Anthony Ornato, a Key Jan. 6 Witness, to Speak With House Panel

WASHINGTON — Anthony M. Ornato, the former Secret Service agent and White House aide at the heart of a dispute over conflicting accounts of President Donald J. Trump’s actions during the Jan. 6 Capitol riot, is scheduled to interview on Tuesday before the House committee investigating the attack, according to two people familiar with the matter.

The committee has sought for weeks to re-interview Mr. Ornato as it digs deeper into the activities of the Secret Service around the time of Jan. 6, 2021, an area of inquiry that members believe is one of the most important final pieces of unfinished business before the panel completes its much-anticipated report into the attack.

Mr. Ornato, who as deputy White House chief of staff oversaw the logistics of the president’s movements outside, is key to a dispute over the events in a presidential S.U.V. that day. Cassidy Hutchinson, a former White House aide, testified to lawmakers that Mr. Ornato told her that Mr. Trump became enraged and demanded to join a crowd of his supporters at the Capitol.

Secret Service officials have challenged some aspects of her account, and members of the panel have accused Mr. Ornato of being less than honest with them during a previous interview. Significant new answers from Mr. Ornato could help determine whether the dispute is a legitimate battle over the credibility of Ms. Hutchinson or an attempt to muddy the waters over her testimony, which provided a devastating account of Mr. Trump’s actions on Jan. 6.

Mr. Ornato’s closed-door interview is scheduled a day after the panel questioned Kellyanne Conway, a former senior adviser to Mr. Trump. Committee members were interested in a scene from the book “The Big Lie” by Jonathan Lemire in which Mr. Trump, using an expletive, asked Ms. Conway how he could lose to President Biden.

The panel is compiling more evidence of how Mr. Trump knew his claims of a stolen election were false as members discuss how best to present the findings from their more than 1,000 witness interviews in a final report expected to be hundreds of pages long. Lawmakers have also said they plan to release the full transcripts of their interviews.

In recent weeks, the Jan. 6 committee has interviewed several Secret Service officials, including Robert Engel, who was the lead Secret Service agent for Mr. Trump on Jan. 6, 2021, as well as the driver of the president’s vehicle in the motorcade.

“We learned some additional information, and at some point we plan to use it,” Representative Bennie Thompson, Democrat of Mississippi and the chairman of the committee, said of Mr. Engel’s testimony.

In her public testimony, Ms. Hutchinson said she learned from Mr. Ornato of a stunning scene in the back of the presidential vehicle on Jan. 6, shortly after a speech by Mr. Trump at the Ellipse outside the White House. She testified that Mr. Ornato told her that Mr. Trump tried to force the Secret Service to drive him to the Capitol to join his supporters. In her recounting, Mr. Ornato said Mr. Trump tried to grab the steering wheel of the armored vehicle.

Ms. Hutchinson also said Mr. Ornato told her the president “lunged” at Mr. Engel. Mr. Engel, Ms. Hutchinson testified, was present as Mr. Ornato related the story to her and did not correct Mr. Ornato’s account.

Secret Service officials have said Mr. Ornato, Mr. Engel and the driver of the vehicle are prepared to testify that some details in that account are incorrect. The officials do not dispute that Mr. Trump angrily demanded to be taken to the Capitol, but they deny there was a physical altercation.

Committee members have argued they would know little about Mr. Trump’s actions in the S.U.V. without Ms. Hutchinson’s testimony. Representative Adam Kinzinger, Republican of Illinois and a member of the committee, wrote on Twitter in June, “There seems to be a major thread here… Tony Ornato likes to lie.”

The committee has obtained more than 1.5 million pages of documents and communications from the Secret Service in response to a subpoena. The communications lay out how Secret Service personnel tried to find a route to take Mr. Trump to the Capitol in the S.U.V. and how those plans were ultimately rebuffed amid the chaos.

The Secret Service staff initially tried to accommodate Mr. Trump’s wishes, but supervisors at the agency expressed alarm, and the District of Columbia police declined to block off intersections for his motorcade as a mob of his supporters began attacking and injuring dozens of police officers, according to the communications, which were described by two people familiar with their contents.

Mr. Engel broke the news to Mr. Trump inside the vehicle, prompting an angry outburst. Afterward, a Secret Service supervisor followed up to ensure that Mr. Trump would not be joining the mob at the Capitol, the communications show.

Mr. Thompson said the panel is finished with eight chapters of its report, which is likely to be issued in December and is the subject of much internal debate over how much to focus on Mr. Trump’s actions versus security failures at the Capitol.

A subcommittee of four lawyers on the committee — Liz Cheney, Republican of Wyoming; Jamie Raskin, Democrat of Maryland; Zoe Lofgren, Democrat of California; and Adam B. Schiff, Democrat of California — also is studying the issue of whether to issue criminal referrals to the Justice Department for Mr. Trump and some of his top allies.