Asked repeatedly why he had been sent to testify rather than Mr. Gulati, who sits on FIFA’s governing executive committee and has long associations with several of the indicted officials, Mr. Flynn said it was at the advice of an outside lawyer, and because he had greater familiarity with U.S. Soccer’s daily operations than Mr. Gulati does.

Staunchly defending his organization’s integrity, Mr. Flynn invoked FIFA’s recent presidential election as an example in which U.S. Soccer had taken a principled stand. Sepp Blatter, the longtime FIFA president, won a majority vote days after his close associates were arrested; in that election, U.S. Soccer supported Mr. Blatter’s challenger, Prince Ali bin al-Hussein of Jordan.

“We did so notwithstanding the potential political risks, including the potential impact on our possible bid to host the 2026 Men’s World Cup,” Mr. Flynn said. But he failed to note that U.S. Soccer had supported Mr. Blatter when he ran unopposed in his previous election, in 2011, in a vote that took place under the cloud of an earlier corruption scandal. (More than a dozen countries abstained in that vote, in which Mr. Blatter received 186 of the 203 votes.)

Mr. Blatter, too, was invited to testify on Wednesday by Mr. Moran’s office but declined to appear. He has not been accused of a crime in the current scandal, though investigators have said he is under continued scrutiny. Mr. Blatter’s lawyer, Richard Cullen, did not respond to request for comment on why Mr. Blatter chose not to attend the hearing.

U.S. Soccer is one of the 209 member associations that belong to FIFA, but it is also a member of Concacaf, a regional confederation within FIFA that oversees the federations in North America, Central America and the Caribbean. The recent charges brought by the United States centered on criminal activity within Concacaf, which is headquartered in Miami.

On Wednesday, Mr. Flynn lauded Concacaf’s recently proposed reforms, including term limits for executives and public disclosures of their pay, as a sign of change. He called those proposed changes “sweeping” and suggested they would make a strong framework for FIFA to use as it seeks to reinvent itself.

But witnesses and senators alike questioned whether such reforms — many of which have yet to be enacted — were possible before determining how much knowledge the current FIFA leadership had of decades of criminal activity.