DETROIT, Sept. 4 — Bigger discounts helped General Motors increase sales in August while Toyota, Ford Motor and Chrysler posted declines amid troubles in the credit and housing markets, according to figures released today.

G.M.’s sales rose 5.3 percent compared with those in the month a year earlier while Toyota’s sales were down 2.8 percent, a rare decline. It was the first time since October 2006 that G.M. widened its lead over Toyota.

“Reduced credit tied to the subprime squeeze challenged consumer confidence this month,” said Jim Lentz, executive vice president of Toyota Motor Sales.

Because of the unexpectedly difficult sales environment, G.M. said it planned to produce 10 percent fewer vehicles in the fourth quarter than it did in the period a year earlier. But Ford, whose sales were down 14 percent in August, said its fourth-quarter production would be slightly higher than it was in 2006.

Chrysler’s sales were down 6 percent; it did not disclose a fourth-quarter production target.

G.M. had a strong month in the full-size pickup segment after increasing discounts by an average of $400 a vehicle from July. Since June, when Toyota began rapidly introducing bigger discounts on its Tundra pickup, G.M. has increased incentives on the Chevrolet Silverado and G.M.C. Sierra by $1,000, the company’s chief sales analyst, Paul Ballew, said.

Pickup sales were up 32 percent at G.M. in August and up 69 percent at Toyota but down at both Ford and Chrysler.

Although G.M. has said it wants to rely less on discounts to sell vehicles, Mr. Ballew said the company could not afford to let Toyota and other competitors eat away at one of its most important vehicle segments.

“We’re going to defend that turf,” he said. “We need to for the overall health and position of our brands in the marketplace.”