The new assessment of Mr. Putin’s intentions, which is shared by senior officials within the Biden administration, is to compel Kyiv to accept Russian claims to Ukraine’s southern and eastern territories. Having seized both Crimea and regions of Donbas in 2014, Russia seeks to secure a “land bridge” between western Russia and the Crimean Peninsula, and to expand Russian control of the Donbas region.

Mr. Putin would also continue his military pressure, including the pummeling of Ukrainian cities, calculating that it will lead Mr. Zelensky to abandon his hopes of joining the West and agree to a neutral status and other Russian demands.

Should Mr. Putin’s demands for territory and neutrality be rebuffed, he is expected to try to hold all of the ground his forces have taken, and fight on, U.S. officials said. “Based on our assessments militarily, it does appear that he is reverting to siege tactics,” said another U.S. official.