WASHINGTON - Seeking to bolster its credentials on global warming, the United States signed an agreement Tuesday with 13 other nations that calls for investing up to $53 million in companies that will profitably control emissions of methane, a greenhouse gas. Emissions of methane, mainly from landfills, are ranked second behind carbon dioxide emissions among industrial gases scientists blame for warming the earth's climate. "Today we're planting a seed," Mike Leavitt, administrator of the Environmental Protection Agency (news - web sites), told representatives of the countries at a ceremony co-sponsored by the American Petroleum Institute and the National Mining Association....