BRAZIL'S finance minister, after a week of talks here and in New York on his country's foreign debts, has ended them on an inconclusive and unreassuring note. It was an opportunity lost. Over the past year, governments and banks have carried out an impressive series of agreements to refinance Third World debt, beginning with Mexico's last fall through Argentina's currently. These agreements have increased the stability of the international financial system on which the prosperity of most of the world now depends. But the Brazilian case is the biggest of all these refinancings, and it is likely to be the most difficult.

Last February Brazil stopped paying interest on the money, some $78 billion, that it owes to foreign banks. In his visit here the Brazilian finance minister, Luis Carlos Bresser Pereira, left an impression that he feels no great urgency to resume payment. He seems to have concluded that, while the banks complain and the U.S. government grumbles, they are not prepared to do much about it. Brazil continues to get the short-term loans it needs to finance its trade, sometimes from the same banks to which it owes billions. Under those circumstances, it would be surprising if Mr. Bresser Pereira took anything but a very detached view of the debt negotiations ahead or the need for a prompt resolution.

For some years many people in this country and even more in Europe have proposed large write-offs to lighten the burden of the debts on the Latin economies. But the past debts are only half, or perhaps less than half, of the question that has to be answered. These economies must continue to borrow in the future if they are to develop their industrial power and raise their standards of living as they expect.

Mr. Bresser Pereira said Brazil wants to deal first with the banks and only later with the International Monetary Fund. The Brazilian position is that the IMF has a record of setting harsh conditions and interfering in Brazilian policy. But there's a little more to it than that. The Baker plan -- still very much alive, incidentally -- proposed a deal. The industrial world, led by the United States, would continue to provide financing for the developing economies if those governments, in return, undertook reforms to encourage growth.

The IMF is the key agency in monitoring those reforms. Some of them are deeply threatening to established business and political interests in Latin America. The United States and the IMF want to see protected markets opened to competition, for example. When Brazil says that it wants to negotiate with the banks first and the IMF later (if at all), it is saying that it wants new loans but is not prepared to proceed with the other half of the deal -- the economic reforms. The IMF replies that there will be enough new money to help Brazil continue to grow rapidly -- but not unless Brazil is prepared to commit itself to move toward greater efficiency. The real issue here is not a matter of financial technicalities. It's a political choice, and the choice is Brazil's.