President Trump said on Wednesday that the United States would grant Ukraine a license to manufacture Patriot air defense systems, a move that could significantly bolster Kyiv’s ability to protect itself against Russian missile attacks that have escalated in recent weeks.

“We’ll give them the right to make Patriots,” Mr. Trump said during a meeting with President Volodymyr Zelensky of Ukraine on the sidelines of the NATO summit in Ankara, Turkey. “We’ll show them how to do it.”

But establishing the means to produce the weapons could take several years — time that Ukraine may not have as it confronts relentless Russian air assaults.

Mr. Zelensky had warned for weeks that Ukraine was running out of Patriot interceptors, the most reliable weapon that Western allies have given the country capable of shooting down Russian ballistic missiles. The mobile, surface-to-air defense system consists of advanced radar, a control van, and missile launchers, which fire the interceptors that stop ballistic missiles midair before they hit their targets.

The consequences of the shortage were laid bare on Monday, when Ukraine’s Air Force said it had failed to intercept any of the 23 ballistic missiles launched by Russia overnight. This week alone, Russian attacks have killed more than 50 people.

Ukraine has long pressed its Western allies for more Patriot interceptors, but manufacturing them is time-consuming and global inventories are under severe strain because of multiple conflicts around the world. The U.S.-Israeli war in Iran, in particular, used up stockpiles while driving up demand among Persian Gulf countries that Iran targeted in retaliatory attacks.

Mr. Zelensky has urged Washington to grant Ukraine a license to produce the Patriot interceptors, permission that the United States has given only to Germany and Japan.

“We have long made the case that we are capable of producing such defensive weapons ourselves,” Mr. Zelensky said in an evening address on Monday. “If Ukraine were granted U.S. licenses to produce Patriots, our own production would be sufficient both to protect Ukraine and to help partners in need.”

Mr. Trump said on Wednesday that Ukraine had the technical capacity to produce the advanced Patriot systems, praising the country’s booming defense industry. “They would be able to do it,” he said. “Most countries would not be able. They don’t have the talent. You have very talented people.”

The crucial question, however, is how quickly Ukraine can secure the license and begin producing Patriot interceptors.

The plan appears to be in its infancy. Mr. Trump said that his administration had not yet informed any American companies involved in manufacturing the Patriot systems of the decision to license production to Ukraine. “We haven’t informed the company of that yet, but that’ll work out all right,” he said, without naming the company.

Even once the license has been secured, setting up production of such sophisticated weapons would likely be a lengthy and technically demanding process.

For a start, Patriot interceptors are made up of many complex components that are often manufactured by subcontractors.

“The main issue with licensed production is it only makes sense if you can properly localize the supply chain,” said Fabian Hoffmann, a senior research fellow at the Norwegian Institute for Defense Studies in Oslo, a research group. “Final assembly is not the bottleneck. If I have all the components I can put them together in Ukraine.”

Another question will be whether a deal would be for the older model PAC-2 interceptors, made by RTX, or the more advanced PAC-3 interceptors, produced by Lockheed Martin. The latter are the most effective for shooting down ballistic missiles, Ukraine’s biggest vulnerability.