KUALA LUMPUR, MALAYSIA, JUNE 2 -- Fifteen developing countries have agreed on a joint stand on Third World debt, a move meant to strengthen their bargaining position with creditors and rich nations, a senior Malaysian official said today.

Ahmad Kamil Jaafar, secretary general of the Malaysian Foreign Ministry, told reporters the Group of 15 (G-15) would announce its stance Sunday. Collectively, the 15 owe about half of the total Third World debt of $1.3 trillion. They include some of the world's largest debtors.

"We are forging a position which can be used in our negotiations. If there is no common position you cannot deflect or minimize pressure" from rich nations, Ahmad Kamil said.

It was the first time that developing nations from four continents -- Africa, Asia, Europe and South America -- have united on debt. Leaders of Argentina, India, Indonesia, Malaysia, Senegal, Venezuela, Yugoslavia and Zimbabwe were joined by senior ministers from Algeria, Brazil, Egypt, Jamaica, Mexico, Nigeria and Peru at the three-day conference, which is to end Sunday. The group was formed during last September's Non-Aligned Movement summit in Belgrade.

Ahmad Kamil declined to give details of the agreement, which he said would be announced in a joint communique Sunday.

Malaysia has asked the Western creditors to be prepared to bear the risk of lending and to write off the debt of the least developed countries. Numerous officials called for a more comprehensive strategy of tackling world debt.

The industrialized nations rely on the Brady Plan, proposed by U.S. Treasury Secretary Nicholas Brady, to reduce debts that poor nations owe to commercial banks. Under the plan, the World Bank and International Monetary Fund advance funds to the nations, which in turn are bound to strict economic austerity policies. Under other provisions, the "Toronto Terms," the poorest debtors may obtain debt relief.

But some Third World countries have complained that some middle-income debtors, such as Nigeria, fail to qualify for either of these plans.

Ahmad Kamil said the joint G-15 position would be proposed to the Group of Seven, an economic forum of developing nations.

A senior delegate said envoys of five nations in the group also have called on French President Francois Mitterrand, a supporter of the G-15, to plead the case of Third World economic needs, including the debt issue, with rich nations.

France is a member of the Group of Seven along with the United States, Britain, West Germany, Japan, Italy and Canada, which will meet in Houston next month.