Michael Roman, a top official in former President Donald J. Trump’s 2020 campaign, is in discussions with the office of the special counsel Jack Smith that could soon lead to Mr. Roman voluntarily answering questions about a plan to create slates of pro-Trump electors in key swing states that were won by Joseph R. Biden Jr., according to a person familiar with the matter.

If Mr. Roman ends up giving the interview — known as a proffer — to prosecutors working for Mr. Smith, it would be the first known instance of cooperation by someone with direct knowledge of the so-called fake elector plan. That plan has long been at the center of Mr. Smith’s investigation into Mr. Trump’s wide-ranging efforts to overturn the 2020 election.

The talks with Mr. Roman, who served as Mr. Trump’s director of Election Day operations, were the latest indication that Mr. Smith is actively pressing forward with his election interference investigation even as attention has been focused on the other case in his portfolio: the recent indictment of Mr. Trump in Florida on charges of illegally keeping hold of classified documents and then obstructing the government’s repeated efforts to retrieve them.

In the past few weeks, several witnesses with connections to the fake elector plan have appeared in front of a grand jury in Federal District Court in Washington that is investigating the ways in which Mr. Trump and his allies sought to reverse his defeat to Mr. Biden. Among them was Gary Michael Brown, Mr. Roman’s onetime deputy, who was questioned in front of the grand jury on Thursday.

Mr. Roman did much of the legwork in putting together the fake elector plan and in finding ways to challenge Mr. Trump’s losses in several key battleground states, according to emails reviewed last summer by The New York Times. Mr. Roman, the emails show, coordinated with several other lawyers and aides to Mr. Trump in seeking to assemble support to create the false slates of electors in states like Georgia, Arizona, Michigan and Nevada.

Among those with whom Mr. Roman worked closely, the emails showed, were Boris Epshteyn, a lawyer and political adviser on the campaign who has since served as something like Mr. Trump in-house counsel, and Jenna Ellis, another lawyer who advised Mr. Trump after his defeat to Mr. Biden on how to challenge the election results.

In March, as part of a disciplinary proceeding by bar officials in her home state of Colorado, Ms. Ellis admitted that she had knowingly misrepresented facts in several of her public claims that widespread voting fraud had led to Mr. Trump’s defeat.

The emails reviewed by The Times showed Mr. Roman and others discussing options to try to prevent Mr. Biden from being certified as the winner of the election. He reported details of their activities to Rudolph W. Giuliani, Mr. Trump’s former personal lawyer, who championed Mr. Trump’s baseless claims of widespread election fraud.

The fake-elector strategy was arguably the longest-running and most expansive of the multiple efforts by Mr. Trump and his allies to overturn the results of the 2020 election. It involved a sprawling cast of pro-Trump lawyers, state Republican officials and White House aides in an effort that began even before some states had even finished counting their ballots.

The plan culminated in a campaign by Mr. Trump and others to pressure Vice President Mike Pence to use the false slates to subvert congressional certification of the outcome of the election in front of a joint session of Congress on Jan. 6, 2021. That proceeding was interrupted when a violent mob of Mr. Trump’s followers stormed the Capitol and chased lawmakers away.

Even some of those connected to efforts to keep Mr. Trump in office appeared to acknowledge the electors plan was legally dubious.

“We would just be sending in ‘fake’ electoral votes to Pence so that ‘someone’ in Congress can make an objection when they start counting votes, and start arguing that the ‘fake’ votes should be counted,” Jack Wilenchik, a Phoenix-based lawyer who was helping to organize the pro-Trump electors in Arizona, wrote in a December 2020 email to Mr. Epshteyn.

In a follow-up email, Mr. Wilenchik wrote that calling them “alternate” electors was probably better than “fake” electors, adding a smiley face emoji.

The F.B.I. formally opened an investigation into the fake elector plan in April 2022, according to people familiar with the matter, and federal prosecutors issued a flurry of grand jury subpoenas to Republican officials in states like Georgia, Arizona, Michigan and Nevada two months later.

Two top Republican officials from Nevada who were involved in the plan — Jim DeGraffenreid and Michael McDonald — gave testimony to the grand jury in Washington two weeks ago, on the same day that Mr. Trump was arraigned in Miami in the classified documents case.

Throughout the winter and into the spring, a steady stream of witnesses — some of them exceptionally close to Mr. Trump — were subpoenaed to appear in front of the grand jury and answer questions about the fake-elector plan and other efforts by the former president to cling to power after the losing the election.

Among those who were forced to show up were Pat A. Cipollone, Mr. Trump’s former White House counsel; Mark Meadows, his onetime chief of staff; and former Vice President Mike Pence. Most of these witnesses sought to limit the scope of their testimony by asserting various forms of privilege in a long-running, closed-door legal battle that ultimately failed.

In a separate avenue of inquiry, the Justice Department seized the cellphones of a handful of lawyers connected to the fake elector scheme in June 2022. Those included John Eastman, a California law professor who advised Mr. Trump on the plan, and Jeffrey Clark, a former Justice Department official who was nearly installed as acting attorney general and who helped to draft a letter to state officials in Georgia recommending that they create a slate of pro-Trump electors.

By last July, the Justice Department had created a team of prosecutors — working under the code name Project Coconut — to sort through the various communications seized from Mr. Eastman, Mr. Clark and another former Justice Department lawyer, Ken Klukowski, for any that were potentially protected by attorney-client or executive privilege, according to a person familiar with the matter.

This so-called filter team grew in size and scope, the person said, as investigators obtained more data from other subjects of the inquiry, including Mr. Meadows; Cleta Mitchell, a lawyer who recruited Mr. Eastman to work on the fake-elector plan; and Mr. Epshteyn.

Adam Goldman contributed reporting.