The federal rescue of American Savings Bank, a California thrift acquired by a group led by billionaire Robert M. Bass in 1988, will cost taxpayers $5.2 billion -- three times the government's original estimate, according to a General Accounting Office report released late yesterday.

The new estimate raises a question about whether it would have been cheaper for the government to close down American altogether, pay off its depositors and sell its loans and real estate on the open market. Although the GAO report did not address that issue directly, former federal regulators who made the agreement with the Bass group are likely to be asked about that today in testimony before the House Banking Committee.

The federal rescue, which included a complex set of guarantees, subsidies and tax breaks, has already helped turn American into a profitable company, and prompted critics to say that Bass and his partners won a sweetheart deal from the government. Last year, American reported profits of $214 million -- a better than 50 percent return for the Bass group on an initial cash investment of $400 million.

Reacting to the report last night, Bernard Carl, a Bass group principal who negotiated the American purchase, said, "I'm not sure the GAO is totally wrong." But Carl said that in arriving at its $5.2 billion figure, the GAO had computed the full 10-year cost to the government, including the interest the government would have to pay to borrow money for the American rescue. The original $1.7 billion estimate had been calculated by the now-defunct Federal Savings and Loan Insurance Corp. (FSLIC) in what accountants call "present value dollars."

In addition, the GAO report said FSLIC's cost estimate was based on assumptions about real estate conditions and interest rates that are different from those now used by those managing the thrift rescue.

Carl said he believes the government is still better off having made the deal. "If they liquidated the bank in December '88, it would have cost in excess of $5 billion," he said. Nonetheless, he expects political fallout from today's hearing before House Banking Committee Chairman Henry B. Gonzalez (D-Tex.) and his committee.

"I think Mr. Gonzalez and his colleagues have every right to be outraged that a bank should have been allowed to get in such a condition that taxpayers would have had to fork out $5 billion to solve the problem," he said. "I just hope they can distinguish between the cause and the solution."

The GAO's figures on the American deal were part of a larger report on the overall cost of 96 deals, involving more than 200 thrifts, arranged by FSLIC in 1988. The GAO concluded that the overall cost of reviving those institutions will be about $67 billion.

FSLIC initially estimated the 96 agreements would cost $61.9 billion. The American deal accounts for $3.5 billion of the $5 billion difference between the varying estimates.

The report said the cost of the '88 deals could go significantly higher if interest rates rise and real estate markets take more of a downturn than anticipated.

In addition to the GAO review, two separate reports are being prepared by lawyers and accountants on '88 agreements. One, expected next week, will consider whether the government can save money by modifying the terms of the deals; the second report, expected next month, will look at the competitiveness of the bidding process. Both were commissioned by the Resolution Trust Corp., the new government agency charged with the government's thrift rescue effort.

Among those slated to testify on the '88 agreements today are M. Danny Wall, former chairman of the Federal Home Loan Bank Board; Stuart D. Root, former executive director of FSLIC; and Thomas J. Lykos, Root's deputy at FSLIC.