WASHINGTON — The government gave GMAC Financial Services another $3.8 billion in cash and took a majority stake in the auto lender, aiming to stabilize the company as it struggles with big losses in its home mortgage unit.

The fresh infusion is on top of $12.5 billion in taxpayer money Detroit-based GMAC has already received from the government. The new aid will boost the federal government's ownership in GMAC to 56 percent, from 35 percent, and means the U.S. now holds a majority stake in three companies it bailed out with taxpayer funds — GMAC, General Motors and insurer American International Group. The government also has taken control of mortgage giants Fannie Mae and Freddie Mac.

Keeping GMAC alive as it struggles with its mortgage loan problems has been a major component of the Obama administration's massive effort to rescue ailing automakers General Motors and Chrysler. The lender provides critical wholesale financing to thousands of GM and Chrysler auto dealers, allowing them to stock their showroom floors with vehicles.

That ability was crimped as loan losses mounted at GMAC's mortgage division — Residential Capital, dubbed ResCap. The company disclosed Wednesday it will take an additional $3.3 billion in mortgage-related write-downs, part of a $3.8 billion expected charge in the fourth quarter. GMAC also is preparing to sell off mortgage assets in an effort to reduce volatility.

GMAC's core auto lending business has shown some signs of revival even as auto sales slumped this year. The auto financing division earned a profit of $395 million during the third quarter.