U.S. Steel Corp.'s fortunes turned around in 1984, allowing it to post a profit of $493 million for the year, compared with a loss of $1.16 billion in 1983, as sales for the nation's largest steel producer rose to $19.1 billion from $7.5 billion.

Among other major companies reporting results yesterday, Texaco Inc. said it lost $552 million in the fourth quarter, Chevron Corp.'s 1984 profits dropped by 4 percent and Pacific Telesis Group's first-year profits were $828 million on revenue of $7.8 billion.

U.S. Steel had fourth-quarter net income of $29 million, but a small loss after payments for dividends on preferred stock compared with a year-earlier loss of $983 million. Sales declined to $4.65 billion from $4.71 billion a year before.

U.S. Steel said each of its business segments posted a pretax operating profit in 1984 and had better results than in 1983. Steel and related resources had operating income of $142 million on sales of $6.5 billion last year compared with a 1983 loss of $610 million on sales of $5.9 billion.

The company said the turnaround was mostly the result of cost-reduction programs, the effect of lower pension costs, increased net steel selling prices, an improved mix of steel products shipped, and higher operating and shipment levels. Steel shipments for the year rose to 11.8 million tons from 11.0 million in 1983.

The Marathon Oil Corp. subsidiary's pretax operating income rose to $1.27 billion from $1.13 billion, while sales increased to $10.2 billion from $9.3 billion.

* Texaco Inc., the nation's third-largest oil company, said its setback was caused by a more pessimistic assessment of the value of its oil-producing assets.

Texaco said the large loss compared with a profit of $256 million ($1 a share) a year earlier. Revenue rose 16.2 percent to $12.2 billion from $10.5 billion.

The loss was a result of a $765 million write-down of assets, which had been announced in November. The new assets refer to Getty Oil Co., which Texaco bought last year for $10.1 billion.

Without the write-down, earnings in the fourth quarter would have been $213 million (82 cents), still a 16.8 percent drop from a year earlier.

For all of 1984, earnings fell 75.2 percent to $306 million ($1.03) from $1.23 billion ($4.80). Without the write-down, annual profit would have been down 13.1 percent at $1.07 billion ($4.22). Revenue rose 17 percent to $48.1 billion from $41.1 billion.

* Chevron Corp., the fourth-largest oil company, said its fourth-quarter profit increased to $434 million ($1.26 a share) from $403 million ($1.18) a year earlier. Revenue fell 5.4 percent to $7 billion from $7.4 billion.

Chevron spent a record $13.3 billion in 1984 to buy Gulf Corp. In 1984, the company also changed its name to Chevron from Standard Oil Co. of California.

For all of last year, earnings slipped 3.5 percent to $1.53 billion ($4.48) from $1.59 billion ($4.65). Revenue held steady at $29.2 billion.

George M. Keller, the chairman of Chevron, said that if crude oil prices continue to fall, earnings from oil production will suffer. Earnings from refined petroleum products already have been hurt.

* Pacific Telesis Group reported $828.5 million in earnings on $7.8 billion in revenue for 1984, its first year of operation since the breakup of the nationwide AT&T system.

"I beleve that we have definitely answered all those questions raised in the months before divesture about Pacific's financial and technological capabilities to compete outside the Bell umbrella," said Chairman Donald E. Guinn.

"Stringent cost control and an aggressive marketing effort combined to produce a substantial return on our shareowners' investment," he said. "Our return on equity was 13.2 percent in 1984, up from 10 percent for Pacific Telephone at the end of 1983." Pacific Telesis stockholders earned $8.46 a share for the year.

For the fourth quarter, the communications company, which serves customers in California and Nevada, had revenue of just under $2 billion and earnings of $201 million ($2.01 a share).