American military and intelligence officials have concluded that the war in Ukraine is no longer a stalemate as Russia makes steady gains, and the sense of pessimism in Kyiv and Washington is deepening.

The dip in morale and questions about whether American support will continue pose their own threat to Ukraine’s war effort. Ukraine is losing territory in the east, and its forces inside Russia have been partially pushed back.

The Ukrainian military is struggling to recruit soldiers and equip new units. The number of its soldiers killed in action, about 57,000, is half of Russia’s losses but still significant for the much smaller country.

Russia’s shortages of soldiers and supplies have also grown worse, Western officials and other experts said. And its gains in the war have come at great cost.

If U.S. support for Ukraine remains strong until next summer, Kyiv could have an opportunity to take advantage of Russia’s weaknesses and expected shortfalls in soldiers and tanks, American officials say.

U.S. government analysts concluded this summer that Russia was unlikely to make significant gains in Ukraine in the coming months, as its poorly trained forces struggled to break through Ukrainian defenses. But that assessment proved wrong.