In a thickly forested park bordered by apartment blocks and a playground, a dozen workers were busy on a recent day with chain saws and axes, felling trees, cutting logs and chopping them into firewood to be stashed in concealed sheds around Lviv, the largest city in western Ukraine.

Ironworkers at a nearby forge are working overtime to produce wood-burning stoves to be stored in strategic locations. In municipal depots, room is being made to stockpile reserves of coal.

The activity in Lviv is being played out in towns and cities across Ukraine, part of a nationwide effort to amass emergency arsenals of backup fuel and critical provisions as Russia tightens its chokehold on energy supplies across Europe.

As President Vladimir V. Putin slashes natural gas flows to Ukraine’s European allies, the government in Kyiv has accused Russia of also stepping up the destruction of critical infrastructure that provides heat, water and electricity to millions of homes, businesses and factories.

“All cities are preparing for a hard winter,” said Andriy Sadovyi, the mayor of Lviv, where Russian rockets knocked out three electrical substations in April, temporarily cutting power to neighborhoods. “Russia has turned off the gas to our neighbors, and they are trying to pressure us, too,” he said. “Our goal is survival. We need to be ready.”

The urgency escalated after Russia again curtailed gas supplies to Europe last week, leading the European Union to announce that it will reduce imports of Russian gas so as not to be held hostage. Russia turned off the gas taps to Latvia on Saturday, after the government there announced additional military assistance for Ukraine, the latest in a string of European countries to do so.

Ukraine buys its natural gas from European neighbors, so the restriction of deliveries to Europe threatens its access to energy, too.

Ukrainians frequently say they hope to defeat Russia by the time the cold weather arrives in October. But the leadership is also girding for the possibility of a drawn-out conflict in which Russia turns up the pressure by methodically strangling Ukrainians’ ability to keep warm.

Hundreds of thousands of civilians living in the Donetsk region of eastern Ukraine were ordered to evacuate this past weekend after months of relentless Russian bombardment destroyed the infrastructure needed to deliver heat and electricity.

“We understand that the Russians may continue targeting critical energy infrastructure before and during the winter,” said Oleksiy Chernyshov, Ukraine’s minister for communities and territories development, in an interview.

“They’ve demolished central heating stations in big cities, and physical devastation is still happening nationwide,” he said. “We are working to repair damage, but it doesn’t mean we won’t have more.”

Far from Ukraine’s embattled southeastern front, the campaign is being waged in forests and in steel forges, at gas storage sites and electrical stations, and even in basement boiler rooms, as the government mobilizes regions to activate a blueprint for amassing fuel and shelter.

Hundreds of thousands of cubic meters of firewood is being cut in forests around the country, Yuriy Bolokhovets, the head of Ukraine’s forest agency, said in a statement.

Under the government’s plan, so-called mobile heating units would be set up in cities of up to 200,000 people where shelling has cut heat or electricity, to help residents cope with outages until damaged infrastructure can be fixed.

Ukraine relies on a mix of natural gas and electricity generated by nuclear, hydro and fossil-fuel power stations.

In an unlikely twist, the war has left Ukraine with an electricity surplus after millions of people fled the country and economic activity slowed, lowering demand. The war sped up longstanding efforts to disconnect Ukraine’s energy grid from Russia and Belarus and link it directly to the European Union’s. Last month, Ukraine began exporting small amounts of electricity to Romania, with hopes of eventually supplying European companies that have been hit by Russian natural gas cuts, a potential source of valuable income.

But Ukrainian officials say the ability to supply electricity at home, especially over the coming winter, when temperatures can fall far below freezing, is increasingly threatened as Russia intensifies a campaign of targeting the infrastructure that delivers energy.

Russian shelling has hit thermal power plants around the country and over 200 gas-fired boiler plants used for centralized heating. Around 5,000 kilometers of gas pipelines have been damaged, along with 3,800 gas distribution centers, according to an analysis by the Woodrow Wilson International Center’s Kennan Institute, a think tank focused on Russia.

Gas is especially critical for Ukraine because it is used to warm thousands of high-rise apartment complexes, schools, post offices and municipal buildings that rely on centralized heating systems.

Naftogaz, the state-owned oil and gas company, maintains the largest gas reserves in Europe and has 11 billion cubic meters in storage. Andrii Zakrevskyi, head of the Ukrainian oil and gas association, said Monday that was enough to meet Ukraine’s needs before the war — but the level is roughly half what the government would like it to be.

While Moscow’s gas cuts have set Europe racing to secure new energy sources, the pain circles back to Ukraine, which imports gas from Europe after halting direct imports from Russia after the 2014 annexation of Crimea. Russia’s squeeze has pushed European gas futures prices to record levels, making imports more expensive at a time when the government in Kyiv is facing a budget crisis.

All of which has gotten the country mobilized in a hurry.

Swiatoslaw and Zoriana Bielinski recently stocked the cellar of their modest Lviv home with wood. The couple has purchased scores of batteries and several battery-operated lamps in case the lights go out, and they were preparing to buy gas bottles for cooking.

“We have to start thinking about this,” said Alicja Bielinska, Mr. Bielinski’s sister, who had helped the couple stock up. “Ultimately, we can survive without light and gas, but we won’t be able to survive if the invaders take over.”

Officials responsible for city planning have stockpiled on a much grander scale, collecting thousands of tons of wood and a large stash of coal in the last week alone. Mr. Sadovyi, Lviv’s mayor, said more supplies were on the way and has ordered thermostats to be lowered to 15 degrees Celsius (59 degrees Fahrenheit) when winter sets in.

On a recent day, Mr. Sadovyi buzzed around the city hall courtyard, greeting locals who had gathered for now-regular demonstrations on how to prepare for heat and electricity cuts — or worse. Two emergency workers showed residents how to put on a chemical suit in case of an attack: gas mask firmly in place, the suit sealed tight over the head.

Forges have shifted some production to put a priority on making tens of thousands wood-burning stoves, some emblazoned with the Ukrainian coat of arms. Town halls in over 200 cities are building stockpiles, along with tents that can house up to 50 people apiece in the event that multifamily apartment buildings are left without gas needed to heat them.

The tents can be moved quickly to sites without electricity or heat, providing emergency shelter and stoves for boiling water and cooking, said Mr. Chernyshov, the development minister.

“We hope we won’t have to use them,” said Iryna Dzhuryk, an administrative director in Lviv. “But this is an absolutely unusual situation. We are shocked by what we’re facing and worried about making sure we have enough to keep people warm.”

Nearby, sheds recently built to stock firewood have been camouflaged by locals. Additional wood is expected to arrive in the coming weeks, hewn from groves of trees inside the city and from the vast forests of western Ukraine.

One hour’s drive north of Lviv, in a dense wood streaked with yellow sunlight, forestry service workers labored to generate enough firewood to supply a beleaguered nation. On a recent weekday, they cut into a grove of weathered oak trees and trucked them to a sawmill, where a lumberyard half the size of a football field was stacked a meter high with freshly hewn logs.

Firewood sales have doubled from a year ago, and prices have nearly tripled as the country stocks up, said Yuriy Hromyak, vice director of the Lviv Regional Department of Forestry.

Even the forest isn’t sheltered from Russian attacks, he added. Ukrainian forces recently shot down a rocket fired from Belarus on a nearby oil storage facility. The tanks — which were empty — weren’t damaged, but the blast blew out all the windows in a wood storage warehouse and in parts of the sawmill.

“The Russians will do anything to try to destroy us,” he said. “But no one has managed to unite us as much as Putin has.”