WASHINGTON — The Obama administration plans to announce on Thursday that it will scrap former President George W. Bush’s planned missile defense system in Eastern Europe and instead deploy a reconfigured system aimed more at intercepting shorter-range Iranian missiles, according to people familiar with the plans.

President Obama decided not to deploy a sophisticated radar system in the Czech Republic or 10 ground-based interceptors in Poland, as Mr. Bush had planned. Instead, the new system his administration is developing would deploy smaller SM-3 missiles, at first aboard ships and later probably either in southern Europe or Turkey, those familiar with the plans said. The White House will announce the decision Thursday morning and Defense Secretary Robert M. Gates, who was first appointed by Mr. Bush, will then discuss it with reporters at 10:30 a.m. It amounts to one of the biggest national security reversals by the new administration, one that will aggravate Czech and Polish allies and possibly please Russia, which has adamantly objected to the Bush system. But administration officials stressed that they are not abandoning missile defense, only redesigning it to meet the more immediate Iranian threat. Continua…