WASHINGTON - U.S. diplomat Gordon Sondland has told two different stories to lawmakers leading the impeachment inquiry against President Donald Trump. On Wednesday, he is certain to face sharp questions about which one is right.

The wealthy hotel entrepreneur who serves as U.S. ambassador to the European Union could be the most crucial witness yet in a week of televised hearings that have laid bare the misgivings of U.S. officials about Trump's dealings in Ukraine.

Sondland was a central player in the president's informal campaign to get Ukraine to investigate political rival Joe Biden, a leading Democratic candidate in the 2020 presidential election. He says he did not initially realize that the former vice president was a target.

Unlike some other figures close to Trump, Sondland has cooperated with the impeachment investigation. But Sondland's story has not been consistent and has differed in some respects from the accounts of other witnesses.

Sondland told lawmakers in closed-door testimony last month that he saw no link between Trump's investigation request and the White House's decision to temporarily withhold $391 million in security aid to Ukraine.

Weeks later, Sondland updated his story in supplemental testimony, telling lawmakers he had remembered that he had told Ukraine President Volodymyr Zelenskiy's administration that it would likely not get the money unless it publicly committed to taking action.

Sondland also did not initially tell lawmakers about a July 26 phone call that another witness said he conducted with Trump on a mobile phone in a Kiev restaurant that is certain to be a prominent subject in Wednesday's hearing.

According to U.S. embassy staffer David Holmes, Sondland told Trump during that call that Zelenskiy would conduct the investigation he sought. After hanging up, according to Holmes, Sondland said that Trump only cared about "big stuff" like the "Biden investigation."

Holmes is scheduled to testify on Thursday.

Kurt Volker, a former diplomat who worked with Sondland on the Ukraine negotiations, said in testimony to lawmakers on Tuesday: "Ambassador Sondland is a big personality and sometimes he says things that might be a bit bigger than life."

Volker and Sondland, along with outgoing U.S. Energy Secretary Rick Perry, were known as the "three amigos" handling Trump's unofficial channel to Ukrainian government officials.

But Sondland's testimony could also raise new questions about their coordination with official channels. The New York Times, citing two unnamed sources, on Wednesday reported Sondland kept U.S. Secretary of State Michael Pompeo updated on efforts to pressure Kiev to publicly commit to Trump's investigations.

Pompeo has declined to cooperate with House investigators even as a number of State Department officials have testified. Perry has also refused to cooperate.

"At this point, we have a lot of questions for him," U.S. Representative Raja Krishnamoorthi, a Democrat on House Intelligence Committee leading the inquiry, told MSNBC in an interview on Wednesday.

The panel's hearings could eventually lead to articles of impeachment being voted on by the Democratic-controlled House of Representatives.

The effort is, however, unlikely to force Trump from office, as the Republican-controlled Senate would have to vote to convict him by a two-thirds margin - a prospect that Senate Republican Leader Mitch McConnell dismissed as "inconceivable" on Tuesday.

Trump has denied wrongdoing, called the inquiry a witch hunt and assailed some of the witnesses.

Sondland was tapped as Trump's envoy after he donated $1 million to the president's inauguration. In October, Trump called him "a really good man," but after Sondland's amended statement to House investigators this month he told reporters at the White House: "I hardly know the gentleman."

According to Reuters/Ipsos polling, 46 percent of Americans support impeachment, while 41 percent oppose it.

(Reporting by Andy Sullivan; additional reporting by Doina Chiacu Editing by Sonya Hepinstall and Steve Orlofsky) ((andy.sullivan@thomsonreuters.com; +1 202 354 5864; Reuters Messaging: @andysullivan))