PARIS — A day after the United States announced that it would be imposing tariffs on steel and aluminum imports from the European Union, Canada and Mexico, European leaders took the position that the move was an illegal and unnecessary act of protectionist hostility.

They warned that it would be met with retaliatory countermeasures. But E.U. officials emphasized that they are not in a trade war with the United States.

French President Emmanuel Macron, who otherwise enjoys a strong personal rapport with President Trump and who had lobbied against the tariffs during an April state visit to the White House, was unusually unsparing in his criticism.

Macron spoke with Trump on Thursday night and called the tariffs “illegal” and a “mistake,” according to a readout released Friday by the Elysee Palace.

The German government likewise declared in a statement: “We consider this unilateral measure to be illegal; the cited grounds of national security do not stand up.”

And British Prime Minister Theresa May said Friday that she was “deeply disappointed at the unjustified decision.”

Cecilia Malmström, the E.U.’s trade commissioner, said the 28-country bloc would file a complaint with the World Trade Organization and, by June 20, submit specific countermeasures. A previously published list of U.S. products that could face E.U. tariffs includes items with symbolic meaning, such as Kentucky bourbon, motorcycles and blue jeans.

“We are not in a trade war,” Malmström said Friday. “But we are in a very difficult situation caused by the United States.”

The dispute had some European foreign policy and trade specialists thinking back to the George W. Bush administration. In 2002, the Bush White House proposed similar tariffs but later withdrew them once the WTO deemed them illegal.

The key difference between then and now, European trade experts say, is tone.

“When Bush was putting tariffs up, there was always a side communication saying, ‘We have to do this for domestic reasons, and it’s not going to last forever. We’ll take it away soon,’ ” said Guntram B. Wolff, the director of Bruegel, a Brussels think tank that specializes in economics.

“Now, that side communication isn’t happening,” he said.

U.S. Commerce Secretary Wilbur Ross met with his European counterparts in Paris this week but was unwilling to bend on any demands.

In much of Western Europe, there is also the lingering memory of the “freedom fries” era, when U.S.-European animosity over the Iraq War in 2003 escalated to the point that some conservative U.S. lawmakers wanted french fries renamed in the House of Representatives cafeteria.

The disagreement over Iraq was seen at the time as a historic rupture to the transatlantic consensus. But the Iraq War represented a policy disagreement, political analysts note. To many in Europe, what’s happening now — with the trade dispute coming on the heels of the U.S. withdrawal from the Iran nuclear agreement and Paris climate agreement, as well as Trump’s decision to move the U.S. embassy to Jerusalem — represents a more fundamental break.

“In 2003, America was making a mistake,” said Dominique Moïsi, a foreign policy expert at the Institut Montaigne, a Paris-based think tank. “In 2018, America has entered a process of accelerated decline, which is unfortunately part of the decline of the West at large, part of the decline of democracy at large.”

“It’s as if there was too much America then but too little America now — or an America that’s too aggressive,” he said.

A key question from the European point of view, Wolff said, is whether Americans continue to support a president who is transforming their country’s persona on the world stage.

“There’s a big worry and miscomprehension about how the United States could have elected Donald Trump and accepts the rhetoric that is ongoing in Washington,” he said.

“We have a huge problem with the American government, with the White House,” said Moïsi. “But American society — is it behind Trump or not?”

In 2003, he said, the prevailing perception was that the American people supported Bush’s decision to invade Iraq, given the experience of the 9/11 terrorist attacks. Now, he said, there may be an important difference: “Let’s not break completely with America, because this is not America.”