Warning that an international financial crisis is imminent, a group of monetarist economists yesterday urged the Federal Reserve and central banks in other countries to agree quickly on what steps they will take if major banks begin to fail.

The group, known as the Shadow Open Market Committee, said banks should be allowed to fail if they become insolvent because of poor management or loans gone bad. However, central banks should protect depositors while moving swiftly to act as "lenders of last resort" to keep the failures from also bringing down other basically sound financial institutions, the committee said.

The committee was formed 10 years ago in an effort to persuade the Federal Reserve to seek to control inflation and foster economic growth by providing only slow, steady increases in the money supply.

Large international banks are under great pressure because of the possibility that both private and government borrowers in many developing nations -- and in Eastern Europe as well -- will be unable to pay interest or principal on loans the banks have made, the committee said. Mexico, Bolivia and Poland already are unable to make payments on their debts.

In terms of domestic economic policy -- its usual focus, the committee recommended that the Fed seek about a 4.5 percent rate of money supply growth during 1983 and that the Reagan administration and Congress try to cut about $70 billion more from projected federal spending by 1985.

The committee was divided on whether there will be a substantial economic recovery in 1983 even if its policy recommendations are followed.

There was agreement, however, that, with a continued slowing in money growth, inflation would continue to fall, with prices rising no more than at a 5 percent rate next year.

The committee says that the greatest danger to the international banking system lies in countries such as Luxembourg and the Cayman Islands, which have no central bank but have become major banking centers as institutions have sought to avoid taxes and banking regulations in other countries.

The central banks should agree that each would be responsible for support of institutions, wherever they may be located, whose liabilities -- that is, their deposits -- are denominated in the currency of the country in which the central bank is situated, the committee continued.

"The insolvency problem looms very seriously," committee Co-chairman Karl Brunner of the University of Rochester declared.

The committee praised the Federal Reserve for having slowed the growth of money over the last three years, and said this has been responsible for the decline in inflation. At the same time, the cost of reducing inflation, in terms of lost output and high unemployment, has been unnecessarily high because the Fed has allowed money growth to fluctuate sharply from quarter to quarter, the committee continued.

Economist Allan H. Meltzer of Carnegie-Mellon University, the other co-chairman, who is just finishing a study of the issue for the Treasury Department, said the volatility in money growth has added three or four percentage points to interest rates in the last two years or so.

Committee member Robert Rasche of the University of Michigan believes the figure is considerably smaller, perhaps only one or one and a half percentage points.

As for the federal budget deficit, the committee said it is more important to reduce future rates of growth in spending than to try immediately to make large reductions in the prospective deficits.

With little or no economic recovery next year, the fiscal 1983 deficit could reach $200 billion, according to Rudy Penner, a committee member who is an economist at the American Enterprise Institute and who is favored by a number of members of Congress to succeed Alice Rivlin as director of the Congressional Budget Office.