WASHINGTON — The House committee investigating the Jan. 6 attack on the Capitol on Tuesday subpoenaed Rudolph W. Giuliani and the legal team that pursued a set of conspiracy-filled lawsuits on behalf of former President Donald J. Trump that made claims of fraud in the 2020 presidential election.

In addition to Mr. Giuliani, Mr. Trump’s personal lawyer and a ringleader of the group, the panel subpoenaed three others: Jenna Ellis, who drafted a memo on how Mr. Trump could overturn the election by exploiting an obscure law; Sidney Powell, a lawyer whose organization raised millions of dollars based on false claims that election machines were rigged; and Boris Epshteyn, who pursued allegations of election fraud in Nevada and Arizona and participated in a call with Mr. Trump on the morning of Jan. 6, “during which options were discussed to delay the certification of election results,” the committee said.

“The four individuals we’ve subpoenaed today advanced unsupported theories about election fraud, pushed efforts to overturn the election results or were in direct contact with the former president about attempts to stop the counting of electoral votes,” Representative Bennie Thompson, Democrat of Mississippi and the chairman of the committee, said in a statement.

On Jan. 6, speaking to a crowd of Trump supporters before the attack on the Capitol, Mr. Giuliani called for “trial by combat.” Later, as the building was under siege, he called lawmakers in an attempt to delay the certification of Joseph R. Biden Jr.’s victory.