BRNO, Czech Republic (AP) - The Czech prime minister told a summit of 15 European leaders Friday that a planned missile defense system, parts of which the United States wants to base in the Czech Republic and Poland, is vital to Europe's security. "The defense of Europe against missiles from some states and organizations is a necessary step which will significantly increase our security and also the security of our European allies and neighbors," Mirek Topolanek told the annual gathering of presidents from central, southern and eastern Europe.Earlier this week, U.S. officials traveled to Europe to discuss the proposal with their counterparts in Prague and Warsaw. The anti-missile system is also likely to be on the agenda when President Bush visits the two NATO members during a trip to Europe in June.