WASHINGTON -- The White House will shelve Bush administration plans to build a missile-defense system in Poland and the Czech Republic, according to people familiar with the matter, a move likely to cheer Moscow and roil the security debate in Europe.

The U.S. will base its decision on a determination that Iran's long-range missile program has not progressed as rapidly as previously estimated, reducing the threat to the continental U.S. and major European capitals, according to current and former U.S. officials.

The...