The call goes out for collective action to solve world debt crisis

The biggest rescue operation in world financial history is under way. Senators heard top US credit managers, led by Federal Reserve chairman Paul A. Volcker, tell of efforts to control the $550 billion global debt problem.

''The international financial system still remains subject to extraordinary pressures,'' said Mr. Volcker, who urged Congress to help increase the lending authority of the International Monetary Fund (IMF), of which the United States is a partner.

In effect, some experts say, the world's credit structure is threatened by certain nonindustrialized countries that can't meet their debts. A default would affect US banks that have lent money abroad: ''A number of debtor countries have failed to make the necessary adjustments to rapidly changing economic conditions ,'' Comptroller of the Currency C.T. Conover told the Senate Banking Committee here, ''and, as a result, are having temporary difficulties making payments on their external loans.''

A feature of the testimony was the calm and low-key presentation by officials; actually many are concerned that the problem will go through the roof if it isn't handled with delicacy.

''The debt bomb-threat'' is how Time magazine described the situation (Jan. 19).

''Can we prevent a world economic crisis?'' asked international authority C.Fred Bergsten recently, answering his own questions ambiguously. He wrote: ''The developing countries alone owe over half a trillion dollars to foreign creditors. The East Europeans and troubled developed countries, such as Canada and Belgium, add substantially to that total. Outstanding loans by the nine largest US banks to Mexico and Brazil alone virtually equal their total capital and reserves'' (Challenge magazine, January-February).

Testifying here last week, Mr. Conover explained: ''Many US banks have large exposures to these countries that have become high risks. Several US banks have aggregate exposures exceeding 50 percent of capital to public and private sector borrowers in Mexico, Brazil, and/or Argentina.''

The problem for the international bankers is how to get the overborrowed debtor countries back to where the credit water isn't over their heads. Messrs. Volcker, Conover, and William M. Isaac, chairman of the Federal Deposit Insurance Corporation, urged Congress to make more credit available to the endangered countries by increasing funds to the International Monetary Fund.

Some senators worry about the risk, however, or refuse to accept the connection between the US Treasury and the world's banking problem. Messrs. Volcker, Conover, and Isaac, in a joint appearance and joint declaration before the Senate Banking Committee, asked for an expanded IMF. Tighter discipline on loans will be demanded henceforth, they said. In effect they said the horse hasn't been stolen, but the barn should be tightened anyway.

The three witnesses here presented a five-point statement intended to regulate foreign loans of US banks in the future. It is an international as well as a US problem, Conover said: The affected parties must take ''collective action'' involving ''multilateral institutions, Western governments, commercial banks, and borrower nations.''