Shares of General Motors Corp. (GM) extended their decline on Wednesday, losing another 4 percent, after news that billionaire Kirk Kerkorian's investment company sold 12 million shares.

GM's stock, already down 50 percent this year, fell to its lowest in more than 20 years after Kerkorian's Tracinda Corp. reduced its stake in GM to 7.8 percent from 9.9 percent late Tuesday.

The world's largest automaker has lost nearly $4 billion this year amid high health-care and materials costs, shrinking U.S. market share and sinking sales of large SUVs -- its long-time profit generators.

"Tracinda accumulating a 10 percent GM stake, much via public tender, bred speculation that value-creating strategic changes ... was more probable," Goldman Sachs analyst Robert Barry wrote in a research note on Wednesday.

"Now we expect that sentiment to reverse, at a time when fundamental pressures are growing, option value from UAW deals on health care and a North American restructuring is gone, and key restructuring architect, CFO Devine, is leaving."

GM plans to replace Chief Financial Officer John Devine with Frederick "Fritz" Henderson, chairman of GM Europe, as it launches a broader restructuring effort that will include the slashing of 30,000 jobs and closing of 12 facilities in North America.

GM shares fell 80 cents to $19.05 in New York Stock Exchange composite trading after hitting a low of $18.99 earlier in the day -- the lowest in more than 20 years after adjusting for the spin-off of Delphi Corp. in 1999.

Kerkorian said in a filing with the Securities and Exchange Commission that he sold his stock for $252 million to take advantage of tax savings stemming from his investment losses.

But Goldman's Barry said other issues likely influenced Kerkorian's decision, such as difficulty in selling GM's finance unit. "But simply realizing tax-related benefits seems less likely to us," he said.

The automaker has said it plans to sell its finance arm -- General Motors Acceptance Corp. -- to restore an investment-grade rating to the unit.

Barry also cited less upside from negotiations with the United Auto Workers union on restructuring plans and health-care concessions, less upside from new products and the failure to get a representative on the GM board.

Talks for a seat on GM's board for Kerkorian's top aid, Jerome York, broke down earlier this month.

But GM shares regained some ground briefly after UBS analyst Rob Hinchcliffe raised his rating on the stock to "neutral 2" from "reduce 2." He did, however, add that he expects the automaker to continue losing market share and burning cash in 2006.

Hinchcliffe also said the company's GMT-900 series -- a new line of redesigned SUVs and trucks to be launched next year -- is "not the savior for the company."

Adding to the pressure is a possible strike at bankrupt Delphi Corp. , GM's main auto parts supplier. Delphi has said it will ask the court to negate its labor contracts if it cannot reach a deal with its union.