If the United States’ war with Iran evolved out of longstanding tensions over its nuclear program, the focus has shifted sharply to Iranian control over the Strait of Hormuz. The result is a chokehold on one-fifth of the world’s oil supply and an acrimonious dispute that has returned the two sides to open conflict.

Despite frequent assurances from President Trump that Iran has no navy and that the strait is open for passage, shipping traffic has plummeted amid renewed Iranian strikes on commercial ships. Diplomacy has essentially halted, and over the weekend, U.S. and Iranian forces continued to trade attacks in the region. Military experts assess that trying to open such a narrow, vulnerable passageway with force in the middle of a war would be a deadly, Sisyphean task.

Casting about for answers, one analytical group has floated a possible compromise model for the Persian Gulf. It’s based on a somewhat obscure, now-defunct treaty that once governed the collective production of coal and steel in Europe after World War II.

The group’s proposal, outlined in a report published this month, goes like this: The countries surrounding the Gulf would treat it as a shared territory — a regional commons of sorts — and charge a nominal fee only to oil tankers for the water’s maintenance. That could fall within international law, satisfy Tehran’s demand for enhanced control and give all eight states bordering the Gulf a stake in maintaining peace, the group said.

“If we can’t imagine a world where these countries are administering a nominal fee to do some maritime safety and environmental work, then that is sort of a bellwether of whether there’s going to be some pathway to a more durable regional peace,” said Esfandyar Batmanghelidj, the founder and chief executive of the Bourse & Bazaar Foundation, a London-based think tank focused on development and diplomacy in the Middle East and the broader region.

“Until we get this more basic kind of cooperation right, we’re not going to be able to move forward on the bigger things,” he added in a phone interview.

The main idea behind the proposal is that the Gulf situation is analogous to Europe at the end of World War II. Amid the struggle to recover from two bloody, devastating conflicts, Robert Schuman, France’s foreign minister, rejected trying to isolate Germany the way it was after World War I.

Instead, France and Germany worked together to produce coal and steel, two key components for armaments, under an agreement known as the European Coal and Steel Community. That rendered war between the two historical rivals “not merely unthinkable, but materially impossible,” Mr. Schuman said in a declaration in 1950.

France and Germany were joined by Italy, Belgium, Luxembourg and the Netherlands, a coalition that ultimately led to the European Union.

Achieving such a union in the Gulf would mean overcoming multiple obstacles, not least the diverging political agendas and historical rivalries. Still, the current alternative, trying to pry open the strait using military force, would be daunting.

The Pentagon has planned for decades for how to reopen the Strait of Hormuz in the event of a conflict, said Mara Karlin, a professor of national security issues at Johns Hopkins University who directed strategic military planning under the Biden administration as an assistant secretary of defense.

Mine sweeping is incredibly slow, strenuous work, and the few U.S. Navy ships designed to do it would be exposed, she said, so an armistice was always assumed as a precondition.

“Reopening has almost wholly focused on a permissive environment because it’s just seen as too difficult to try to reopen and go through this painstaking process of clearing mines when one attack restarts the whole mission,” she said. Planting just one new mine, or even threatening to plant one, can deter shipping.

Another method would be for the United States or some form of international coalition to provide escorts. This process was used by the U.S. Navy to protect Kuwaiti-flagged oil tankers under attack from Iran toward the end of the Iran-Iraq war in the 1980s. That set off frequent skirmishes with Iranian forces, and one warship that struck a mine nearly sank.

The years since have seen the development of much more nimble threats from Iran that include drones and missiles fired from mobile launchers or the fast attack boats employed by the Islamic Revolutionary Guards Corps, sometimes called its “mosquito fleet.”

“Maybe we can neutralize their capacity to interdict shipping, but all it takes is one mosquito boat, a couple of mines or a few drones to get through, and you’ve effectively blocked trade again,” said Ryan Crocker, a former U.S. ambassador to various countries in the region, including Iraq and Kuwait.

Neutralizing Iranian attacks would require extensive ground forces to control the long Iranian coastline, which would greatly ratchet up the risk of American casualties. “I think the calculation has been to date that we can reopen the strait, but not on a timeline or at a cost that was considered acceptable,” said Suzanne Maloney, vice president and director of foreign policy at the Brookings Institution.

Iran has insisted that Article 5 of the Memorandum of Understanding that the United States and Iran signed on June 17 gave Tehran full authority over restoring normal shipping. It has accused the United States of trying to undermine its negotiating leverage by opening an alternative shipping channel that skirts the coastline of Oman on the western side of the Strait of Hormuz.

In their report, Mr. Batmanghelidj and his colleague Mehran Haghirian at the Bourse & Bazaar Foundation point out that sprawling Gulf ports like Jebel Ali in Dubai already charge service fees to ships that use their facilities, so it would not be a major leap to grant similar authority instead to a supranational body that divided the proceeds.

The most logical step, the authors said, would be to apply such fees on the largest oil tankers that transit the Gulf annually, including 600 massive supertankers that make multiple trips. The yearly value of oil shipments is around $600 billion, according to the International Energy Agency. The carriers would barely notice a small surcharge, and the tankers pose the biggest risk for environmental damage, the report said.

Six Arab Gulf states — Saudi Arabia, Qatar, the United Arab Emirates, Kuwait, Bahrain and Oman, all U.S. allies — already belong to an organization called the Gulf Cooperation Council. Although generally effective when hammering out collective guidelines on mundane matters like industrialization, the organization is notoriously fractious when it comes to joint political action.

Adding Iran and Iraq to that mix could make the council even more volatile, a concern raised by some European officials, Mr. Batmanghelidj said. They view the Middle East as permanently riven by conflict, but France and Germany had the same reputation after World War II, he noted.

The major question is whether the United States and Iran would buy in.

The official Islamic Republic News Agency published a lengthy essay on July 10 expressing interest in a collective settlement, and it also reprinted the Bourse & Bazaar proposal.

“The Strait of Hormuz is not merely a passageway for the transfer of goods and energy, but rather an opportunity for regional cooperation,” the essay on IRNA said. “If managed properly, its economic and financial benefits can be shared more fairly among the countries of the region.”

Iranian national security “depends on preserving the ‘Iranian arrangements’ governing the Strait of Hormuz,” Gen. Mohammad Bagher Ghalibaf, the speaker of Iran’s Parliament and its chief negotiator, said in a statement on Wednesday. At the same time, “we must also use the tools of diplomacy and negotiations to achieve and realize our national interests,” he said.

How Mr. Trump might respond to such a proposal is anybody’s guess. Top U.S. officials, including Secretary of State Marco Rubio, have insisted that Hormuz return to the state of unfettered international navigation that was in place before the war.

That seemed to be Mr. Trump’s position. Then he suggested charging a 20 percent fee on all cargo in exchange for the U.S. Navy’s protecting the strait, before dropping the proposal after 24 hours.

So one main hurdle now, analysts said, is the lack of well-defined American policy goals. “I think the biggest negative now is uncertainty where the U.S. stands,” said Mr. Crocker, the former ambassador. “The Gulf states definitely need that kind of long-term U.S. assurance before they’re prepared to take any steps unilaterally or collectively.”

Shirin Hakim contributed reporting.