President Trump said Thursday that he trusted President Vladimir V. Putin of Russia not to violate the terms of a potential peace deal with Ukraine, even as he refused to pledge U.S. military support for a peacekeeping force.

“I think he’ll keep his word,” Mr. Trump said of Mr. Putin as he hosted Britain’s prime minister, Keir Starmer, at the White House.

Of Mr. Putin, the president said, “I’ve known him for a long time now.”

Mr. Trump’s comments underscored his embrace of Mr. Putin just a day before Ukraine’s president, Volodymyr Zelensky, is scheduled to arrive in Washington to finalize a deal to share revenue from mineral sources with the United States. Mr. Trump has pushed for access to Ukraine’s minerals to make up for billions of dollars in military and humanitarian aid the United States has delivered to Ukraine over three years.

In the opening weeks of his presidency, Mr. Trump has ended the diplomatic isolation of Russia, falsely accused Ukraine of starting the war with Russia and repeatedly disparaged Mr. Zelensky, including by calling him a “dictator.” He appeared to change his tune on Thursday, however, predicting that the two of them would have a good in-person meeting.

“I have a lot of respect for him,” Mr. Trump said, although he dodged a question about whether he would apologize to Mr. Zelensky on Friday for the “dictator” comment.