WASHINGTON — The House committee investigating the Jan. 6 attack on the Capitol is seeking testimony and documents from Representative Scott Perry of Pennsylvania, the first public step the panel has taken to try to get information from any of the Republican members of Congress deeply involved in President Donald J. Trump’s effort to stay in power.

The committee sent a letter on Monday to Mr. Perry, the incoming chairman of the ultraconservative House Freedom Caucus, asking for him to meet with its investigators and voluntarily turn over his communications during the buildup to the riot.

To date, the panel has been reluctant to issue subpoenas for information from sitting members of Congress, citing the deference and respect lawmakers in the chamber are supposed to show one another. But Representative Bennie Thompson, Democrat of Mississippi and the chairman of the panel, has pledged to take such a step if needed.

“The select committee has tremendous respect for the prerogatives of Congress and the privacy of its members,” Mr. Thompson said in his letter to Mr. Perry. “At the same time, we have a solemn responsibility to investigate fully all of these facts and circumstances.”

A spokesman for Mr. Perry did not immediately respond to a request for comment.

In the weeks after the 2020 election, Mr. Perry, a member of Congress since 2013, compiled a dossier of voter fraud allegations and coordinated a plan to try to replace the acting attorney general, who was resisting Mr. Trump’s attempts to overturn the election, with a more compliant official.

A former Army helicopter pilot whose colleagues call him General Perry, Mr. Perry introduced Mr. Trump to Jeffrey Clark, the acting head of the Justice Department’s civil division who became one of the Stop the Steal movement’s most ardent supporters. Around this time, the committee said, investigators believe Mr. Perry was communicating with Mark Meadows, who was then the White House chief of staff, via an encrypted app, Signal.

Mr. Clark has said he will invoke his Fifth Amendment right against self-incrimination when he next appears before the panel.

“We have received evidence from multiple witnesses that you had an important role in the efforts to install Mr. Clark as acting attorney general,” Mr. Thompson wrote to Mr. Perry. “When Mr. Clark decided to invoke his Fifth Amendment rights, he understood that we planned to pose questions addressing his interactions with you, among a host of other topics.”

Shortly after Mr. Trump lost the election, Mr. Perry joined Representative Jim Jordan, Republican of Ohio, as they huddled with senior White House officials at Trump campaign headquarters in Arlington County, Va., and came up with a strategy that would become a blueprint for Mr. Trump’s supporters in Congress: hammer home the idea that the election was tainted, announce legal actions being taken by the campaign and bolster the case with allegations of fraud.

Mr. Perry pressed the case for weeks, and in January circulated a letter written by Pennsylvania state legislators to Senator Mitch McConnell of Kentucky and Representative Kevin McCarthy of California, the top Republicans in each chamber, asking Congress to delay certification. “I’m obliged to concur,” Mr. Perry wrote.

The committee also said it wanted to ask Mr. Perry about discussions he was involved in regarding allegations that voting machines had been corrupted.

The panel asked him to turn over all “relevant electronic or other communications” related to the buildup to Jan. 6, including his communications with Mr. Trump and his legal team as well as others involved in planning rallies on Jan. 6 and the objections in Congress to Joseph R. Biden Jr.’s victory.

The panel proposed meeting with Mr. Perry between Christmas and New Year’s or in the first full week of January.

The move to seek information from Mr. Perry comes as the House is planning how best to commemorate the horrors of Jan. 6, when the pro-Trump mob that stormed the Capitol injured dozens of police officers in a rampage that left several dead. More than 700 defendants have been charged in connection with the siege.

Speaker Nancy Pelosi, Democrat of California, said on Monday that the anniversary of the attack next month would be a day of “solemn observance.”

“Already, preparations are underway for a full program of events, including a discussion among historians about the narrative of that day; an opportunity for members to share their experiences and reflections from that day; and a prayerful vigil in the evening,” Ms. Pelosi wrote in a letter to fellow lawmakers on Monday.