''It's hard to sleep at night,'' complained a leading West German commercial banker half seriously. He has billions in loans outstanding in some 120 nations, including large ones to Poland. Those Polish loans, and some others, are shaky.
The world's top commercial bankers, gathered here last week for the International Monetary Conference, have become more anxious about their countries' lending in the last year or so. In fact, there was some agreement among the bankers with the concern of one speaker, H. Frans van den Hoven, chairman of Unilever NV, who cited these facts:
* Perhaps $50 billion of debt, including country and corporate international debt, is in the process of being rescheduled. That means debtors can't repay money due promptly, and so they are being given a longer time, and sometimes better terms, for repayment.
* New international loans are now running at more than $150 billion a year. Adjusting for deposits of one bank with another, at the end of 1980 the net external claims of banks reporting to the Bank for International Settlements (in other words, the foreign loans of the great bulk of banks in the industrial countries) totaled $802 billion. That compares with $255 billion in 1975. Some 520 banks from more than 80 countries had established some form of office outside the country of their headquarters by the end of 1980.
* Of the $524 billion external long-term debt of 150 developing countries at the end of last year, two-thirds of the total was owed by only 13 countries.
* Whereas in 1971 only 34 percent of the debt of these 13 countries was owed to private creditors, by 1980 that figure had risen to 70 percent.
* In 1974 only three countries were in arrears on their external debts, to the tune of around $500 million. By last year 25 countries were in arrears, for at least $6.5 billion.
Other factors making these figures more worrisome, Mr. Van den Hoven said, were generalized stagflation in the major industrialized countries; continued and extreme volatility of interest rates and exchange rates; growing protectionism; and the worldwide phenomenon of high real interest rates (rates after subtracting the inflation rate).
He also spoke of growing political instability as a cause of adverse economic developments and an obstacle to remedial action.
''It is difficult to avoid the conclusion that a growing number of debt reschedulings is in the cards for the period ahead,'' he reckoned. Developing countries will have more difficulty servicing their debts because of protectionism, high interest rates, and recessions in industrial customer nations.
Moreover, the Dutch executive continued, there has been a deterioration in corporate balance sheets. They are using more short-term money that has rapidly varying interest rates.
''It is this dangerous confluence of country and company debt problems which sets the alarm bells ringing for me. . . . I can see little but danger on the horizon.''
Mr. Van den Hoven even wondered if the current efforts of bankers to restrain their international lending might provoke an alternative danger--''that of creating a vicious circle in which reining back lending exacerbates recession, leading to increased country and corporate distress.''
The German banker, who wished to remain unnamed, was also bothered by the possibility of banks suddenly retreating from the international loan business and thereby worsening the financial problems of nations and companies.
But to Alfred Brittain III, chairman of Bankers Trust Company, such concerns are ''overstated.'' Bankers, he argued, are prudent in their international loans. Top management keeps an eye on such business. They consult economic specialists and political scientists on ''country risk.''
Moreover, very few nations have actually defaulted on their loans, though a larger number have needed rescheduling.
The German banker noted that companies frequently disappear after bankruptcy, but nations do not.
Mr. Brittain admitted that ''everything isn't peaches and cream'' in the international lending business. ''We have more countries on the watch list than five years ago.''
Nonetheless, he added, the United States has never paid back its national debt entirely, merely refinancing it. Nor should one expect other countries to repay all their debts quickly. That doesn't necessarily mean they are going broke.
Alexandre Lamfalussy, assistant general manager of the Bank for International Settlements--a special bank for many of the central banks of the industrial nations--was not alarmed by the dangers of international loans. But he did point to some of the same hazards as Mr. Van den Hoven, such as high interest rates, disinflation, and weakening corporate balance sheets.
''The world has developed itself into a place which is more risky,'' he concluded.
Henry C. Wallich, a governor of the Federal Reserve Bank, maintains that one of the problems for commercial bankers has been getting an adequate spread between the cost of their money and the interest they charge on loans to developing countries. It was sometimes as low as 1/2 of 1 percent, and commonly 5/8ths of 1 percent. ''This has improved quite a bit lately,'' he said. That should give the banks more money to set aside as reserves against losses from bad loans.
Mr. Wallich noted, ''Bankers are in a more cautious frame of mind. But there is no panic.''