MADRID/BERLIN/ROME (Reuters) - Europe's leaders defended U.S. President Joe Biden after a number of gaffes during a NATO summit while the continent's media took them as further evidence he was not fit to defeat Donald Trump in November's presidential election.

Biden, 81, drew gasps at the gathering in Washington when he introduced Ukrainian President Volodymyr Zelenskiy as "President Putin" before mixing up the names of his vice president, Kamala Harris and Trump during a press conference that his aides had arranged to shore up public trust in his mental faculties.

Biden has faced calls from fellow Democrats and supporters to drop his re-election campaign after a sometimes incoherent performance against Trump in a televised June 27 debate crystallised concerns about his ability to win the Nov. 5 vote and handle the demands of the White House.

While European leaders who attended the summit were diplomatic about Biden and praised the organisation of the summit, the European press, such as Britain's Daily Telegraph, concluded that "Biden looks finished".

"Slips of tongue happen, and if you always monitor everyone, you will find enough of them," German Chancellor Olaf Scholz said when asked by reporters about Biden confusing Zelenskiy with Putin.

Newly elected British Prime Minister Keir Starmer, speaking before Biden's gaffes, said he and the president were able to address a number of issues "at pace" during their first meeting.

"He was actually on really good form, and mentally agile - absolutely across all the detail," Starmer told the BBC in an interview.

Spanish Prime Minister Pedro Sanchez said Biden looked "well" and that he attended all summit sessions, unlike other leaders. Italian Prime Minister Giorgia Meloni was less effusive but praised Biden's organisation of "a very good summit".

Other European politicians were less forgiving.

Geert Wilders, whose far-right party won the Netherlands' last election, made fun of Biden, posting a photo of Zelenskiy and Harris on X under the title: "President Putin meets Vice President Trump."

Ukrainians queried by Reuters were mainly sympathetic to Biden for his mix-up of Zelenskiy with Putin.

"I think he was just tired," Yevhen, a 33-year-old IT specialist in Kyiv who declined to give his surname, said.

But he also worried that such gaffes "could have certain consequences for Ukraine" - given concerns about how Trump, if elected, would treat NATO and Russia's invasion of Ukraine - if the U.S. public stopped trusting Biden

A post-summit press conference failed to convince European media that Biden can rebuild confidence in his mental acuity.

"This was Joe Biden's chance to win over doubters. He blew it," said a Times of London headline, while Italy's Il Giornale concluded it was the "end of the road for Biden".

Germany's Frankfurter Allgemeine Zeitung described Biden's closing press conference as a "humiliation ... To put it harshly: The dignity of the office holder has been irreversibly tarnished."

Britain's Guardian newspaper agreed, describing the press conference as "painful to watch" and "politics as bloodsport".

Switzerland's Neue Zuercher Zeitung daily concluded that the only chance the Democrats had of defeating the Republican Trump in November was for Biden to withdraw from the race.

"An old man flexing his political muscles and raising his brittle voice does not come across as powerful...This president is not fit for a second term," the Zurich newspaper wrote.

(Reporting by Charlie Devereux, Kirsti Kolle, Crispian Balmer, Belen Carreño and Charlotte Van Campenhout; writing by Charlie Devereux; editing by Mark Heinrich)