The nation's No. 1 steel producer, U.S. Steel Corp. reported third quarter earnings and sales fell, although sales and profits increased for the nine months.

Income for the third quarter was $81.3 million (94 cents a share) on sales of $3.2 billion, compared with income of $88.8 million ($1.04) on sales of $2.8 billion for the third quarter of 1978.

The first nine months' earnings were $268.7 million ($3.13) sales of $9.9 billion, the company said, compared with $147.4 million ($1.74) on sales of $8.1 million last year.

U.S. Steel officials laid the quarter's decline to lower steel shipments, the ravages of inflation and higher imports.

U.S. Steel officials noted that steel imports, which declined in the first nine months of the year, rose in July and August.

"The July-August level, an annual rate of approximately 20 million tons, is approaching the record 1978 level," officials said. "Many of these imports are being dumped here at prices that violate existing U.S. trade laws. At a time when demand for steel in the United States is declining, such imports are damaging to the domestic steel industry and the jobs of its employes."

Sales at Warner-Lambert Co. increased in the third quarter and net income declined, mainly due to the establishment of a reserve in connection with the consolidation of the company's pharmaceutical operations, the firm said yesterday.

Third quarter sales rose to $817 million from $730 million in the third quarter of last year. Net income was $4.7 million (6 cents) compared with $60.8 million (76 cents) in the third quarter of 1978.

Sales for the first nine months of the year rose to $2.4 billion from $2.1 billion in the same period last year. Net income for the first nine months was $123 million ($1.54) compared with $168 million ($2.11) a share in 1978.

Kerr-McGee Corp., the energy firm, earned $1.64 a share in the third quarter, up from $1.32 a year ago, on a rise in sales to $679.8 million from $523.57 million.

Net income climbed to $42.59 million from $34.18 million.

Nine months profit was $119.62 million ($4.62) on sales of $1.928 billion compared with $78.17 million ($3.02) a year ago on sales of $1.529 billion.

Borden Inc., the food and chemical combine had an 8.8 percent gain in earnings for the third quarter to $1.22 a share from $1.12 a year ago on a 16.3 percent rise in sales. Net income was $38.02 million of sales of $1.094 billion compared with $34.94 million a year ago on sales of $941.2 million.

Nine months profit was $102.45 million or $3.30 a share, level with the $102.84 million a year earlier but sales rose to $3.166 billion from $2.803 billion.

Chariman Eugene J. Sullivan said higher interest costs, decline in the foods division's business and increase in foreign currency translation losses, plus lower income from bakery and confectionery caused the flat earnings for nine months.

The Liggett Group has reported increased sales and earnings for the third quarter despite a drop in the sales of cigarettes.

Net earnings for the Liggett Group were $27.1 million ($3.17) for the quarter ended Sept. 30. Net earnings for the third quarter of 1978 were $13.8 million ($1.53).

Sales for the third quarter this year were $296 million compared with sales of $247 million for the third quarter last year.

Despite the lower sales of cigarettes the company said its earning income from cigarettes was higher "because of lower promotional expenditures." The company did not release figures on cigarette sales.

Times Mirror Co. reported third-quarter earnings yesterday of $42.5 million ($1.25) up from $3.13 million (91 cents) in the third quarter of 1978.

Revenues for the 12-week quarter ended Oct. 7 were $410.8 million, Times Mirror Chairman Franklin Muphy said, up from $352 million in the prior year.

Earnings for the first three quarters were $109.4 million ($3.22) up from $94.6 million ($2.73) in the first three quarters of 1978. Revenues for the 40 weeks ended Oct. 7 were $1.2 billion, the company said, up from $1.06 billion a year ago.

Consolidated Rail Corp., suffering from declining shipments of autos and auto parts, reported a third quarter loss of $40 million yesterday, compared to a 1978 third-quarter loss of $48.5 million.

For the nine months, Conrail lost $138.3 million, compared to a $325.4 million loss for the 1978 period, an improvement of $187.1 millon, the company reported.

Conrail said its total costs in 1979 were $1,023 billion, compared to $953.4 million in the third quarter. For the nine months, Conrail's costs were $3.061 billion, compared to $2.095 billion in 1978.