The 87-year-old investor is seeking another 5% of GM in a move that could force big changes at the troubled automaker.

NEW YORK (CNN/Money) - Investor Kirk Kerkorian has bid for another 5 percent of General Motors Corp., a move that could force big changes at the world's largest automaker, which has fallen on hard times.

Tracinda Group, the investment firm for the 87-year-old investor, said it's offering $31 a share -- about 13 percent above where the stock closed Tuesday -- for up to 28 million shares of GM. That comes to about $868 million for a 4.95 percent stake in the Detroit-based automaker.

GM (Research) shares jumped about 18 percent in New York on the news, actually surpassing Kerkorian's offer price.

Tracinda already owns 22 million GM shares, or just under 4 percent of the stock, bought at an average price of $26.33 -- not far above the 12-year low GM stock hit in April. If the new offer goes through, Kerkorian would own about 8.8 percent of GM.

Tracinda's statement said it was making the offer for investment purposes only.

"Tracinda became aware of rumors over the weekend concerning its possible purchase of shares of General Motors stock," said the firm's statement. "Since Tracinda's acquisition of General Motors stock is solely for investment purposes, it decided to go forward with this tender offer to remove any uncertainty in the marketplace as to its investment intent."

One Wall Street analyst said the move could end in shaking up the troubled company.

"I think the result will be you'll have a shareholder activist with a significant but not controlling interest who will lobby for a restructuring," auto analyst Brian Johnson of Bernstein & Co. said. "For the first time, we could have someone who could look out for shareholders."

GM stock has tumbled further this year, after sinking last year, after the automaker warned in March that it was losing money in its core North American auto operations.

Following that warning, credit rating agency Standard & Poor's revised its outlook for GM to "negative" from "stable." S&P also cautioned that it could downgrade the company's debt to "junk" status at any time, which would likely raise its borrowing costs.

Johnson, who does not own GM stock, has a neutral rating on the shares and a target price of $27, below Tuesday's close.

While Kerkorian's offering an above-market price, he could be a winner if he forces GM to lower bloated health care costs for union employees and retirees, and slash excess manufacturing capacity, Johnson said.

"This highlights there is underlying value if the cost base could be restructured," he added.

Dave Cole, chairman of the Center for Automotive Research, said the move by Kerkorian focuses more attention on how much GM is undervalued at today's stock prices.

"People listen when he starts nosing around," said Cole about Kerkorian. "And it's more than nosing around when you throw hundreds of millions on the table."

Cole said that while the company's North American operation is losing money, portions of the business could be valuable to sell off, such as its finance division, GMAC. The division earned $2.9 billion in 2004, or about 80 percent of the company's overall earnings.

"GMAC is worth itself more than the value of the company today," said Cole. "They have a power train operation that could be spun off as an independent company."

And Cole said that even if GM's executive leadership feels threatened by Kerkorian's moves, the leaders are probably pleased with the leverage it gives them with unions, suppliers and other parties as they try to win cost cuts.

"Someone like (GM Chairman and CEO) Rick Wagoner is interested in raising pressure on everybody associated with the company. It's certainly not a time for people to be relaxed and doing business as usual," said Cole.

Still, those changes will be difficult, at least in the short run. United Autoworkers union officers have said they're not interested in reopening a contract that runs through 2007. Agreement from the union is needed for GM to cut health care costs or significantly cut U.S. staffing levels.

According to the tracking service LionShares, if Tracinda is successful in purchasing additional shares, it would be the No. 3 shareholder at GM behind two institutional shareholders.

Spokespersons at GM's largest shareholder, State Street Corp., as well as No. 2 shareholder Capital Research and Management Co. both said it is their firms' policy not to comment on their holdings or specific companies.

Kerkorian was once the biggest individual shareholder of Chrysler, before the No. 3 U.S. automaker was sold to Germany's Daimler Benz to create DaimlerChrysler.

Once an advocate of that deal, Kerkorian eventually sued DaimlerChrysler, charging Daimler management deceived shareholders by characterizing the 1998 deal as a merger of equals and paying Chrysler shareholders little in the way of a premium.

Kerkorian's suit had initially sought $8 billion in damages, but it was dismissed last month after a judge ruled Tracinda was sophisticated enough not to be deceived by Daimler leadership. By then Kerkorian had already sold most of his Chrysler stock at a sharp loss from its premerger value. But Cole said he still did very well on his Chrysler investment.

In addition to Chrysler, Kerkorian's high-profile holdings have included movie studio Metro-Goldwyn-Mayer, which he sold to a Sony-led group in April, netting him about $2 billion in cash.

He is still the majority owner of MGM Mirage (Research), which bought Mandalay Resort Group earlier this year, making it the world's largest casino operator.

Neither Kerkorian nor officials at Tracinda were immediately available for comment.

GM spokesman Jerry Dubrowski said the company had no comment on the announcement.

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