Clayton, Dubilier & Rice and the Carlyle Group are part of a buyout group that plans to acquire Hertz, the largest American car-rental company, from Ford Motor for about $15 billion, people familiar with the matter said.

Clayton Dubilier of New York and Washington-based Carlyle, along with Merrill Lynch’s private-equity unit, have offered $5 billion cash for Hertz, plus they would assume about $10 billion of debt, said the people, who declined to be identified. A deal may be announced as soon as today, the people said. It would be the largest leveraged buyout since Kohlberg Kravis Roberts & Company paid $31 billion for RJR Nabisco in 1989.

Ford, the no. 2 American automaker, is selling Park Ridge, N.J.-based Hertz to raise cash as it loses market share to rivals led by Toyota. Ford’s North American business has been unprofitable for three of the past four quarters. Chief Executive Officer William Clay Ford Jr. has promised to increase earnings.

“The cash raised would be used to help fund Ford’s restructuring,” an analyst at Sanford C. Bernstein who has a “market perform” rating on Ford shares, Brian Johnson, said.

A Clayton Dubilier spokesman, Tom Franco; a Carlyle spokesman, Chris Ullman, and a Merrill spokeswoman, Terez Hanhan, declined to comment.

A Ford spokeswoman, Becky Sanch, and a Hertz spokesman, Richard Broome, also declined to comment.

Hertz rents cars from 7,400 locations in more than 150 countries. The company’s net income more than doubled last year to $365.5 million. Revenue was $6.7 billion. Ford earned $3.49 billion on net sales of $171.7 billion in 2004.

Ford has owned all of Hertz since 2001, when it spent $707 million to buy back an 18.5% stake that it had sold to the public four years earlier. Dearborn, Mich.-based Ford had considered selling shares of Hertz in an initial public offering before deciding to accept takeover bids.

Hertz has been in the car-rental business since 1918 and in the equipment rental business for more than 40 years. It has partnerships with more than 60 airlines, railroads, and hotel chains throughout the world, as well as with credit-card company American Express and Internet travel company Expedia.

Clayton Dubilier, Carlyle, and New York-based Merrill have been bidding for Hertz against a group that includes the Blackstone Group and Texas Pacific Group. A Blackstone spokesman, John Ford, declined to comment and a Texas Pacific spokesman, Owen Blicksilver, didn’t return calls.

Buyout firms have been joining forces this year to make bigger acquisitions. SunGard Data Systems of Wayne, Penn., whose software handles most Nasdaq Stock Market trades, was acquired last month by seven firms, including New York-based KKR and Blackstone, for $11.4 billion.

More than a record $190 billion of LBOs have been announced this year, data complied by Bloomberg show. Carlyle raised $7.85 billion in March for the biggest American buyout fund and New York-based Blackstone has received commitments of $12.5 billion for a global fund.

Ford is being advised by Goldman Sachs, Citigroup, and JPMorgan Chase. A spokeswoman for Goldman Sachs, Andrea Rachman, and a JPMorgan spokesman, Adam Castellani, declined to comment. A Citigroup spokesman, Jon Diat, didn’t return a call seeking comment.