Bethlehem Steel Corp. yesterday reported a $92 million first-quarter loss because of its troubled steel business, and U.S. Steel Corp. reported a $249 million loss because of falling oil prices.

Among other companies reporting earnings yesterday, Sperry Corp., Hershey Foods Corp. and Warner-Lambert Co. reported increased profits for their latest quarter, while Eastern Air Lines Inc. reported a $110.6 million loss.

Bethlehem Chairman Walter F. Williams told shareholders that a plastics subsidiary is being sold and other nonsteel assets will be sold to raise badly needed cash.

At U.S. Steel, the quarterly loss came on sales of $4.7 billion. The company earned $185 million (63 cents a share) on sales of $5 billion in the first quarter of 1985. Its oil and gas segment, including Texas Oil and Gas Corp., posted a $133 million operating loss before foreign taxes, compared with a $413 million profit a year ago.

Steel operations had operating income of $8 million on sales of $1.5 billion compared with income of $34 million on sales of $1.6 billion in the 1985 period.

Bethlehem said that sluggish prices for steel were keys to the continued financial loss.

The quarterly loss of $91.8 million on sales of $1.2 billion was the third in a row and 15th in the last 17 quarters. The company lost $62.1 million on sales of $1.2 billion a year earlier.

The company also said it agreed to sell its plastics and building products company, Kusan Inc., to the subsidiary's current managers for $163 million. The deal should generate a $50 million gain for Bethlehem.

*Eastern Air Lines Inc. yesterday announced a $110.6 million loss for the first quarter, blaming the drop on fare wars and uncertainty over a labor crisis. The losses compared with profits of $24.3 million (35 cents a share) in the first quarter of 1985. Revenue was $1.13 billion, down from $1.2 billion.

"Sharply lower revenue yield per passenger brought about by industrywide fare discounting, and consumer uncertainty over union strike threats contributed to a disappointing first quarter," said Frank Borman, Eastern's chairman.

*Sperry Corp. reported yesterday that its fourth-quarter net income rose by 8.9 percent, but profits fell sharply in the company's latest fiscal year.

Sperry said net income for the fourth quarter that ended March 31 was $115.3 million ($2.02 a share), up from $105.9 million ($1.89) a year earlier. Revenue was $1.8 billion, up from $1.59 billion.

For its entire 1986 fiscal year, Sperry reported net income of $46.8 million (82 cents), down from $286.7 million ($5.15) a year ago. Revenue rose to $5.74 billion from $4.97 billion in fiscal 1985.

The steep annual earnings decline stemmed chiefly from a $233.2 million after-tax loss from discontinued operations of the Sperry New Holland farm equipment unit, the company said. Sperry agreed to sell the division to Ford Motor Co.

Gerald G. Probst, Sperry chairman and chief executive, said that revenue and operating profit increases in commercial computer operations were offset partly by profit reductions stemming from a strike and production problems in Sperry's defense and aerospace operations.

*Hershey Foods Corp. reported record first-quarter profits of $27 million (86 cents a share), up from $22.7 million (73 cents) in the same period last year.

Sales rose to $508 million from $477 million, the company said.

Chairman Richard Zimmerman said a price increase and product introductions contributed to gains in sales and operating income at the corporation's Hershey Chocolate Co. unit.

*Warner-Lambert Co. said yesterday its first-quarter earnings rose 8.3 percent to $65 million, (87 cents a share) from $60 million (76 cents) a year ago.

Sales were $747 million, down from $795 million in 1985. The 1985 figure includes health technologies businesses that are being divested, company officials said.

Aided by the weaker dollar, the company's worldwide sales increased 9 percent over the first quarter of 1985, excluding businesses being divested, Chairman Joseph D. Williams said. Sales of prescription drugs rose 14 percent worldwide.