The staggeringly high rate of Russian casualties in Ukraine means that President Vladimir V. Putin may not be able to achieve one of his key war objectives: seizing the entire eastern region of the country this year, officials in the Biden administration and military experts say.

With 500 Russian troops killed or wounded every day, according to the latest estimate by American intelligence and military officials, Russia’s war effort has decelerated to a grinding slog, the officials said…

“I think it’s safe to suggest that the Russians have probably taken 70 or 80,000 casualties in less than six months,” Colin Kahl, the under secretary of defense for policy, told reporters at the Pentagon on Monday, referring to deaths and injuries.

“They have made some incremental gains in the east, although not very much in the last couple of weeks, but that has come at extraordinary cost to the Russian military because of how well the Ukrainian military has performed and all the assistance the Ukrainian military has gotten.”