General Motors Corp. light-vehicle deliveries plunged 33.2% in April, but the auto maker sees a double-digit sales increase, compared with March and predicts signs of growing pent-up demand.

GM delivered 172,198 new vehicles in the month, compared with 257,782 year-ago, according to Ward’s data.

However, deliveries rose 11% compared with last month, building on an increase between February and March. And sales executives say consumers are slowly shifting into a buying mood again.

“We are seeing stability in the overall industry,” says Mike DiGiovanni, GM’s chief sales analyst.

DiGiovanni says positive economic indicators, such as rising consumer confidence, growing household income levels and cheaper gasoline, suggest consumers are poised to start spending again.

“They’ve got a pile of dollars,” he says during a monthly conference call with journalists and Wall Street analysts. “When they start to see gains in the economy, this money could hit the streets.”

DiGiovanni also cites newly released information from R.L. Polk & Co. showing one in six consumers plan to buy a new vehicle in the next two years. “Bottom line: consumers are poised to jump back in again,” he says.

But bankruptcy talk in the auto industry, as well as an effort by households to boost their savings, still have consumers taking “a wait-and-see” attitude, DiGiovanni admits. He reiterates the need for new-car sales incentives, which boosted deliveries in countries such as Germany and China again last month. Congress is debating a cash-for-clunkers incentive.

“The last missing link is this auto-sales stimulus package,” he says. “If it strategically comes right now, it is going to be the optimal time to see a really sharp, at least near-term, increase in sales because all of the elements are there.”

In the meantime, GM continues to struggle alongside the broader industry. The auto maker’s April retail sales fell 45% vs. like-2008 and it took 62,000 fleet deliveries to keep GM on pace with sales results by other auto makers.

However, GM did book gains at its four core brands, as Chevrolet, Cadillac, Buick and GMC sales rose 10% vs. March.

The auto maker plans to focus on those brands as part of its restructuring, while selling off or winding down the Hummer, Saab, Saturn and Pontiac divisions. Sales at those four brands are down 53% so far this year, a reflection of how their status has deteriorated in consumers’ eyes.

According to Ward’s data, Hummer sales in April plummeted 61.6%, Saab sales were off 9%, Saturn sales plunged 53.7%, and Pontiac deliveries dropped 36.7%.

GM also further backed off its incentives in the month, trimming that expense to an average of $3,775 per vehicle, or down $1,000 from March and $210 from like-2008. Third-party numbers confirm the tightening. Industry wide, incentive spending fell roughly $300, GM says.

GM Inventories shrank, as well, falling to 742,000 cars and trucks, down 82,000 units from year-ago.

Mark LaNeve, vice president-sales, service and marketing at GM North America, says GM dealers continue to make sales despite a flood of bad news surrounding the auto maker. In addition to drawing $15.4 billion in taxpayer loans since January and struggling to right-size its business by June 1 to avoid bankruptcy, rumors surfaced in April the auto maker might kill its Buick and GMC brands.

GM announced Monday it would end Pontiac production in 2010.

“Over the course of the monthm, we fought rumors that GMC was going away, Buick was going away, GM was going away…I saw everything but a Martian going to run General Motors,” he says. “We’ve been fighting these rumors, and none of them have helped sales. It’s almost become a way of life.”