NEW YORK (CNNMoney.com) -- General Motors and Chrysler LLC asked the government Tuesday for $21.6 billion in additional loans, but the final cost of a bailout of the auto industry could be significantly higher.

The two struggling auto giants have already received a total of $17.4 billion in loans. If they get the new loans they want, the price tag of the bailout would climb to $39 billion.

What's more, $7.5 billion in loans have already been approved for the financing arms of GM and Chrysler. Congress also approved funding last year for $25 billion in loans to help automakers convert their plants to produce more fuel efficient cars.

But dealers and suppliers are also asking for federal aid. And consumers may eventually get further incentives from the government to buy new cars.

All told, it could take up to $130 billion to save Detroit. Here's a breakdown of the rest of the money that might be needed.

Loan guarantees requested by auto parts suppliers: $18.5 billion. The trade groups for parts suppliers are asking loan guarantees for the amount they're owed by domestic automakers. They are also seeking guarantees on other types of commercial loans and help so General Motors (GM, Fortune 500) and Chrysler pay their suppliers more quickly.

Loan guarantees being requested by auto dealers: $5 billion to $20 billion. This is still in the works. But the National Automobile Dealers Association is working on a request for federal loan guarantees to make sure they can get the cash they need to finance their inventories. NADA vice president and general counsel Andrew Koblenz said the range is likely to be in the $5 billion to $20 billion range.

Line of credit being requested by Ford: $9 billion. Ford Motor (F, Fortune 500) continues to insist that it shouldn't need federal help, primarily because it locked up financing years before the credit markets dried up.

But in December, the automaker asked Congress to approve a $9 billion line of credit for the company in case sales were worse than expected or a rival's bankruptcy caused widespread failures in its own supplier or dealership base. Since that request, car sales have plunged further and forecasts for 2009 have grown increasingly bleak.

Tax credit for "Cash for Clunkers" program: $16 billion. There are a couple of different proposals floating around Capitol Hill to have the federal government give buyers of new, fuel-efficient vehicles a tax credit of up to $10,000 if they turn in an old, fuel-inefficient vehicle to be scrapped.

One version of the proposal, which would have been available for 1.6 million buyers, was briefly included in the economic stimulus package before it was stripped out. But stand-alone versions of the bill are still alive in Congress, and they have support of both the auto industry and environmentalists.

Allowing car buyers to deduct interest on auto loans: $9 billion. This proposal from Sen. Barbara Mikulski, D-Md., easily passed the Senate during debate on the stimulus bill. But it was stripped out of the final version, leaving a far more modest tax credit that allows buyers to deduct only the sales and excise tax they pay on a new car purchase.

Auto dealers and automakers were strong supporters of making interest deductible as a way to spur demand.

How to pay for it

If the Obama administration decides to move ahead with additional loans for GM and Chrysler, some think it may wrap all the various proposals into one auto bailout bill.

Still, there are questions about where future funding will come from. Much of the money for Detroit so far has come from the Troubled Asset Relief Program, the $700 bailout of the nation's financial system approved last fall.

But much, if not all, of the additional money will probably have to be approved by Congress, rather than just Treasury. That could prove to be an easier sell in this Congress though.

The House passed a $34 billion bailout for GM, Chrysler and Ford last December but it failed to win approval from enough Republicans in the Senate.

But the Democratic majority of both houses has grown significantly since then. So it is likely that a similar bailout measure would find the 60 votes needed to advance in the Senate, assuming all Democrats support it as they did the recently passed stimulus bill.

The automakers' strongest argument for getting the help to get the industry back on its feet is that it could cost the government far more if they fail.

GM and Chrysler both included estimates in viability plans submitted to the Treasury Tuesday about how much they would need to fund their operations if they went through a bankruptcy reorganization. GM said it could cost up to $100 billion in loans over two years, while Chrysler estimated it would cost between $20 billion and $25 billion.

Both companies said that if they went bankrupt, they would be forced to halt operations and liquidate if they did not receive the loans. And if they were to go out of business, lost federal tax revenue would reach into the hundreds of billions of dollars, according to company estimates.

Experts agreed that a bankruptcy at either company would be far more expensive for taxpayers than the amount of money they are asking for.

"There would be nothing standard about a bankruptcy filing at GM," said Michigan bankruptcy attorney Douglas Bernstein. "You don't normally have the government as your lender. And I don't think anybody has been through a bankruptcy of this magnitude."