The United States faces a "cascading problem" of collecting about $64.8 billion owed to it by foreign nations, according to an unusually pessimistic report accompanying the $15.7 billion 1991 foreign aid bill that is scheduled to go to the House floor this week.

Drafted by the House Appropriations subcommittee on foreign operations, the report describes a worsening global debt picture in which loan reschedulings by rich countries increasingly are being used to paper over the extent of the crisis and postpone a day of reckoning.

"We have a mini S&L debacle on our hands with respect to international debt . . . a mountain of uncollectible debt," Rep. David R. Obey (D-Wis.) told the House Appropriations Committee last week.

"Debts owed to the U.S. government . . . represent an area where shenanigans in financial reporting often mislead people into believing that these debts can and will be repaid in full," the subcommittee report declared. It added that even a brief, moderate downturn in the world economy "would expose the true extent of the international debt crisis."

The bill that goes to the House this week includes three provisions aimed at easing the situation. One would revise the Arms Export Control Act to permit foreign countries to use military assistance funds to repay old U.S. loans for arms purchases. A second places restrictions on a $70 million U.S. contribution to the newly established European Bank for Reconstruction and Development in an effort to force forgiveness of Poland's huge debt by such lenders as West Germany.

The bill also gives the president authority to adjust Poland's debt to the United States "in a manner which recognizes {its} basic uncollectibility."

In an interview, Obey also called attention to the $22 billion in U.S. government loan guarantees outstanding from such major U.S. agencies as the Export-Import Bank, the Agriculture Department's Commodity Credit Corp. and the Pentagon's Defense Security Assistance Agency. DSAA is owed billions of dollars from foreign loans made in the 1970s and early 1980s to finance purchase of U.S. arms.

"We have a very serious problem there," said Obey. "As long as the economy functions worldwide, you can clank along like this. But what happens when we stop being lucky?"

At the end of May, the Export-Import Bank, which subsidizes U.S. exports with direct loans and guarantees, was carrying "delinquent payments" totaling $1.5 billion from about 50 countries, according to the bank's treasurer and comptroller, James K. Hess.

Under pressure from Congress, the bank has set up a $4.8 billion loan loss reserve -- public recognition that "it was unlikely that many of its loans were in fact fully collectible," according to the subcommittee report. Obey and other key Democrats have been demanding that the bank take a further step by seeking a major appropriation from Congress to beef up its capital reserves. But bank officials say that is unnecessary because the institution legally can refinance itself through Treasury Department borrowings.

"There's no S&L crisis here or anything like that," said Hess.

Under the foreign military sales program, U.S. defense contractors were paid by the U.S. government for arms shipped abroad. Now the government is having trouble collecting from some of the foreign customers.

Egypt's total debt to the United States is about $12 billion, of which about half results from old loans for arms purchases. As of last September, Egypt had fallen $630 million behind on its military payments and is facing $720 million in principal and interest due the U.S. government in the current year, sources said.

In a number of countries, debt incurred from old U.S. foreign aid programs comes close to equaling new aid. In 1990, according to the subcommittee report, "foreign military loan repayments alone represent 88 percent of the new econmic aid granted to Egypt."

According to the subcommittee report, the Paris Club, formed by lender nations to address the problem of government debt, has played a major role in postponing a reckoning by rescheduling loans -- stringing out the repayment period to lower the immediate costs of servicing loans. There were only six such reschedulings between 1968 and 1974. In 1987 and 1988, there were 29. Zaire's debt has been rescheduled nine times, Obey told the Appropriations Committee.

Meanwhile, the Polish government's commercial debt is worth 17 cents on the dollar, but commercial bankers continue to carry it on their books at full value -- an "accounting fiction," the subcommittee report said.