WASHINGTON — The Pentagon is weighing a drastic plan to pull planes, ships, weapons and tens of thousands of U.S. troops from Europe, despite warnings from NATO allies about the growing threat of Russian aggression, according to seven current and former U.S. and Western officials.

The reduction could be roughly one-third of all U.S. troops in Europe, or about 25,000. A U.S. official and another person with knowledge of the deliberations say it could be even larger — as much as half, or up to 40,000 troops.