WASHINGTON — U.S. 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 U.S. 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.

Russian troops have advanced in the Donbas region of eastern Ukraine. They have clawed back more than a third of the territory that Ukrainian forces seized in a surprise offensive in the Kursk region of western Russia this year. The number of Russian drone strikes across Ukraine has increased from 350 in July to 750 in August and 1,500 in September.

“The situation is tense,” said a Ukrainian major stationed on the Ukrainian side of the border near Kursk who goes by the call sign Grizzly. “We are constantly losing previously occupied positions, the enemy has an advantage in men and artillery, and we are trying to hold the line.”

Gone is the Russian force that repeatedly stumbled as it invaded Ukraine in 2022. The Russian military, according to a senior U.S. military official, has evolved and is “on the march.”

As a result, some U.S. intelligence agencies and military officials are pessimistic about Ukraine’s ability to stop Russian advances as Kyiv tries to find ways to build up forces exhausted by nearly three years of war.

Still, Russia has fallen short of its own goals. Most notably, it has not been able to take the city of Pokrovsk, a logistics hub for Ukrainian forces. And independent experts say Russia’s shortages of radar, armored vehicles and, most critically, troops will come to a head next year.

Earlier this year, Ukrainian troops were struggling with shortages of ammunition supplies amid U.S. delays in approving more assistance.

Even after Congress approved more aid in April, Ukrainian officials have complained that the arms flowed too slowly, making it hard to resupply the front lines.

“This is the rule of the war,” President Volodymyr Zelenskyy said last week. “Because you have to count on very specific things in very concrete time. Otherwise, you can’t manage this situation. You cannot manage defending lines. You can’t secure people. You can’t prepare for the winter.”

On Oct. 29, Jake Sullivan, President Joe Biden’s national security adviser, and Andriy Yermak, a top adviser to Zelenskyy, met for two hours in Washington. They discussed the Biden administration’s plans to speed artillery systems, armored vehicles and air defense ammunition to Ukraine before the end of the year.

But U.S. military officials say weapons supplies are no longer Ukraine’s main disadvantage.

Ukraine has sharply narrowed Russia’s artillery advantage, U.S. officials said, and Ukrainian soldiers have used explosive drones to lay waste to Russian armored vehicles.

Ukraine’s biggest shortcoming now is troops, U.S. officials said.

Ukrainian officials have struggled to put in place a military draft that brings in enough troops. The country has hesitated to lower the conscription age, worried about the long-term demographic impact. Ukraine has limited itself to what one official called a more “democratic and measured” response to the shortage of troops, but as a result, it is running low on soldiers.

The Pentagon assesses that Ukraine has enough soldiers to fight for six to 12 more months, one official said. After that, he said, it will face a steep shortage.

Ukraine diverted some of its newly created brigades to support the incursion in Kursk instead of using them as originally planned to defend eastern and southern Ukraine or to build up reserves for an expected counteroffensive in 2025, Pentagon officials say.

“They’re working hard to bring more people on board,” Austin told reporters traveling with him, when asked about the troop shortages. “They’ve got to train those people. They have to regenerate combat power.”

A possible opening for Ukraine, however, might be Russia’s low supply of armored vehicles.

To offset its losses of advanced tanks, Russia tapped its huge stocks of far older tanks. But Ukrainian drones have destroyed many of Russia’s armored vehicles, particularly older models.

As a result, U.S. military officials say, Russia has relied on small infantry units to advance in eastern Ukraine. But American officials believe that many of the battlefields have become “a meat grinder” for Russian soldiers.

Mark Rutte, NATO’s new secretary-general, said last week that more than 600,000 Russian soldiers have been killed or injured since the start of the war. Those losses are behind North Korea’s deployment of about 10,000 troops to Russia, forces that Moscow wants to use to help push Ukraine out of Kursk, U.S. officials say.

An American military official said the decision to bring in those forces was “ill- conceived and desperate.”

Other Western diplomats dispute that the development is a sign of desperation and say it is a move meant to scare the West. Whatever the motivation, U.S. officials acknowledge that Russia is finding more troops and continues to sign up 25,000 to 30,000 new contracted recruits per month.

Russia’s success is partly a result of a shifting recruiting message, as it tells would-be soldiers that the war in Ukraine is really a fight against NATO, U.S. officials said. Russian bonuses have also drastically increased.

By combining these strategies, Putin may not need to order a politically unpopular broad draft, U.S. military and intelligence officials say.

But Russia’s resources “are finite, and Putin cannot reckon with these costs indefinitely,” the Institute for the Study of War said in a report last month.