Federal Deposit Insurance Corp. Chairman William Isaac is pushing a plan to offer insurance for bank accounts over $100,000 by using a combination of private and government insurance.

Under Isaac's plan, the FDIC would continue to insure the first $100,000 of bank deposits and would insure a portion of all bigger accounts. Banks would be allowed, if they chose, to buy private deposit insurance for any amount not insured by the government.

The FDIC chairman discussed his plan, which he called "one of the most significant reforms in banking in the past 50 years" with insurance executives and reporters yesterday.

He stressed that FDIC has made no decision to go ahead with the concept, which would require congressional approval.

If a bank fails now, depositors with uninsured deposits over $100,000 become creditors; they may have to wait years for bankruptcy proceedings to to get some of their money back.

Above $100,000, Isaac suggested, deposits might be 75 percent insured by the federal government. A depositor who had $500,000 in a failed bank would receive $400,000 immediately (instead of $100,000 under the current system). Private insurance would cover any remaining loss.

Bank failures are much rarer than government supervised mergers in which a healthy institution takes over a troubled one. In this case depositors all get their money back. Isaac believes this implicit government insurance encourages depositors to take excessive risks by seeking banks that pay the highest interest regardless of their soundness.