American Telephone & Telegraph Co. yesterday reported a drop of 7 cents a share in earnings for 1982, caused in part by a $317.6 million writedown on a decision to phase out Western Electric manufacturing operations at Kearny, N.J.

Also yesterday, Gulf Oil Corp., the fifth largest U.S. oil company, reported its fourth-quarter earnings dropped 25 percent, while No. 11 Sun Co. had a 1 percent gain in operating profits for the quarter and Standard Oil Co. (Ohio), the 13th largest, announced a 3 percent decline.

Xerox Corp. said it had a 29 percent drop in earnings for all of 1982 on a 1 percent drop in revenues.

AT&T's net income actually was up to $7.279 billion on revenues of $65.093 billion from $6.823 billion in 1981 on revenues of $58.066 billion.

But per share net dropped to $8.40 from $8.47 because there were 61 million more shares outstanding in 1982. The 1982 net included a gain of $352.7 million from the cumulative effect of an accounting change that deferred income tax payments. This offset most of the reserve on the Kearny phaseout.

The company did not announce fourth quarter calendar results, saying they are never announced simultanteously with the year's results.

In the fourth quarter, Gulf earned $226 million ($1.29), up from $301 million ($1.60) a year earlier. Revenues advanced 3 percent to $8.16 billion vs. $7.94 billion.

Gulf said gasoline prices tumbled 9 cents a gallon and heating oil prices 6 cents a gallon in the final 1982 quarter.

For the year, Gulf's earnings declined 27 percent to $900 million ($4.98), from $1.23 billion ($6.37) in 1981. Revenues rose fractionally to $30.6 billion from $30.4 billion.

Gulf's refining, marketing and chemical operations in the United States and abroad had losses of more than $300 million in 1982.

Sun said the 1 percent gain in its fourth-quarter operating profits reflected higher prices for its Canadian synthetic crude and stronger U.S. refining and marketing results.

But Sun's net profits dropped 69 percent to $151 million ($1.26), from $448 million ($3.70) in the 1981 fourth-quarter when the company had an after-tax gain of $299 million from major divestitures. Revenues were off 8.8 percent to $4.1 billion vs. $4.5 billion.

Sun's 1982 earnings fell 16 percent to $537 million [4.40], from operating income of $642 million ($5.13) before an after-tax gain of $434 million, equal to $3.46 a share, in 1981. Revenues were off less than 1 percent to $16.3 billion against $16.4 billion.

Sun said its 1982 earnings were hurt by depressed of crude oil prices and the sluggish economy that reduced natural gas sales. U.S. exploration and production profits also sagged.

Sohio's fourth-quarter earnings dipped to $463 million ($1.89), from $477.8 million ($1.94) a year earlier. Revenues were down 15 percent to $3.21 billion vs. $3.77 billion.

Sohio said the recession, higher exploration expenses and increased interest costs cut into fourth-quarter results.

In 1982 Sohio earned $1.87 billion, or $7.92 a share, down 3.4 percent from $1.94 billion [7.92] in 1981. Revenues fell 4.3 percent to $13.5 billion vs. $14.1 billion.

Sohio said all its businesses had lower earnings for 1982 except refining and marketing and coal, which had a major work stoppage in 1981.

On continuing operations, Xerox said net income was off 36 percent for the year and 46 percent for the quarter.

Chairman C. Peter McColough said a weak economy, lower pricing, adverse currency translations and heavy restructuring costs cut the earnings even though the market for copiers and duplicators remained active. Xerox reduced its working force by 9,500 during the year, 4,700 of them in the final quarter.

Net income for the year was $423.7 million ($5) on revenues of $8.456 billion compared with $598.2 million ($7.08) in 1981 on revenues of $8.51 billion.

For the final quarter, net income was $53.7 million (63 cents) on revenues of $2.211 billion compared with $112.7 million ($1.33) a year earlier on revenues of $2.235 billion. Fourth-quarter earnings were hit fairly hard by the devaluation of the Mexican peso.