Billionaire investor Kirk Kerkorian is getting into the car business. Again.

Kerkorian disclosed yesterday that he has acquired a 4.7 percent stake in Ford Motor Co. and launched a tender offer to acquire even more shares, raising questions about his intentions for the troubled company.

His investment company, Tracinda Corp., purchased 100 million Ford shares for $691 million and offered to buy 20 million additional shares for $8.50, a 13.3 percent premium over Ford's closing price Friday. The added purchase would boost Kerkorian's holdings in Ford to 5.6 percent.

News of the offer drove Ford stock up 71 cents, or 9.5 percent, to $8.21. Tracinda said in a statement that Ford was starting to get "highly meaningful traction" in its turnaround and that it would continue to show "significant improvements in its results going forward."

The announcement raised speculation about the intentions of Kerkorian, 90, who has a long history of auto-industry activity, having invested in General Motors and Chrysler.