General Motors executives say inventories of the Chevrolet Volt, a car the auto maker hopes will remake its post-bankruptcy image into a producer of environmentally friendly vehicles, will not hit levels capable of satisfying demand until second-quarter 2012.

Sales of the extended-range electric vehicle bounced back in August with 302 units.

Deliveries dipped in July to 125, according to WardsAuto data, prompting critics to decry slumping demand for the 9-month-old model.

The car has averaged close to 400 sales a month so far this year.

GM’s overall sales in August rose 13.5% to 218,479 units from 185,113 in like-2010. The industry saw 26 selling days in the month, one more than year-ago.

GM officials blamed the Volt’s swoon last month on limited availability due to a multi-week, ’12 model retooling shutdown at the Detroit-Hamtramck assembly plant between June and July.

The auto maker also cited a pullback in national advertising for the Volt, which coincided with the plant’s shutdown, as well as stocking dealer lots with demonstration models in the seven states and 550 dealerships where it is available. Later this year, the car’s availability goes nationwide to some 2,600 Chevy dealers.

Volt stocks are rising again, up to 1,361 units today from 226 at the end of July, WardsAuto data shows.

Don Johnson, GM’s U.S. sales chief, says between 700 and 800 Volts are meant for demonstration purposes. Dealers must stock a demonstration model before receiving salable units, so retail sales of the car probably will not jump any time soon.

“It will affect retail stock,” he tells WardsAuto in a conference call today with journalists and Wall Street analysts to discuss GM’s August sales. “It’s going to take us a month or two to really fill up the retail inventory for those dealers.”

Johnson expects Volt inventories to reach levels capable of meeting demand around the second quarter of 2012. GM has delivered 3,172 Volts to date. The auto maker expects to produce 16,000 units this year and 60,000 in 2012, with 45,000 dedicated to the U.S.

Alan Batey, head of U.S. sales for Chevrolet, says it’s too early to determine if the Volt is paying the image dividends GM hoped for, but it does a draw a crowd. “It’s a magnet at grass-root events and displays,” he says, admitting, “It’s a bit early to draw any conclusions.”

Eleven different GM models set 2011 monthly sales records last month, including the GMC Terrain cross/utility vehicle with 7,875 deliveries and the Chevy Silverado fullsize pickup with 36,832. The Silverado enjoyed its best month since December 2010.

The Chevy Tahoe and Suburban, GMC Yukon and Yukon XL, Chevy Avalanche and Cadillac Escalade EXT also set new monthly marks for the year.

Johnson says buyers of the large trucks are feeling more confident since gasoline prices stabilized, although some seasonality may have played a role with winter approaching.

Incentives for the auto maker rose by less than $100 in August, Johnson says. The average transaction price for a GM vehicle grew by $200, compared with July, but fell “slightly” against like-2010 on the shift to higher car sales overall.

GM closed August with a dealer inventory of 556,884 units, about 19,000 vehicles higher than July, and at a 66 days’ supply.

Fullsize pickup inventories, which the auto maker wants to trim in the coming weeks with production adjustments, stood at 212,520 units from some 215,720 in July, for a 107 day’s supply.

“We’re being very prudent when it comes to managing our inventory,” Johnson says, adding the auto maker remains on track to achieve its year-end pickup-inventory goals.

“The trends we forecasted are playing out,” he says, “albeit in an industry that’s not growing quite as quickly as we expected.”

jamend@wardsauto.com