WASHINGTON — The House committee investigating the Jan. 6 attack on the Capitol issued a subpoena on Wednesday to Peter Navarro, a White House adviser to former President Donald J. Trump who was involved in what he called an “operation” to keep Mr. Trump in office after he lost the 2020 election.

The subpoena was the committee’s latest attempt to obtain information about efforts underway in Mr. Trump’s White House to invalidate the election. In his book, titled “In Trump Time,” and in interviews with The New York Times and other outlets, Mr. Navarro has said that he worked with Stephen K. Bannon and other allies of Mr. Trump to develop and carry out a plan to delay Congress’s formal count of the 2020 presidential election results to buy time to change the outcome.

Representative Bennie Thompson, Democrat of Mississippi and the chairman of the committee, highlighted how openly and proudly Mr. Navarro has discussed those machinations, saying he “hasn’t been shy about his role in efforts to overturn the results of the 2020 election, and has even discussed the former president’s support for those plans.”

Mr. Navarro has insisted that the violence at the Capitol on Jan. 6 was not part of his plans, which he said included having Vice President Mike Pence reject electors for Joseph R. Biden Jr. when Congress met in a joint session to formally count them.

“To pull off an operation Bannon has dubbed the Green Bay Sweep — and thereby keep President Trump in the White House for a second term — we must have only peace and calm,” Mr. Navarro wrote in his book.

He said the idea was for Mr. Pence to be the “quarterback” of the plan and “put certification of the election on ice for at least another several weeks while Congress and the various state legislatures involved investigate all of the fraud and election irregularities.”

There has been no evidence of widespread fraud or irregularities in the 2020 election, though Mr. Trump continues to claim that it was “stolen” from him.

Mr. Navarro also wrote a 36-page report alleging election fraud as part of what he called an “Immaculate Deception.” In an interview with The Times, he said he relied on “thousands of affidavits” from Mr. Trump’s personal lawyer, Rudolph W. Giuliani, and Bernard B. Kerik, the former New York police commissioner, to help produce the report, which claimed there “may well have been a coordinated strategy to effectively stack the election deck against the Trump-Pence ticket.”

The Jan. 6 committee described the claims in Mr. Navarro’s report as having been “discredited in public reporting, by state officials and courts.”

Mr. Navarro said that he made sure Republican members of Congress received a copy of his report and that more than 100 members of Congress had signed onto the plans. (Ultimately, 147 Republican members of Congress objected to certifying at least one state for Mr. Biden.)

“My role was very specific in the Green Bay Packers sweep,” he said in an interview. “I was the analytical guy who provided the receipts, as Bannon calls it. When the hearings were held and the congressmen were having the debate over the results, they’d have my report in their hands.”

“I tried repeatedly to get to Pence,” Mr. Navarro said, “and I couldn’t do it. I was locked out.”

An aide to Mr. Navarro was also in contact with a group of Trump allies who were pushing for the former president to order the seizure of voting machines.

When the former national security adviser Michael T. Flynn and the lawyer Sidney Powell arrived at the White House on Dec. 18 to press Mr. Trump to pursue their plan, they were escorted in by Garrett Ziegler, a young aide to Mr. Navarro, according to Mr. Ziegler’s account.

Mr. Ziegler’s credentials were revoked after the incident.

Mr. Navarro is currently defying a subpoena from another congressional investigation. He is refusing to cooperate with a subpoena from the House Select Subcommittee on the Coronavirus Crisis.

He said Wednesday he would respond to the Jan. 6 committee’s subpoena shortly.

More than 500 witnesses have cooperated with the Jan. 6 inquiry so far.