The 4 percent gain in sales was below the 10 percent rise forecast by sales tracker Edmunds.com. And the gain was due mostly to the comparison to weak August 2005 sales, after GM's June and July sales got a big lift from its popular "employee pricing" incentive.

GM did see about the same gain in sales in both its car and its truck models. And the company said its retail sales, which excludes fleet sales to businesses, rose 8 percent in August.

GM also said it would cut its North American production target in North America by 12 percent, or 150,000 units. It said the reduction comes as it ramps up assembly lines for new versions of its full-size pickups and an ongoing reduction in sales to rental car companies, rather than any reduced sales outlook.