The United States and Ukraine agreed yesterday to work jointly to prevent the spread of biological weapons, signing a pact that clears the way for Ukraine’s government to receive U.S. aid to improve security at facilities where dangerous microbes are kept. The agreement, the result of more than a year of negotiations, was announced by Sens. Richard G. Lugar (R-Ind.) and Barack Obama (D-Ill.) during a visit to the Ukrainian capital, Kiev. The senators credited Ukraine’s reformist leaders, ushered into power by last fall’s Orange Revolution, with breaking bureaucratic resistance to the pact.Full Story