General Motors Corp., which saw sales slide 12.5% in March, says a parts shortage due to a prolonged strike at American Axle Mfg. & Holdings Inc. has not affected retail deliveries and should not impact April results.

“(The strike) has not affected retail one bit,” says Mark LaNeve, vice president-GM North American vehicle sales, service and marketing.

According to Ward’s data, GM sold 280,834 new passenger cars and light trucks in March, compared with 315,966 in like-2007.

The auto maker chooses to blame the decline on waning consumer confidence, rather than a parts shortage that has idled or slowed production at 29 GM manufacturing sites.

Nearly all the production loss, nearly 100,000 units, has been fullsize trucks, and the auto maker has welcomed the inventory draw down.

However, GM last week added to the list of its parts-strapped facilities a passenger-car plant in Hamtramck, MI, that builds the slow-selling Cadillac DTS and Buick Lucerne fullsize sedans.

Media reports suggest GM’s compact car plant in Lordstown, OH, will see an altered production schedule as soon as this week, while a factory in Orion Twp., MI, that builds the hot-selling Chevrolet Malibu also could be facing a parts shortage.

Even with the help of Malibu production at a second plant in Fairfax, KS, since the car’s launch in October, GM has not been able to meet consumer and dealer demand for the extensively redesigned midsize sedan.

LaNeve declines to comment specifically on the Malibu, saying only GM’s retail share remains well insulated from the work stoppage at AAM, its key driveline and chassis-components supplier.

“We’re monitoring the situation very closely,” he says. “We haven’t seen a retail sales impact so far. We believe we’re in good shape, and beyond that there’s no benefit to me commenting,” LaNeve says during a monthly sales call with analysts and journalists.

“It’s not a GM situation,” he insists. “It affects us, but we’re not the two critical parties here.”

AAM said today it has provided the United Auto Workers union, which ordered 3,650 workers to walk off the job at plants in Michigan and New York five weeks ago, with information the union says it needs to effectively evaluate the company’s cost structure.

The information was shared with the UAW after both parties signed a confidentiality agreement, the supplier says.

AAM Founder, Chairman and CEO Richard Dauch reiterates his hope of reaching an agreement that will make the supplier more competitive without moving work elsewhere. Last week, Dauch hinted work could go overseas if a labor agreement could not be reached.

“Establishing a market-cost, competitive labor agreement with the UAW that recognizes AAM as a Tier 1, Tier 2 and Tier 3 supplier to the automotive industry is critical to providing a viable, profitable and sustainable future for the company and its UAW-represented associates at the original U.S. locations,” Dauch says in a statement today.

While truck inventories remain high, GM runs the risk that certain trim levels could become unavailable or certain regions where demand is greater might feel an availability pinch, analysts say.

“We don’t have a problem now, and we’ve been working on being able to operate with tighter inventories,” LaNeve says. “We think we’re in good in shape.”

GM says its retail share in March hit 21%, the same as the first quarter and the level at which the auto maker has run the last two years. “We continue to see stability in our retail share,” says Mike DiGiovanni, GM’s director of global market and industry analysis.

Sales drivers for the auto maker in March included the Malibu, which saw a 7% gain to 15,082 units, and the Chevy Impala midsize sedan, up 9.6% to 29,010, according to Ward’s data. Sales of the redesigned Cadillac CTS luxury sports sedan improved 33.4% to 6,045 units.

LaNeve says the new Malibu now commands an average transaction price $4,000 higher than its predecessor, while the popular CTS sells for an average $7,000 higher.

GM’s midsize cross/utility vehicles also fared well in March. The all-new Buick Enclave, GMC Acadia and Saturn Outlook accounted for 14,312 deliveries.

“We’re looking forward to adding the Chevy Traverse to that growing segment by the end of the year,” LaNeve says.

At the same time, the sales chief admits consumer confidence continues to cut into overall volume sales, especially in fullsize pickups and SUVs. Sales of the auto maker’s bread-and-butter Chevy Silverado pickup fell 17.6% to 42,561 units in March, while Chevy Tahoe sales tumbled 29% to 9,772.

“It is a very soft traditional truck market out there,” LaNeve says. “Fullsize pickups, utilities, truck-based SUVs were all soft, reflecting an overall weakness in the economy.”