n a sign that the United States and its allies believe that the fighting in Ukraine will last years, military officials from more than 40 countries gathered at NATO’s headquarters in Brussels on Wednesday to discuss how their governments can ramp up production of arms and ammunition.

The meeting was held under the auspices of the Ukraine Defense Contact Group, which the U.S. Defense Department created after Russia invaded the country in late February.

The top civilian and uniformed military leaders of member nations meet monthly to review Ukraine’s needs and requests, and their pledges of support. But on Wednesday, the government officials responsible for purchasing weapons — “national armaments directors,” as the Pentagon calls them — met as a group for the first time. William A. LaPlante, the Pentagon’s top acquisitions official, led the closed-door session.

After months of shipping billions of dollars’ worth of weapons to Ukraine, the donor countries now find that they need to make more munitions to continue the flow as winter approaches. But increasing production is not necessarily something that can happen overnight.

A senior NATO official said delegates discussed gaps in weapons stockpiles and how to coordinate manufacturing to fill them quickly, for fighting that he predicted would reach a critical point in the coming months.

The official, who spoke on the condition of anonymity because he was not authorized to speak publicly, did not offer specifics on which weapons might next be sent to Ukraine, and American officials would not comment on the discussions. So far the Biden administration has provided Ukraine with nearly $16 billion in security assistance, including 21 separate packages of military aid from Pentagon stockpiles.

Weapons procurement and delivery can take years to complete, but the NATO official described some short-term fixes, including agreement among multiple countries to buy more ammunition, largely to backfill stockpiles reduced by the war.

He said that would play into a longer-term effort to bolster and share munitions, make them compatible with weapons systems across borders and inject more urgency into a process that was adjusting to what he described as a different security environment.

More than 40 nations attended the group’s inaugural meeting at Ramstein Air Base in Germany on April 26, including all of the countries in NATO, several European nations that hope to join and eight so-called “major non-NATO allies” from Africa, the Middle East, Asia and the Pacific. Since then, a few countries from the Americas have also signed on.