Argentina asked lenders to give it a 30-day extension on a $300 million loan repayment due yesterday as the country moved toward reforming its bankruptcy laws, which have been a major stumbling block in its relationships with foreign creditors.

If the banks fail to grant a waiver to Argentina, the big debtor nation theoretically could be declared in default on the debt, although bankers say it is doubtful any of the 265 banks involved in the loan would move to throw Latin America's third-largest debtor into default.

Many major Latin American borrowers have fallen in arrears on debt repayments before--including Brazil and Argentina--without being declared in default. But bankers said that they thought a 30-day waiver would be granted on the loan payment. A 15-day extension already has been granted. Argentina owes foreign lenders about $39 billion. Brazil owes $90 billion and Mexico owes more than $80 billion.

Reuter reported last night that Brazil has signed a new agreement with the International Monetary Fund after nearly four months of haggling over its domestic economy.

Once approved by the IMF board next month, the agreement should enable Brazil to settle the arrears on its foreign debt and start negotiations for more loans from commercial banks and governments, the Reuter quoted bankers as saying.

The new letter replaces one approved by the IMF last February during Brazil's first attempt to finance its debt. The fund suspended a $4.9 billion loan program in May when it became clear that Brazil was not meeting targets set out in the earlier letter. Commercial banks also halted their own lending.

There are many complicated issues involved in renegotiating the debts of the Latin American nations--which collectively owe about $320 billion to foreigners--and negotiators for the banks and the countries are tough and often do not reach an agreement until moments before a deadline.

As a result, the banker said, there always is a risk of a miscalculation by the banks, the debtor nations or even the IMF that could trigger a default.

The $300 million payment is the first installment on a $1.1 billion temporary loan banks made to Argentina last December to tide the country over until it could negotiate both a longer-term loan package with its lenders and a loan agreement with the IMF.

Although the banks agreed to a $1.5 billion medium-term loan late last month, they agreed not to disburse any of the money until the first refinancing of a maturing loan was completed. Like most debtor nations, Argentina needs new loans as well as easier terms on loans that are falling due.

But the banks put off signing the first refinancing agreement--a $220 million debt owed by the the government airline, Aerolineas Argentinas--because many of them were irate over a 10-year-old Argentine law that gives preference to Argentine creditors over foreign creditors during bankruptcy proceedings.

The preferential treatment of Argentine creditors has become a major point of issue in bankruptcy proceedings involving Celulosa, a major pulp and paper manufacturer that last February sought court protection for $300 million it owed 800 banks and suppliers. About 50 foreign banks hold $110 million of Celulosa debt.