DETROIT – Audi AG has an ambitious $15-billion investment slated for the next five years, with 70% earmarked for new product.

One item the auto maker may be cutting from its investment plan, however, is manual transmissions for the U.S.

Audi officials, at a roundtable discussion with the media at this week’s North American International Auto Show here, admit they’re considering doing away with the stick shift for its mainstream U.S. models.

“It’s conceivable in the U.S. we may dispense with manuals,” Johan de Nysschen, executive vice president of Audi of America Inc., says.

Manual-transmission installation rates in the U.S. continue to fall. And despite ongoing efforts to reinforce the brand’s sporty characteristics, Audi cannot ignore the reality that most U.S. customers – as opposed to Europeans – simply do not want to deal with a clutch pedal, de Nysschen says.

“For us, the S-Tronic represents the best of both worlds,” he says, referring to Audi’s version of parent Volkswagen Group’s successful automated manual transmission, named Direct Shift Gearbox.

The S-Tronic is a dual-clutch manual transmission fitted with an electrohydraulic module that automatically actuates the clutch. The high-tech transmission can shift gears on its own, just like an automatic transmission, or allows the driver to shift gears sequentially, without a clutch pedal.

De Nysschen stresses that Audi’s high-performance S and RS variants of its mainstream models would continue with manual transmissions, because those buyers typically seek the full control of a manual transmission and clutch pedal. Audi currently has S or RS variants of almost all its standard model lines except the Q7 cross/utility vehicle.

“I would not imagine an automatic-transmission RS4 (for example),” de Nysschen says, adding, “The mainstream cars (in the U.S.) may well go automatic only.”

He says Audi expects to further expand use of the dual-clutch S-Tronic gearbox to replace both manual and conventional torque-converter automatic transmissions.

Audi interim CEO and CFO Rupert Stadler says the auto maker plans to increase its product range from 22 models today to 40 models during the next five years of its ambitious investment plan. Much of it is focused on the U.S. market, where Audi had a record sales year in 2006, retailing 90,116 vehicles, an increase of 8.5%.

While the U.S. is Audi’s leading export market, trailing only Germany in sales, China rapidly is approaching U.S. volumes and soon may surpass the U.S. to become the auto maker’s largest export market, Ralph Weyler, board member for sales and marketing, says.

Despite a growth plan that earmarks a leap from 2006’s 905,100 worldwide sales to 1.4 million by 2015, Stadler says there are no plans to add manufacturing capacity until sales surpass 1 million units.

Then, he says, Audi likely first will look for capacity within the VW Group. Despite frequent auto industry discussion about the effects of currency exchange rates, all three Audi executives say the company currently is not considering the U.S. for a new assembly plant.

A factory in the U.S. “would not solve problems with the exchange rate,” Stadler says. “The time is not right.”