By Andrew Gray and Lili Bayer

BRUSSELS (Reuters) - Even as they have rallied to Volodymyr Zelenskiy's side after his Oval Office clash with Donald Trump, European leaders' approach to the war in Ukraine and the continent's security remains highly dependent on the U.S. president.

For all their sympathy for Zelenskiy and European anger at his treatment by Trump, they see no way to bring peace to Ukraine or protect Europe against Russia without U.S. support.

That view reflects a harsh reality for Europeans that U.S. hard power is vastly superior to anything they can muster, even as they scramble to ramp up defence spending and vow to take more responsibility for their own security.

Whether Europeans can still rely on that power to come to their aid, as they have done for decades, is an existential question not only for Ukraine but for the continent’s security and the NATO alliance.

Even after Trump's public berating of the Ukrainian president, European leaders are essentially sticking to the strategy they have pursued since the U.S. president began his second term.

It is the same for both Ukraine and broader European security: try to keep the U.S. engaged while also boosting Europe’s own efforts.

"Do we consider Volodymr Zelenskiy an important resistance fighter, a hero? The answer is yes. Should we be making judgment or taking the moral high ground? Then the answer is no," French Foreign Minister Jean-Noel Barrot told RTL Radio on Monday.

The European strategy was on display at a leaders' meeting in London on Sunday and will likely feature again at a European Union summit on Ukraine and defence on Thursday in Brussels.

Leaders including NATO boss Mark Rutte urged Zelenskiy to find a way to rebuild ties with Trump.

And even as he declared Europe is ready to do the "heavy lifting" on security guarantees for Ukraine after a peace deal, British Prime Minister Keir Starmer said they would need "strong U.S. backing" - which Trump has not promised so far.

STRATEGY DOUBTS

Some doubt whether such a strategy has much chance of success, given Trump’s treatment of Zelenskiy and his swift moves to warm up U.S. relations with Russia.

"It seems to me that many have still not fully accepted that Trump simply does not want to play the role that Europeans want him to play," said Jana Puglierin, head of the Berlin office of the European Council on Foreign Relations think tank.

"No 'strong US backing' will materialize," she posted on X in a comment on Starmer's remarks.

However, European officials feel they have no alternative but to keep trying, even though some were privately fuming over how Trump treated Zelenskiy.

One senior official declared in the aftermath of the blow-up: "Donald Trump has to choose if he wants to call himself a leader of the free world, or leader of an extortion gang. The latter is not interesting for Europe."

Another branded the episode "disgraceful" and an official from northern Europe called it an "utter disgrace".

But Peter Mandelson, the British ambassador to the United States, said Ukrainian-U.S. relations needed to be reset as Trump’s initiative to end the war was "the only show in town".

PRESSING CONCERN

For Ukraine’s European allies, one pressing concern is that U.S. arms deliveries approved under the Biden administration keep flowing.

According to NATO, the U.S. provided more than 20 billion euros ($21 billion) in security assistance to Ukraine in 2024 – more than 40% of the total received by Kyiv.

America’s support to Ukraine is not just about ammunition and weapons, from artillery shells to air defence systems. It also provides intelligence, training and other assistance that would be hard for Europeans to replace.

In the longer term, European leaders say any soldiers they send to Ukraine to defend a peace deal would need backup from their nuclear-armed superpower ally, even though Washington has made clear it will not deploy troops inside the country.

That would mean U.S. forces being ready to intervene to protect European troops if they came under attack from Russia.

"The Russians need to know that they're going to answer to the United States as well as to the Europeans on the ground," Mandelson told ABC News on Sunday.

Europe's reliance on the U.S. is even greater for its own defence inside the NATO alliance.

Tens of thousands of U.S. troops are deployed in bases across the continent and the U.S. provides a range of military capabilities that Europe currently can't match - from mid-air refuelling to a giant nuclear umbrella.

For now, Europeans are taking comfort in declarations by the Trump administration that it is committed to NATO. But they say NATO will have to change substantially - with a much greater European role.

"We know that they expect us to take greater responsibility for Europe’s security, and we must be ready for that," said a senior European official.

($1 = 0.9583 euros)

(Reporting by Andrew Gray and Lili Bayer; Additional reporting by John Irish; Writing by Andrew Gray; Editing by Peter Graff)