WASHINGTON — Taxpayers may be wondering why they're forking over more money to rescue yet another behemoth, Citigroup, even as their own nest eggs crack and jobs evaporate.

The answer is that the government has decided that guaranteeing hundreds of billions of dollars in possible losses and injecting $20 billion more into Citi trumps the alternative — a panic that could leave retirement accounts and investment portfolios of millions of Americans in tatters and shove more people out of jobs.

Whether the government's rescue of Citigroup Inc., announced late Sunday, will ultimately prove a good deal for taxpayers is hard to tell. In part, that's because no one seems sure what Citi's troubled assets are actually worth.

If the gamble pays off, Citigroup would be back on firm footing, unhinged financial markets would recover and taxpayers would turn a profit. If it doesn't, taxpayers would take a hit. And they would possibly have to rescue still more huge financial institutions, digging the bailout hole even deeper.

"It is way too early in this crisis to say whether it is a winner or a loser," said Cornelius Hurley, a professor and director of the graduate program in banking and financial law at Boston University. "I don't know if I am exhilarated by the prospect of being a shareholder in Citi or AIG. I'd rather have the money in my 401(k)."

Back in 1979, the U.S. guaranteed $1.2 billion in loans to Chrysler. When the struggling automaker rebounded four years later, the government reaped more than $300 million in profits.

The Bush administration, which leaves office Jan. 20, has decided that Citigroup, insurer American International Group and mortgage giants Fannie Mae and Freddie Mac are indeed too big to let fail.

Yet Treasury Secretary Henry Paulson has opposed using money from the $700 billion financial bailout to help teetering Detroit automakers or financially troubled homeowners. The bailout money, Paulson has said, was intended to stabilize the fragile financial system, including major banks.

Many in Detroit resent the fact that Citi and AIG received government bailout money while auto executives have been grilled, rebuffed and required to come up with plans to justify fresh federal loans.

Tim Leuliette, CEO of auto parts maker Dura Automotive Systems Inc. in Rochester Hills, Mich., said what the Detroit Three are asking for amounts to about 4 percent of the $700 billion Congress granted in the Wall Street bailout.

"I don't think the guys from Citi were there over the weekend getting grilled when they got their $20 billion last night," Leuliette complained.

The case for rescuing Citigroup, a company with more than 200 million customers and operations in more than 100 countries, may be more persuasive than the case for smaller banks whose reach doesn't extend so far. Still, the government action makes other financial companies more likely to seek federal aid.

President Bush held open the prospect yesterday of similar arrangements should other companies falter. And Paulson could still decide to tap the second $350 billion installment of the $700 billion package.

Treasury and the Federal Reserve are considering using some of the bailout funds to create a new loan facility to help firms that issue credit cards, and make student and car loans.

The Treasury chief has been hammered by critics in Congress and elsewhere for his handling of the $700 billion bailout, especially for frequent and confusing shifts in strategy. Paulson abandoned an initial approach to buy rotten mortgages and other bad assets from banks and focused instead on buying ownership stakes in banks.

"Paulson is doing a poor job of explaining this to Mr. and Mrs. Kettle, but it is tough to explain all of this in a sort of sound bite," said Sean Snaith, economics professor at the University of Central Florida.

The $20 billion from the Treasury Department will come from the $700 billion package. The capital infusion follows an earlier $25 billion infusion in which the government also received an ownership stake. That earlier $25 billion was part of a capital injection program for major banks.

As part of the plan, Treasury and the Federal Deposit Insurance Corp. will guarantee against the "possibility of unusually large losses" by Citi on up to $306 billion of risky loans and securities backed by commercial and residential mortgages.