WASHINGTON — Partisan tensions between the leaders of the House committee investigating the 2012 attacks in Benghazi, Libya, erupted on Sunday, just four days before Hillary Rodham Clinton is scheduled to testify at a public hearing of the panel.

As the committee’s chairman, Representative Trey Gowdy, Republican of South Carolina, prepared to go on television to provide his latest defense of the investigation, the committee’s top Democrat, Representative Elijah E. Cummings of Maryland, released information undercutting one of Mr. Gowdy’s recent allegations about Mrs. Clinton’s use of her private email when she was secretary of state.

Mr. Gowdy had claimed this month that messages sent and received by Mrs. Clinton included the name of a Central Intelligence Agency source in Libya. That information was “some of the most protected information in our intelligence community,” Mr. Gowdy said. The fact that Mrs. Clinton sent and received these materials, he said, debunked her “claim that she never sent any classified information from her private email address.”

But Mr. Cummings said on Sunday that the C.I.A. had informed the committee that information about the source was not classified.