Continuing uncertainties over fuel supplies this summer helped to reduce early-June car sales by nearly 30 percent, the Big Three U.S. automakers said today.

General Motors Corp., Ford Motor Co. and Chrysler Corp. reported combined sales of 171,965 units in the first 10 days of the month compared with 275,427 units a year ago.

Truck sales, which had been going strong before the latest onset of gasoline shortages, plummeted 37.9 percent on total deliveries of 55,685 units in early June.

The industry's sales rate of 22,616 cars a day was the third lowest in the past 11 years and the lowest since the dark days of the 1974-75 recession. Sales in early June in those years were a little over 21,000 a day and under 20,000 a day.

The decline in the rate of sales from the last 10 days of May was startling, partly the result of seasonal buying patterns. Sales always fall from May to June.

Sales in the final third of May were running at 20,023 a day. In early June, they were down 42 percent.

In the previous eight years, the average decline from late May to early June was 26 percent.

Ford posted the greatest drop during the period with sales of 47,277 passenger cars - a 31.4 percent decline from last year's record pace.

GM sales of 102,946 cars were 29.3 percent below levels of a year ago despite continued strong sales of its new X body compacts which surpassed the 100,000 mark for the year during the period.

Chrysler reported sales of 21,742 cars, a 28.3 percent decline from a year ago.

American Motor Corp., which no longer reports 10-day sales, was estimated by industry analysts to have sold 5,100 units, a 26.9 percent fall-off. Volkswagen of America reported sales of 3,866 U.S.-built Rabbit sub-compacts, but it was not selling them at the same time last year.

Combined sales of all five major producers were estimated at 180,931 units, 28 percent less than a year ago.

GM Vice President Robert D. Burger said the sales declines reflected continuing concerns of U.S. car buyers over "the current energy situation," which have pulled the rug out from under the domestic car market for the past two months.

Burger said that GM, the No. 1 automaker, expects car sales "will return to their normal pattern when the uncertainty passes."

However, Ford Vice President Gordon B. Mackenzie voiced a different view.

"The confusion and emotionalism about fuel supplies is lessening," Mackenzie said. "We have not seen - and do not expect to see - any immediate sales reaction as market movements lag changes in consumer attitudes. We do, however, expect to see a gain in mid-size and larger-car mix in the second half of the year," he said.