In a legally binding decision, the 15 nations of the European Union agreed yesterday to ratify the Kyoto Protocol on climate change by June. In doing so, the countries committed to an 8 percent total reduction in greenhouse gas emissions from 1990 levels — although they have not yet agreed on emissions targets for each country. The E.U. hoped the action would encourage other nations to ratify the accord prior to a U.N.-sponsored summit on sustainable development, to be held in South Africa in August. To take effect, the treaty must be ratified by 55 countries, including industrialized nations responsible for at least 55 percent of total global emissions. The refusal of the U.S. to participate effectively means that virtually every other industrialized country will have to ratify the treaty.