The action was the latest in a lengthy series of emergency government moves aimed at easing the worst credit crisis since the 1930s and limiting the severity of a year-long recession.
The Treasury Department said it would buy $5 billion in senior preferred equity with an 8 per cent dividend from GMAC as part of an effort to ensure the solvency of a company considered crucial to GM's survival.
It also said it would lend up to $1 billion to fund GM's purchase of equity in support of GMAC's reorganization as a bank holding company. That loan would come on top of assistance extended to the No. 1 US automaker earlier this month.
The government agreed on Dec. 19 to rescue GM and Chrysler LLC with up to $17.4 billion in loans to stave off a collapse that would have cost hundreds of thousands of jobs and dealt a severe blow to an economy already in recession. Of that amount, $13.4 billion was earmarked for GM.
President George W. Bush said at the time that it would be irresponsible to let the automakers die. The White House moved on its own after Republicans in the Democratic-controlled Congress blocked a deal to provide emergency funds.
US auto sales have plunged to 25-year lows in recent months and are not expected to recover substantially until after 2009 under the most optimistic of outlooks. The recent steep drop in sales, which automakers and analysts have linked to the credit crisis that took hold in September, has pushed both GM and its smaller rival Chrysler LLC to the brink of collapse.
The Treasury said it was dipping into a $700 billion financial bailout fund approved by Congress in early October to buy the equity in GMAC and extend the loan to GM.
GMAC won Federal Reserve approval to become a bank holding company last week, a move intended to give it freer access to emergency government funds and help it avoid bankruptcy. GMAC has had to raise additional capital to achieve bank holding company status.
The company, co-owned by GM and private equity firm Cerberus [CBS.UL], has lost $7.9 billion over the last five quarters as the credit crunch raised its borrowing costs sharply and the value of many of its assets plunged.
GMAC agreed to restrictions on dividend payments and executive pay as part of the equity injection. The bonus pool available to the top 25 executives was cut by 40 per cent from 2007 levels, a Treasury official told reporters on a conference call.
GMAC said in a statement that GM and a Cerberus management affiliate have agreed to buy $1.25 billion in new GMAC shares. Previously announced separate exchange and cash tender offers have been satisfied, it said.
Representatives of GM and Cerberus could not be reached for comment.
Ford Motor Co, the other firm in Detroit's storied Big Three, has said its liquidity was adequate for now and that it did not need a loan at this point.
GMAC has traditionally provided the bulk of financing for car buyers at GM dealerships and the floorplan financing that dealers rely on to carry inventory of GM cars and trucks.
But the finance company's ability to provide both kinds of financing has been sharply limited over the past several months because of the broader credit crisis and as GMAC's ability to borrow has shut down.
GM's US sales plunged 41 per cent in November and the automaker cited the crunch on GMAC's financing as contributing to the downward spiral in its sales. GM said earlier this month that while GMAC had been able to provide installment or lease financing to nearly half of GM car buyers just a year ago, that share had dropped to 6 per cent now.
In 2006, Cerberus paid $7.4 billion to GM for a 51-per cent stake of GMAC, which has also been hurt by its exposure to the troubled US mortgage market.