BRUSSELS - The United States secured a diplomatic victory in Europewhen European Union officials agreed to postpone their proposal for a digital levy that threatened to derail a global effort to crack down on tax havens. The delay removes another potential obstacle to the broader tax agreement,which gained momentum over theweekend after finance ministers from the Group of 20 countries formally backed a new framework. That deal,which officials hope to make final by October,would usher in a global minimum tax of at least 15 percent and allow countries to tax large, profitable companies based onwhere their goods and services are sold. If enacted, the changeswould entail the biggest overhaul of the international tax system in a century.