Finance ministers from the Group of Eight industrialized nations have announced agreement on a landmark deal to cancel more than 40-billion dollars in debt owed by the world's poorest nations. Britain' s treasury chief Gordon Brown announced the accord on Saturday after two days of talks in London involving the ministers of the world's seven leading industrialized countries plus Russia. He said the deal provides for the immediate cancellation of the debt of 18 countries, most of them in Africa, and eventually up to 20 others. The plan covers debts to such agencies as the International Monetary Fund, the African Development Bank and the World Bank. G-8 leaders of Britain, Canada, France, Germany, Italy, Japan, Russia and the United States are expected to give final approval to the plan at their summit in Scotland next month.