NOT FOR the first time, President Clinton has made a bold promise to help the world's poorest countries. Last Wednesday he declared that the United States should forgive all the $3.5 billion-worth of non-concessional loans that it is owed by the most hopelessly indebted nations, rather than just the 90 percent that he had promised previously. The question is whether Mr. Clinton can get Congress to sign off on his proposed generosity.

The rich creditor nations first agreed to the idea of far-reaching debt relief in 1996, recognizing that many poor countries, notably those in Africa, were so deeply mired that even the best economic policies would never lift them out of poverty. Three years on, the fruits of that agreement are stunted: Only four out of the 40 or so most indebted countries have had their debts reduced. At the G7 meeting in June, and again during the past week's World Bank-IMF meetings in Washington, the creditor countries have pressed to speed up the process. Mr. Clinton's latest pledge is part of that effort, which aims to get help to most of the target countries by the end of next year.

Debt relief is not expensive. America is expected to pay only a small fraction of the total cost of write-offs, with other governments and multilateral institutions picking up the rest. The administration has asked Congress for $1 billion over four years to cover the American contribution, and it has suggested budget savings to pay for this. Rep. Spencer Bachus, a Republican proponent of debt relief, likes to say that debt relief costs just $1.20 per American for three years.

It is hard to believe that Congress would balk at that, especially since the relief is designed to go directly to humanitarian spending in poor countries. As Mr. Clinton said on Wednesday, America's prosperity is mirrored by countries where 40 million die of hunger annually and 1.3 billion survive on less than a dollar a day. These people cannot pay back money that corrupt rulers borrowed and then squandered. Congress should vote the money through.