The Big Three U.S. auto companies' combined profits in the second quarter of 1977 totaled $1.73 billion - highest for any three-month period in automotive history.

Ford Motor Co. yesterday said its profit of $530 million was 20 per cent higher than a year ago and set a record, while Chrysler Corp. came in yesterday with earnings of $103.8 million, down 33 per cent, largerly as the result of a six-week truck assemble plant strike.

But it was industry giant General Motors Corp. earnings of $1.1 billion in the April-June quarter that pushed the industry to a record. The previous high of $1.5 billion was set the second quarter last year. GM reported its results Wednesday.

Chrysler chairman John Riccardo and president Eugene A. Cafiero, echoing a GM statement of industry shutdowns if there is no new clean air law, said Congress now appears to be making a "good-faith effort" to produce a sensible law "in time for us to begin an orderly production of 1978 cars . . . However, a delay in establishing new standards would have serious consequences for the automobile industry, its suppliers and employees," they said.

Chrysler earnings of $1.72 a share came on record dollar sales of $4.4 billion. A year earlier, the company earned $155.1 million ($2.58 a share) on sales of $4.1 billion. This year's profit included an extraordinary credit of $13.2 million for income taxes compared with a $30 million credit last year.

Ford said its profits, dollar sales, factory sales and payroll were at record levels in the second quarter of 1977.

But Ford chairman Henry Ford II. whose company has indicated a price increase as high as 6 per cent, or $398 on the average 1978-model car, complained that profits from U.S. and Canadian operations were hurt by the firm's inability to recover all of its cost increases.

Ford said its profit came on record sales of $9.7 billion, up 22 per cent from $8 billion last year when profits amounted to $442 million. Its previous quarterly high was the $483 million profit turned in during the first three months of 1977.

Earnings amounted to $4.49 a share compared with $3.76 in the second quarter of 1976. The per-share earnings figure takes into account a five-for-four stock split in May.

Like GM, Ford sought to minimize the size of its profits, saying the aftertax return on sales declined to 5.5 per cent in the quarter from 5.7 per cent a year ago. The drop was attributed to lower profit margins in the North American operations.

Earnings from operations outside the United States and Canada rose 43 per cent to S179 million, or 34 per cent of the total profit compared with 28 per cent last year.

"The profit improvement outside the United States and Canada largely reflected higher unit volumes," the Ford chief executive said. "In North Amercian operations, gains resulting from higher volumes and operating efficiencies were offset to a substantial degree by failure to recover cost increases through pricing."

LTV Corp. yesterday posted a first-half loss and noted a sharp decline in second-quarter profits, blaming poor showings by its Jones & Laughlin steel and Wilson foods subsidiaries.

For the half, the Dallas-based conglomerate said its lost S2 million against net income of S16.3 million (S1.35 a share) a year ago. First-half sales rose from $2.3 billion to $2.34 billion. In the second quarter. LTV earned $1.6 million (7 cents) against 1976's $9.4 million (79 cents). Sales rose from $1.18 billion to $1.22 billion.

In addition to a poor showing by the foods subsidiary, LTV said, "price increases in steel operations came too late to offset rising costs, including higher labor costs that became effective May 1 . . . under the agreement reached . . . with the United Steel-workers of America."

Standard Oil Co. of Ohio, the nation's 19th largest petroleum producer, yesterday said its second-quarter net income rose 52 per cent over last year's second-quarter results on a 12 per cent gain in sales.

Sales of a gas-producing propoerty and some service stations, along with improved domestic petroleum operations more than offset higher interest costs and slightly lower coal, chemical and plastics earnings, Sohio said.

Net income in the latest period was $55.7 million ($1.44 share) on sales of $824.1 million compared with 1976 second-quarter net income of $36.6 million (95 cents) on sales of $735.6 million.

The 1976 earnings figure were restated to account for the disposition of FMC's fiber division, most of the assets of its pump division and its 50 per cent interest in a pump company.

For the first half, FMC reported net income of $69.4 million ($2.08), up 9 per cent from the restated 1976 results of $63.8 million ($1.92).