The Senate Judiciary Committee issued a subpoena to the Justice Department on Wednesday for White House political adviser Karl Rove’s e-mail regarding the firing of eight U.S. attorneys.

Chairman Patrick J. Leahy, D-Vt., signed the subpoena to Attorney General Alberto R. Gonzales. It directs the Justice Department to produce by May 15 any e-mail messages “to, from or copied” to Rove about the firings, whether on White House, Republican National Committee or other accounts.

“I continue to hope that the Department will cooperate with the committee’s investigation, but it is troubling that significant documents highly relevant to the Committee’s inquiry have not been produced,” Leahy wrote in his letter to Gonzales.

Fred F. Fielding, the White House counsel, had offered to provide such e-mail messages between Rove and people outside the White House as part of a broader deal regarding the terms of interviews with Rove and other White House officials. But negotiations have remained stalled between the Judiciary committees and the White House, which has refused to agree to transcripts of any closed-door interviews.

Rove is also a central figure in an inquiry by the House Oversight and Government Reform Committee, which is investigating allegations that the White House political-affairs shop used federal resources to make campaign-related presentations to officials at federal agencies.

Chairman Henry A. Waxman, D-Calif., has also subpoenaed Republican National Committee documents, as well as the testimony of RNC Chairman Mike Duncan, in his probe of the use of private e-mail accounts by White House officials. Waxman contends that the e-mail accounts might have been used to circumvent presidential record-keeping laws.

Also on Wednesday, six members of the Senate Judiciary Committee signed a letter to Gonzales asking him to provide a copy of a March 2006 order delegating authority over the hiring and firing of most Justice Department political employees to former chief of staff Kyle Sampson and former White House liaison Monica Goodling.

“The order appears to be responsive to the committee’s requests insofar as it dealt with the appointment and removal of inferior officers who are not subject to Senate confirmation, which would include interim and acting U.S. attorneys,” stated the letter, which was signed by three Democrats and three Republicans.

The House Judiciary Committee on Wednesday released written responses to questions posed by the panel to six of the fired U.S. attorneys.

Two, John McKay of Washington state and Paul Charlton of Arizona, said they interpreted January calls from Michael Elston, the former chief of staff to Deputy Attorney General Paul J. McNulty, as threatening.

“I greatly resented what I felt Mr. Elston was trying to do: buy my silence by promising that the attorney general would not demean me in his Senate testimony,” wrote Elston, referring to Gonzales’ Jan. 18 appearance before the Senate Judiciary Committee. “I believed Mr. Elston’s tone was sinister and that he was prepared to threaten me further if he concluded I did not intend to continue to remain silent about my dismissal.”

Similarly, Charlton wrote, “In that conversation I believe that Elston was offering me a quid pro quo agreement: my silence in exchange for the attorney general’s.”

On Thursday, James B. Comey, the former deputy attorney general, is scheduled to testify before the House Judiciary Commercial and Administrative Law Subcommittee.

Jonathan Allen contributed to this story.