The essential policy ingredients are the following: * Monetary expansion to reduce interest rates, support business investment and ease the problems of third world debtors.

Other third world debtors have fewer options, several analysts said.

Brazil is the biggest third world debtor, with a foreign debt of more than $120 billion.

What Mexico and the other third world debtors need is a resounding commitment by the U.S. to sizable debt reduction.

The Reagan Administration even made virtue of the muddle, asserting, for example, that banks could negotiate better deals with third world debtors without government help.

The Europeans say they are reluctant to establish a regrettable precedent for third world debtors.

When Japan announced this week it would provide $30 billion in credits to third world debtors, it was called a Marshall Plan.

Mr. Alfonsin called on creditors to reduce interest rates and extend repayment periods for all third world debtors.

Without new money, third world debtors will not have the resources to maintain even minimum growth while still servicing their debts.

Federal regulators have ordered that the nation's banks set aside more money to cover possible losses in loans to Brazil, the biggest third world debtor, bankers said yesterday.