Europe is on the cusp of a pivotal point in its yearslong quest to rid itself of Russian gas. In less than six months, the European Union will end the last of its Russian liquefied natural gas imports, a major step at trying to keep the Kremlin from using its abundant energy to fund its war machine.

To survive the shift, Europe has aggressively increased fuel imports, particularly from the United States. American producers now supply about two-thirds of European liquefied natural gas, a share that could rise to as much as 80 percent by the end of the decade. L.N.G. is gas supercooled to liquid form so it can be transported by sea in special tankers.

But the United States’ relationship with Europe is at a low point, eroded by President Trump’s frequent threats to impose tariffs, his periodic demands to control Greenland and the fissures over America’s decision to wage war with Iran.

That has engendered intense anxiety among defense and energy leaders who fear Europe is escaping the grip of a Russian gas monopoly only to hand Washington — and a mercurial American president — outsize leverage over its domestic energy policies.

“The reality is, the relationship has been massively fractured,” said Gen. Sir Richard Shirreff, a former senior commander of the North Atlantic alliance.

“To build dependency on America, with the greatest respect, at a time like this is not clever,” he said in an interview at a recent conference in London.

Seeking to break this cycle of reliance on the United States as well as other nations once and for all, European leaders put forward a plan on Friday to electrify the continent. The European Commission, the European Union’s executive arm, aims to shift rapidly to homegrown and renewable sources for industrial power grids, heating and transportation.

The proposal was designed to starve foreign energy suppliers of their leverage, while simultaneously slashing greenhouse gas emissions and lowering energy costs.

“The U.S. is certainly part of the solution for us in the short term, but in the long term we are on track to get rid of our dependency on natural gas altogether,” Dan Jorgensen, the European Union commissioner for housing and energy, said in an interview.

“From an economic perspective and a security perspective, we are in a very unsustainable situation and we need to get out of that,” Mr. Jorgensen said.

The European Union has already ended short-term contracts for liquid fuel imports from Russia. The ban on Russian liquefied gas under long-term contracts goes into effect on Jan. 1. One year later, Europe is set to eliminate Russian gas imports that arrive via pipeline.

For now, Europe is buying Russian gas at record levels. European imports of Russian liquefied natural gas increased 17 percent between March 18, when the European Union ban began phasing in, and May 31, compared with the same time period in 2025, according to the E.U. official data. Russian pipeline imports also increased, by 5 percent.

It is a volatile period in energy markets. Fuel like L.N.G. is bought far in advance, and the amount many hoped would be available now simply isn’t there.

As the fighting in Iran continues, Iranian strikes against Qatar, the world’s second largest exporter of L.N.G., also badly damaged the country’s export capacity. Qatar was not a major source of Europe’s liquefied gas before the war — between 6 and 8 percent. Still, the disruptions to gas flows from Qatar and elsewhere in the Middle East have scrambled global supplies and caused prices to spike.

A cease-fire in June between the United States and Iran briefly opened a window for tankers to transit the strait. But gas tankers have come to a virtual halt after that deal collapsed and both sides renewed attacks.

“Europe was counting on the fact that by 2027 there would be a lot of L.N.G.,” said Anne-Sophie Corbeau, a research scholar at the Center on Global Energy Policy at Columbia University. With the Iran war scrambling that calculus, “the situation is a lot more complicated,” she said.

Once Russian cargoes stop flowing, much of the gap will be filled by American liquefied natural gas. The United States currently supplies about two thirds of Europe’s L.N.G., compared with about a quarter of it in 2021. Nigeria and Qatar supply most of the rest. For natural gas delivered by pipeline, Europe heavily relies on supplies from Norway and Algeria.

American L.N.G. is attractive to Europe for a number of reasons, including the ease with which ships can travel back and forth.

But last month Chris Wright, the U.S. energy secretary, warned that a European climate regulation that aims to curb leaks of methane — a potent greenhouse gas — was overly burdensome and could cause American gas suppliers to sell to other regions instead.

“Without a meaningful reform of that rule, it is going to cause serious pain into Europe and that’s unnecessary,” Mr. Wright told Bloomberg in comments confirmed by his office.

“Our energy will flow,” Mr. Wright said. But he added, “It’ll just flow somewhere else.”

Ben Dietderich, a spokesman for Mr. Wright, said the remarks were not a threat. Rather, he said, they were explaining how the market would react if Europe proceeded with the regulation. But some Europeans said they viewed Mr. Wright’s comments as an ultimatum.

“They’re saying you need to buy more, and also please remove all your regulations,” Ms. Corbeau said. On Monday, the European Commission stopped short of ending the regulations, but proposed waiving penalties for three years on companies that fail to report or verify methane emissions.

Oil and gas industry officials in both the United States and Europe have pushed back on the notion that America may be an unreliable partner. The U.S. market is fundamentally governed by commercial contracts, not federal policy.

Fred H. Hutchison, president of L.N.G. Allies, which represents the U.S. export industry, noted that through mid-May alone, American companies this year have signed deals totaling more than 224 million tons per year.

“Companies do not voluntarily enter 15- to 20-year contracts with suppliers they believe to be unreliable,” Mr. Hutchinson wrote in an article for the Atlantic Council, a think tank based in Washington.

Nareg Terzian, head of strategy for the International Association of Oil and Gas Producers, a trade organization based in London, said he believed fears of European dependence on America were overblown.

“Those are raised as concerns by people who are not so happy to be using gas or L.N.G. in general,” he said. “Fundamentally, we believe that both the U.S. and the E.U. have an interest in keeping flows going, and we hope it’s going to stay that way.”