WASHINGTON — President Trump unleashed a series of falsehoods on Friday in an effort to invalidate the impeachment inquiry and counter sworn testimony from officials in his own administration, after a week of damaging public hearings.

In a 53-minute phone interview with “Fox & Friends,” Mr. Trump accused David Holmes, a political counselor to the top American diplomat in Ukraine, of fabricating a phone call between Mr. Trump and the ambassador to the European Union. Mr. Holmes told impeachment investigators that he had overheard the president asking the ambassador, Gordon D. Sondland, about Ukrainian investigations into his political rivals, a consequential detail in the Democrats’ impeachment inquiry.

“I guarantee you that never took place,” Mr. Trump said. He added that he barely knew Mr. Sondland, a wealthy hotelier from Oregon who contributed $1 million to Mr. Trump’s inaugural committee. In his own testimony under oath, Mr. Sondland corroborated Mr. Holmes’s account.

The interview on Friday, broadcast live and commercial-free with a view of the “Fox & Friends” hosts speaking by phone to Mr. Trump, gave the president a chance to respond to the damaging revelations of the past week and reprise widely debunked theories and some of his favorite lines of attack.