In the leaked American intelligence documents, Ukraine’s predicament looks dire.

Missiles for its Soviet-era air defenses are projected to run out by May. Its position in the key city of Bakhmut is “catastrophic.” Its military has taken losses of more than 120,000 dead and wounded — less than Russia’s estimated toll, but enormous for a country with less than one third of Russia’s population.

Yet in Kyiv, Ukraine’s capital, this past week, there was little palpable alarm about the scores of pages of classified documents that have surfaced in one of the most remarkable disclosures of American secrets in the last decade. In fact, some welcomed the leak, hoping that it would emphasize what President Volodymyr Zelensky has been saying for months — that Ukraine urgently needs more ammunition and weapons to expel the Russian forces.

“From many points of view, this leak is really useful, and good, even I can say good for Ukraine,” said Oleksiy Honcharenko, a member of Parliament in the opposition European Solidarity party.

He said that unless Ukraine’s Western backers rushed to provide more than what he called “incremental’’ support, then “everything can go to waste, because so much is at stake today.”

The Pentagon intelligence updates and briefing slides that have dribbled into public view this month — after being posted on a gaming chat server by a 21-year-old Air National Guardsman, the authorities say — have offered new details about the state of the war. But they have not fundamentally altered the overall picture of it, according to Western analysts and policymakers.

They say the new material largely adheres to what they already knew about the war — and won’t upend how they are handling it.

“This doesn’t change our stance,” said Nils Schmid, the foreign policy spokesman in Germany’s Parliament for the Social Democrats, the party of Chancellor Olaf Scholz in the country’s three-way coalition. “We understand that now is the time to provide armaments to Ukraine.”

But as Ukraine prepares for a long-anticipated counteroffensive that could usher in a new phase of the nearly 14-month war, the documents are focusing heightened attention on Ukraine’s challenges, the shortcomings in Western military aid and the uncertainty of what comes next.

Whether Ukraine’s Western allies are going to be able to deliver what Kyiv needs in this crucial moment is a major open question. European officials say they are working to speed more artillery shells to Ukraine, but are acknowledging that they may not be able to reach the goal of delivering one million rounds this year.

“We can’t produce much more, at least not quickly,” said Ulrich Speck, a German foreign policy analyst. “Going forward, what can Europe still give? Now it’s harder, a realization we don’t have the ability to get things fast enough.”

Some analysts noted that the intelligence does not determine how the war will actually unfold. Ukraine’s allies vastly underestimated its capabilities in the past, predicting that Russian forces would overrun Kyiv in the opening days of the war. On top of that, the documents gauge conditions more than six weeks ago. Battlefield realities change fast.

But the leaked documents clearly show how heavily the war effort relies on the United States. American intelligence agencies have gotten inside Russia’s military enough to give real-time warnings to Ukraine on the timing of Moscow’s airstrikes, and even its specific targets. Several leaked slides show satellite imagery of the aftermath of Ukrainian airstrikes on what are described as “US-produced” targets in Russian-held territory — new evidence that the United States is providing precise targeting data.

One of the West’s biggest concerns about the leaks has been that Russia would scramble to find and seal off the sources of American intelligence. But in the week since the classified documents were posted widely on Telegram and Twitter, that fear has yet to materialize, two senior U.S. officials said: There is no indication that the Kremlin has taken steps to block the United States from penetrating Russia’s security and intelligence services.

Nor is there any sign yet that Russian commanders have changed their operations on the ground in Ukraine in response to the disclosures, the two U.S. officials said.

Beyond that, Ukrainian officials, while voicing their displeasure with the leaks, have told American officials that the disclosures will not seriously impact their planned offensive because Russia already knew the broad parameters of Ukrainian vulnerabilities (like its shortages of weapons and ammunition). And the documents did not disclose precisely when, where and how the Ukrainians would carry out their counteroffensive, one senior U.S. official said.

“It’s hard for me to believe this will dramatically change Ukraine’s short-term plans for its counteroffensive,” said Samuel Charap, a Russia analyst at the RAND Corporation. “There’s been discussion in open sources about the likely direction being south. Whether it affects the timing, perhaps.”

While the documents show that American spy agencies have intercepted Russian military communications, sometimes down to the details of planned Russian attacks, they offer little indication that the United States has been able to eavesdrop on the conversations of Russia’s leadership.

In the documents seen by The New York Times — which include many but not all of the hundreds of pages posted online — information about President Vladimir V. Putin and his inner circle appears mainly as hearsay. An entry describing a sensational plot by senior Russian officials to sabotage the invasion is attributed to a Ukrainian lawmaker “who received information from an unidentified Russian source with access to Kremlin officials.”

The lack of direct information about Mr. Putin could reflect the American intelligence community’s challenges in collecting information on a leader who has enveloped himself in an extraordinary cocoon of secrecy. Still, the documents offer only a small window into the breadth of American intelligence collection, leaning on information gleaned from electronic intercepts rather than on the C.I.A.’s network of human sources, which the agency guards much more carefully.

In Russia, many supporters of the war have warned that the leaks could be part of a ruse. The new details on the headwinds facing Ukraine’s military effort — including projections that key stocks of air defense missiles would be fully depleted by early May — are so extensive that some pro-Kremlin commentators have dismissed them as possible Western disinformation meant to get Russia to let its guard down.

“We would be happy if this were true,” a talk-show host on Russian state television, Olga Skabeyeva, quipped in a segment about the leaks last Tuesday.

But the documents also detail the Russian military’s myriad challenges and its devastating losses, offering a behind-the-scenes view into why Western officials believe that the war is likely to drag into next year. Russia’s slow-moving offensive in eastern Ukraine’s Donbas region “is likely heading toward a stalemate,” a Feb. 22 briefing slide predicts, with high Russian combat losses and diminishing munitions stockpiles “resulting in a protracted war beyond 2023.”

For some, that offers a reminder that the war is far more likely to end in some kind of negotiated settlement than with a decisive military victory for either side.

“We know that Ukraine needs to tilt the military balance in its favor to pave the way for negotiations,” Mr. Schmid, the German lawmaker, said.

For the cadre of analysts around the world parsing social-media videos and commercial satellite imagery to glean information about the war, the intelligence leaks have provided new data points. But several said they saw nothing that caused them to revise their fundamental views of the war, which also point to a protracted conflict.

One independent Russian military analyst, Ruslan Leviev, said the documents matched his prior conclusions, including his view that Ukraine’s challenges in mobilizing soldiers and obtaining ammunition meant the upcoming counteroffensive would not be able to deliver a decisive victory. Rob Lee, a senior fellow with the Foreign Policy Research Institute, said he had not seen anything that “changed my mind tremendously.”

But he warned that the outcome of Ukraine’s counteroffensive — and the war — rested on factors that even American intelligence agencies were hard pressed to measure, such as the morale of troops on both sides and how well they would perform.

“There’s a lot about this war that we still don’t know, or that we can’t have certainty about,” Mr. Lee said. “It’s war, and you can never have perfect information.”

Reporting was contributed by Helene Cooper, Julian E. Barnes, Alina Lobzina, Steven Erlanger, Matina Stevis-Gridneff, Christopher F. Schuetze and Catherine Porter.