4 billion in the third quarter. That was up from 1977 third-quarter earnings of $193.9 million ($1.59) on revenue of $2.8 billion.

For the first nine months, Atlantic Richfield said net earnings were $581.7 million $4.78) on revenue of $9.46 billion against 1977's $530.3 million ($4.36) on sales of $8.46 billion.

Gulf Oil Corp. reported third-quarter net income of $208 million on revenue of $5.08 billion compared with $195 million in profits on revenue of $5.05 billion for the 1977 third quarter. Per-share earnings were $1.07 compared with $1.00.

Nine-month's earnings were 538 million ($2.76 a share) compared with $577 millio or ($2.96) in 1977. Revenue was $14.68 billion this year and last year, Gulf said.

National Steel Corp., the nation's third largest steel maker, reported yesterday that near-record production caused third-quarter earnings to rise 197 percent.

National earned $40.4 million ($2.10 share) in the third quarter compared with $13.6 million (71 cents) last year. Sales for the quarter totaled $965.7 million compared with $820.4 million in 1977.

Nine-month earnings were $74.3 million ($3.87) compared with $43.7 million ($2.27) in 1977. Sales for the nine months were $2.74 billion, versus $2.42 billion in 1977.

Both Pan American World Airways and Texas International Airlines, the two airlines trying to take over National Airlines, yesterday reported that earnings in the third quarter were the best of any quarter in both companies' history.

Pan Am, buoyed by the surge in air passenger traffic brought on by discount fares, announced that third-quarter profits saored 54.3 percent to a record $101.3 million. The fourth largest American air carrier also said operating revenues reached a record during the quarter, rising 19.5 percent from the same period last year to $672.3 million.

The third quarter earnings equalled $2.01 a share compared with $65.6 million ($1.55 a share) in the same period last year.

For the first nine months, Pan Am said earnings were a record $123.4 million ($2.71), up 126.9 percent from the $54.5 million ($1.29) recorded in the same period last year.

Texas International reported record third-quarter earnings of $4.3 million (65 cents) compared with $2.9 million (53 cents) during the third quarter of 1977. Net income for thefirst nine months was $10.6 million ($1.80) compared with $4.7 million (88 cents) in the first nine months of 1977.

TXI President Frank Loremno said the good third-quarter earnings performance resulted from favorable economic conditions, the stimulative impact of their reduced-rate "peanuts" fares and continued success at productivity improvement.