The General Motors Co. board of directors accepts President and CEO Fritz Henderson’s resignation at its regular monthly meeting Tuesday, leaving the auto maker’s leadership in limbo and questions swirling behind the decision’s motivation.

Ed Whitacre, hired by President Obama as chairman of GM in a purge of the auto maker’s former board of directors after it exited bankruptcy, will add the role of CEO while the search for Henderson’s long-term replacement begins immediately.

GM Vice Chairman Bob Lutz will remain with GM, officials say, and deliver a keynote address, in place of Henderson, to open the Los Angeles auto show Wednesday.

Whitacre hosted a hastily called, 12-minute press conference late Tuesday to announce Henderson’s resignation but gave little reason behind the decision.

“Fritz has done a remarkable job leading the company through an unprecedented period of challenges and change, and momentum has been building in our company over the last several months,” says Whitacre, known for merging communications giants Southwestern Bell Corp. and AT&T Inc. but arguably bringing little auto industry experience to GM at the time of his appointment.

“But we all agreed that some change needed to be made going forward,” the 68-year-old says.

Whitacre, who will shift from his native Texas to working at GM world headquarters in Detroit on a daily basis, is GM’s third CEO in the last six months.

Henderson, 50, spent 246 days atop one the world’s industrial icons, installed by the government’s auto task after the Obama Admin. forced out Chairman and CEO Rick Wagoner.

Chris Preuss, head of GM communications, responded to journalists seeking further clarification behind Henderson’s ouster by saying, “Based on the determination of the board and the pace of change in the company, it was determined that it was best to initiate a change of direction.”

The pace of change at GM has been seen as moving quickly, although not entirely smoothly. The auto maker posted a $1.2 billion loss in its first financial report out of bankruptcy, but the outcome beat expectations and cash flow was seen as strong.

GM also announced plans to pay back some taxpayer loans early.

GM has a number of product hits in the market, including the Chevy Equinox cross/utility vehicle and Camaro sports coupe.

But after eight months of negotiations to sell its Adam Opel AG unit to Canadian parts supplier Magna International Inc., GM reversed course at the 11th hour and chose to restructure the German auto maker itself.

In addition, GM has seen deals to sell its Saab and Saturn divisions fall apart in recent weeks, and Henderson and the board appeared to differ on a plan for GM to go public in the second half of 2010.

Whitacre recently doused Henderson’s enthusiasm over an IPO after reports of the timetable surfaced.

Whitacre tells journalists today the auto maker will open up with details of Henderson’s departure in the coming days, calling future executive availability in exchange for patience from the media “a fair deal.”