With continued American aid to Ukraine stalled and against the looming prospect of a second Trump presidency, NATO officials are looking to take more control of directing military support from Ukraine’s allies — a role that the United States has played for the past two years.

Under a proposal being discussed this week at the military alliance’s headquarters, NATO would oversee the Ukraine Defense Contact Group, a group currently led by the United States that coordinates the donation and delivery of weapons to the battlefield. Discussions are also underway about a plan floated by Jens Stoltenberg, the NATO secretary general, to secure an additional $100 billion from the alliance’s 32 member states for Ukraine over five years.

“A stronger NATO role in coordinating and providing support is the way to end this war in a way where Ukraine prevails,” Mr. Stoltenberg said on Wednesday at the start of meetings among the alliance’s top diplomats.

“There is a need to give this a more robust and institutional framework to ensure predictability and commitment for the long haul,” Mr. Stoltenberg said. He added: “I strongly believe it’s important that allies make decisions fast. And that includes, of course, the United States.”

Mr. Stoltenberg would not discuss specifics, but he said he hoped to have the new efforts approved in time for a July summit meeting of NATO leaders in Washington, where officials are expected to again debate when Ukraine might be allowed to join the military alliance, as has been promised for years.

A NATO official confirmed the proposals, which were reported earlier by news outlets including Bloomberg News.

It is not clear whether they will be approved at all, however. A second NATO official said that Hungary, where Prime Minister Viktor Orban has maintained warm relations with Russia, opposed the effort to put the Defense Contact Group under the alliance’s oversight. And several allies have questioned how NATO would be able to corral the $100 billion when it has no leverage to raise money among member states, the official said. Both NATO officials spoke on the condition of anonymity, because the details of the plans have not been publicly released.

It was also unclear whether Washington would support such changes. Lloyd J. Austin III, the American defense secretary, called the group’s current format “a very effective forum” when asked last month about the prospect of moving it into NATO. Secretary of State Antony J. Blinken was delayed in arriving to Wednesday’s meeting but was expected to attend.

The alliance has previously been reluctant to take on a greater role in the war in Ukraine, given fears of provoking a wider and more severe military response from President Vladimir V. Putin of Russia, who already views the conflict as a proxy war between his nation and NATO.

But Washington’s support for Ukraine has wavered in recent months. The United States has continued to wrangle over a $60 billion aid package for Ukraine that congressional Republicans have stalled for six months, although Speaker Mike Johnson is expected to try to push through legislation when lawmakers return to Washington next week.

The delay has infuriated Ukraine, irritated allies and prompted Mr. Stoltenberg to declare on Wednesday that it “has consequences” on the battlefield, where Ukraine’s forces are running out of artillery and air defense systems as Russia gains ground in key areas along the front line.

Concern is also growing among NATO allies over the possible re-election in November of former President Donald J. Trump, who in the past has vowed to withdraw the United States from the military alliance and recently threatened not to defend Europe if it were under attack. Mr. Stoltenberg sidestepped a question on Wednesday about Mr. Trump, but said that “you need long-term planning” for NATO to continue supporting Ukraine.

In the two years since Russia’s full-scale invasion of Ukraine, the United States has led an effort to funnel more than $88 billion in weapons and security assistance to Kyiv through the Ukraine Defense Contact Group, which usually meets at an American air base in Ramstein, Germany. The group includes about 50 countries and international organizations, including some that are not NATO members.

It is not clear how the NATO alliance would work with nonmember states. But Mr. Stoltenberg noted that NATO states provide 99 percent of the military aid that Ukraine receives. He also said what was “obvious is that we need new and more money for Ukraine, and we need it over many years.”

Beyond the new proposals, NATO has little to offer Ukraine for the rest of the year, especially given that the United States and Germany insist that Kyiv must make democratic and security reforms before it can become an alliance member.

Ukraine’s foreign minister, Dmytro Kuleba, is scheduled to meet top NATO diplomats at headquarters on Thursday, the official 75th anniversary of the military alliance that was created at the start of the Cold War in a collective security pact against the Soviet Union.

Its latest member is Sweden, which abandoned decades of nonalignment after Russia invaded Ukraine in 2022. Sweden joined the alliance formally this year, and Wednesday was the first time its foreign minister, Tobias Billström, joined the diplomatic discussions as a full NATO member.

Matina Stevis-Gridneff contributed reporting.