Chile's major commercial bank lenders agreed to loan the debt-laden nation $1.085 billion this year, $150 million of which will be guaranteed by the World Bank.

The banks also agreed to stretch out for 12 years the $6 billion of Chilean debt that comes due between 1985 and 1987. The rates on both the new loan and the rescheduled debts are lower than Chile had to pay last year.

Chile, which has $20 billion in foreign debts, is Latin America's fifth-biggest borrower. Despite adopting tough austerity programs, the country is having a difficult time rebuilding its economy and improving its international financial situation because of the low price of copper. Copper accounts for about half of Chile's exports.

The Chilean agreement, which still must be approved by all of Chile's 300 lenders, is the first commercial bank loan to a Latin American debtor nation that includes a guarantee by the the World Bank, the multilateral development agency.

Initially, the World Bank, Chile and commercial banks had contemplated a $250 million World Bank guarantee, but the United States resisted involving the bank in a straightforward guarantee of a commercial loan.

The package announced by Susan Segal, senior vice president of Manufacturers Hanover Trust Co. -- the chairman of the Chilean bank advisory committee -- includes $785 million of straight bank loans plus a $300 million loan for Chilean road development. The World Bank will guarantee half of the road loan -- which is typical of the type of development financing carried out by the institution -- and provide an additional $140 million of its own money for the project.

But banking and government sources said the road development loan was a method devised by the World Bank and commercial banks to inject more desperately needed dollars into Chile and avoid the U.S. objections. Chile had planned to finance the road renovations out of domestic funds.

Chile will pay an interest rate of 1 5/8 percentage points above the London Interbank Offered Rate (Libor) -- the rate banks in London charge each other to borrow short-term -- or 1 1/4 points above the U.S. prime rate. Last year, the country paid 1 3/4 points over Libor, or 1 1/2 points over prime. The loan must be repaid within nine years, and for the five years Chile must pay only interest.

For the rescheduled loans, Chile must pay 1 3/8 over Libor. It has 12 years to repay, with a six-year grace period on principal. The higher rates Chile had to pay on loans it rescheduled in 1983 and 1984 were reduced to 1 3/8 over Libor as part of yesterday's agreement.

Chile gave in to bank demands that the foreign debts contracted by its private banks should be guaranteed by the Chilean government. More so than in many Latin American countries, Chile used its private banks to borrow needed dollars. Bank loans are included in the $6 billion of maturing debts on which repayment was extended.