As the Obama administration contemplates a third rescue of GMAC, the onetime finance arm of General Motors, federal officials, automotive executives and analysts all say the company is -- just like the biggest Wall Street firms -- too big to fail. Despite two taxpayer-financed bailouts, GMAC is still struggling, even as its two biggest customers, General Motors and Chrysler, have put bankruptcy behind them. While the collapse of GMAC probably would not send shock waves through the financial system the way the failure of a giant bank would, it would nonetheless deal a devastating blow to the auto industry, its suppliers and employees. GMAC, which lends money to buyers of GM and Chrysler vehicles, is racing to shore up its finances before a crucial Nov. 9 deadline, when federal regulators will evaluate its financial health. In a prelude to what is likely to be another direct government rescue, GMAC borrowed $2.9 billion in the bond market on Wednesday with the backing of the FDIC. But that money probably will not be enough to plug all the holes at GMAC, whose disastrous foray into subprime mortgages pushed the company to the brink of bankruptcy. GMAC is seeking as much as $5.6 billion in taxpayer money, on top of the $12.5 billion it received in two previous installments along with the growth in its lending responsibilities. The government has already pumped more into GMAC than it did into Chrysler. If the third rescue goes through, the government could wind up with a majority stake in GMAC. It currently owns 35 percent. Why rescue GMAC again? The federal government has committed more than $60 billion to prop up GM and Chrysler, and letting GMAC fail, the thinking goes, would threaten a recovery in the broader car industry. GMAC lies at the heart of the administration's industrial policy. It provides the bulk of loans to GM and Chrysler dealers to buy new vehicles from the companies, and is also the source of loans to consumers buying new vehicles. Other lenders have been reluctant to provide auto loans because sales of new vehicles have plunged this year to their lowest point since the early 1980s. GMAC is so interconnected with the industry that its failure would be devastating, according to many industry observers. 