Federal regulators faced with widespread failures in the nation's savings and loan industry have used secret financing arrangements that vastly understate the costs, The Washington Post reported this week.

The Federal Savings and Loan Insurance Corp. has refused to give oversight committees in Congress documents that would reveal the hidden expenses, the newspaper reported, quoting unidentified government sources.The General Accounting Office, the congressional watchdog agency, has said FSLIC accounting techniques during this summer alone hid about $8 billion in costs that eventually must be paid by taxpayers, the Post noted.

The Federal Home Loan Bank Board and the FSLIC have promised billions of dollars to investors who have taken over failed thrifts in deals that do not appear in the federal budget and have not been approved by Congress.

Future claims on government funds that have been neither authorized nor appropriated by Congress present "a constitutional cataclysm" of uncontrolled spending, Rep. James Leach, R-Iowa, a member of the House Banking Committee, said last week.

FSLIC officials would not comment on any hidden agreements, the Post said.

The FSLIC was established to insure savings and loan deposits as high as $100,000. The corporation is supposed to pay depositors when an institution fails unless a cheaper solution is available, such as a merger or a sale.

Estimates of the cost of getting the thrift industry back on track range as high as $100 billion. Regulators have said contributions to the FSLIC from financially healthy institutions, along with profits from the sale of assets, will total $42.5 billion during the next 10 years - which they maintain is enough to meet costs without a full taxpayer bailout.

Critics insist more tax money may be needed. The Post also reported that Senate Banking Committee Chairman William Proxmire, D-Wis., would call in a speech Thursday for a $20 billion tax bailout of the industry.

The biggest off-the-book obligations for the FSLIC come in the agreements it has with investors who have taken over failed institutions, the Post noted.

To finance the transactions, the FSLIC issues promissory notes to investors and guarantees the principal and interest on loans by the struggling thrift institutions. Some of those loans have been written off as worthless. The interest the FSLIC is paying on the notes and bad loans ranges between 2 and 6 percentage points higher than the rate the agency would be required to pay if it borrowed from the Treasury, the Post said.

In a series of rescues during the last few weeks, the FSLIC promised aid that it said would cost $10.8 billion. But the GAO has listed the actual cost at more than $18 billion. the FSLIC figured its cost as if all the loans were to be repaid immediately, but the payments will be spread over the next 10 years and the interest expenses will make the actual cost much higher, the GAO said.

The Post said several bailouts also include hidden tax shelter benefits potentially worth millions of dollars to investors. Officials do not know how much the deals will cost the government in lost taxes, the newspaper said.