By Ben Klayman

DETROIT (Reuters) - General Motors Co <GM.N> finance chief Chris Liddell, who was passed over for the top job at the automaker last year, resigned suddenly on Thursday, renewing concerns about the automaker's stability at the top.

Liddell, 52, who joined GM last year from Microsoft Corp <MSFT.O>, will leave on April 1, the company said.

Liddell saw GM through its record $23 billion IPO last November after the company emerged from a government-sponsored bankruptcy. Replacing him is former Morgan Stanley <MS.N> banker Dan Ammann, who is now GM's finance vice president and treasurer. GM's board was apprised of the change this week.

Liddell's sudden departure reopened questions about GM's top leadership that many analysts had credited the automaker with having resolved since its IPO.

The company has had four chief executives in the last two years. Ammann will be the fourth CFO in the last three.

"Investors want to see stability in the management," said Josef Schuster, founder of iPox Schuster, a fund that specializes in investing in newly public companies, including GM. "From GM, you just don't see that."

GM's financial management and accounting systems had been singled out for criticism by the Obama administration's autos task force as a contributing factor in the company's 2009 collapse.

But Liddell had been credited with tightening controls on accounting and bringing a new commitment to paying down debt and pension shortfalls in order to build a "fortress balance sheet" that would protect GM during the next downturn.

"While the old GM culture needed to be fixed, the recent high turnover indicates that the new GM management team is still integrating," Barclays Capital analyst Brian Johnson said in a note for clients.

The change in the CFO position follows several other recent changes or promotions in GM's senior management team, allowing Chief Executive Officer Dan Akerson to put his stamp on the automaker.

"We have tried to reconfigure the focus of the company," he said, when asked on a conference call about the turnover.

Liddell's exit also clears the road to the top for Mark Reuss, whom insiders see as a potential successor to Akerson.

The 47-year-old Reuss, who has spent his career at GM and was promoted to North American president by then-CEO Ed Whitacre, is known as a "car guy" and frank speaker who has been critical of the way GM management focused on financial aspects over the quality of its vehicles before its restructuring.

Last month, GM posted a full-year profit that was its first since 2004 and its largest since 1999, but its shares fell below the IPO price as investor concerns shifted to rising oil prices and the higher costs of launching and selling new cars.

The IPO was needed to allow GM to start paying back the Obama administration for its $50 billion bailout and a U.S. Treasury spokesman said on Thursday that federal officials were notified of the management change, but not involved in it. The U.S. government owns a third of GM's outstanding shares.

Akerson also said the change had nothing to do with the company's performance in the first quarter, saying the fast start the company targeted was "intact."

AIMING FOR CEO JOB

Liddell left giant software company Microsoft, where he was CFO, in November 2009 to look for an even bigger job. When he joined GM, he was seen as a well-regarded outsider who could possibly succeed Whitacre when he stepped aside.

Liddell previously made it clear this was his ambition, and he repeated on Thursday that he had no interest in being a CFO at another company.

GM's board considered both Liddell and former Morgan Stanley banker Steve Girsky, now the company's vice chairman, as CEO candidates to succeed Whitacre after his sudden resignation last August on the brink of the IPO, people with knowledge of the process said.

But the board concluded that neither was the right fit at that time, prompting Akerson, 62, to step aside as a director and take the job himself.

Akerson said Liddell was a leader in GM's IPO, as well as running the finances through four consecutive profitable quarters. Liddell and Ammann were "the dynamic duo" in leading the company's finances, the CEO said, adding that he expects a seamless transition.

Analysts praised Liddell's performance during GM's investor road show last fall, when he wooed fund managers for the IPO by promising that the automaker would never again become "a $100 billion pension plan with a small company attached."

Barclays' Johnson said investors would want to clarify whether Liddell's departure signaled a change in "the conservative financial strategy" he had pushed.

Liddell had been paid a base salary of $750,000 at GM with no severance package. He also had been eligible for a stock grant of $3.45 million that would have been paid out over three years beginning in 2012.

Ammann, 38, joined GM in March 2010 and said on Thursday he would stay at GM over the long term. He and Liddell are both from New Zealand and have known each other about 20 years.

His successor in the treasurer's office will be announced at a later date.

GM shares closed down 2.6 percent at $31.42. Earlier, the stock hit a post-IPO low of $30.95, 6 percent below its IPO opening value of $33.00 and 22 percent below its high of $39.47 reached in January.

(Additional reporting by Bernie Woodall and Deepa Seetharaman; editing by Gerald E. McCormick and Andre Grenon)