NATO leaders agreed Thursday to endorse a United States missile defense system based in Europe and to provide more troops for Afghanistan, but they refused to back President BushÂ’s proposal to bring Ukraine and Georgia closer to NATO membership.WashingtonÂ’s failure to win over Germany, France, Italy, Spain and other crucial European countries to its view on Ukraine and Georgia was considered by some countries of Central and Eastern Europe to have sent a message of alliance weakness to Moscow, a day before the Russian president, Vladimir V. Putin, makes his first visit to a NATO summit. But Mr. Bush could claim success in persuading NATO to endorse his missile-defense plan in the face of Russian objections, and on Thursday signed an agreement with the Czech Republic to build radar for the system.