About 150 credit unions, including the one at the House of Representatives, stand to lose a total of $20 million as a result of their dealings with the failed Penn Square National Bank in Oklahoma City.

All told, the credit unions had $106.3 million in uninsured deposits at Penn Square. The government has told the credit unions and other uninsured depositors they should expect to lose 20 percent of their uninsured funds invested with Penn Square.

Edgar F. Callahan, chairman of the National Credit Union Administration, said that despite the estimated losses of $20 million, no credit union is in danger of failing as a result of their Penn Square losses, based on information now available. But he said a number of unnamed credit unions have been "seriously affected" by the Penn Square situation.

The $30-million credit union at the House of Representatives, called the Wright Patman Credit Union, said it had $1 million on deposit at Penn Square, $900,000 of which is not insured by the FDIC. The federal government insures the first $100,000 in despoits. Jerry Roley, assistant manager of the House credit union, said the institution will have to take $180,000 of its Penn Square deposits as a loss. Roley said the credit union has more than $700,000 in reserves to handle such losses.

In addition to the credit unions, more than a dozen savings and loan associations reportedly will lose some of the money they had on deposit at Penn Square, which the government closed Monday. The Federal Home Loan Bank Board, which regulates savings and loans, refuses to discuss any potential problems for the institutions involved.

Credit union sources said the deposits at Penn Square offered interest rates well in excess of what was available at most banks. The House credit union was put in touch with Penn Square by a professional money broker--a firm hired by the bank to find large depositors.

Meanwhile, American Security Bank, the District's second largest, said in response to inquiries that it had bought some loans from Penn Square, but said the total was "insignificant" and would have no impact on the bank's income. A spokesman declined to reveal the amount of oil and gas loans it bought from the failed bank.

Continental Illinois National Bank, the nation's biggest business lender, bought more than $1 billion in energy loans from Penn Square. So many of those loans are bad that the bank is expected to deduct about $140 million to $160 million from earnings to increase its reserves for potential loan losses for the three-month accounting period that ended June 30. Continental, which analysts expected would report a $60 million profit for the second quarter, now is expected to report a $60 million loss.

A number of other major banks, anxious to expand their energy lending, bought loans from Penn Square. The banks included Seattle First National, Chase Manhattan, Northern Trust of Chicago and Michigan National. Penn Square, a shopping center bank only five years ago, sold more than $2 billion worth of loans to banks across the country. Its own assets grew from less than $50 million five years ago to more than $450 million.

But many of those loans, including the loans it made and then sold to other banks anxious to cash in on the oil and gas boom in Oklahoma, were to small, undercapitalized oil and gas drilling operations that could not handle the loan payments after the price of oil began to decline last year.

William Isaac, chairman of the Federal Deposit Insurance Corp., said that about $50 million worth of the bank's loans were uncollectable, much more than the bank could absorb and still remain solvent.

Monday night the Comptroller of the Currency, which regulates nationally chartered banks, closed Penn Square and turned the assets and the deposits over to the FDIC. The FDIC transferred all insured deposits to a special bank it set up, the Deposit Insurance National Bank of Oklahoma City. Penn Square depositors with accounts in excess of $100,000 were issued special "receiver's certificates" for the amount of their uninsured deposits.

When the FDIC sells off Penn Square's assets, holders of the receivers certificates, along with other general creditors of the bank, will receive a pro-rata portion of the proceeds of the sale.