G.M., hard hit by chip shortages, reports a 33 percent decline in quarterly sales.

General Motors said on Friday that its new-vehicle sales in the United States were down 33 percent in the third quarter from a year earlier as a result of semiconductor shortages and dwindling inventories on dealer lots.

The automaker sold 446,997 vehicles in the July-to-September quarter, a sharp decline from the year-ago period, when it sold 665,192 light trucks and cars. In the third quarter of 2019, G.M. sold 738,638 vehicles.

The global shortage of semiconductors has forced G.M. and other manufacturers to idle plants for weeks at a time, leaving dealers with tight stocks of cars and trucks for sale. At the end of September, G.M. had just 128,757 vehicles in dealer inventories, down from 211,974 at the end of the second quarter.

The company emphasized that customer demand was not the problem. “Underlying demand conditions remain strong, thanks to ample job openings, growing pent-up vehicle demand and excess savings accumulated by many households during the pandemic,” Elaine Buckberg, G.M.’s chief economist, said in a company statement.

And the company signaled that the chip supply situation was improving. “We look forward to a more stable operating environment through the fall,” said Steve Carlisle, executive vice president and president, G.M. North America.

G.M. dealers had more than 334,000 vehicles in stock at the end of the first quarter. In years past, G.M. often kept about 800,000 vehicles in dealer inventories.