Washington — Washington -- The House Judiciary Committee sharply broadened its investigation yesterday into the firing of eight top federal prosecutors, calling on the White House to provide legal documents and make current and former senior officials available for interviews -- including former White House Counsel Harriet E. Miers. The Democratic-controlled panel is investigating whether the wave of firings in December may have been part of a political vendetta against prosecutors who did not bring criminal cases that would have hurt Democratic candidates in last year's midterm election. There is also concern that Washington officials might have imposed political or ideological litmus tests on prosecutorial decisions. Specifically, the committee is requesting interviews with Miers and Deputy Counsel William Kelly, and is asking the administration "to produce relevant documents, including White House communications on the firings with the Justice Department and members of Congress." Two of the dismissed prosecutors -- David C. Iglesias of Albuquerque, N.M., and John McKay of Seattle -- told the committee this week of phone calls from Republican lawmakers inquiring about possible investigations into Democratic activities at the time of the November election. Another fired U.S. attorney, H.E. "Bud" Cummins III of Little Rock, Ark., said he was told by Washington that he was being moved out to make room for Timothy Griffin, a Republican operative for chief White House political adviser Karl Rove. Rep. John Conyers Jr., a Michigan Democrat and the committee chairman, said Democrats believe that the Justice Department has given conflicting reasons for the terminations, and that the committee wants to "get a clear and credible answer from the Bush administration on who made the decision to fire these U.S. attorneys and why they did it." "We went to make sure that those who would contaminate our justice system with partisan politics are held accountable," Conyers said. Tony Fratto, a spokesman at the White House, said the administration will review the committee's request. "I'm not in a position to comment on how we will address it," he said. "But we certainly will respond." Conyers' query was sent to current White House Counsel Fred F. Fielding, and the unusual step could set up a confrontation between the two branches of government. The Bush White House has often taken a tough stance on protecting the confidentiality of internal legal documents and its decision-making process. "It poses a tricky question," said Carl Tobias, a University of Richmond law school professor. "Miers has left. And my sense is that Fred Fielding is a real expert on this type of issue and will attempt to craft a reasonable compromise rather than fight Congress." Fielding has more than three decades of experience with the legal relationship between presidents and Congress. He served in the White House counsel's office during Richard M. Nixon's presidency and Watergate; he was also White House counsel under President Ronald Reagan. In Conyers' letter to Fielding, he mentioned one of the areas that committee members want to explore, pointing out McKay's testimony this week that Miers personally told him he had "mishandled" a situation in Washington state by not investigating voter fraud in last year's gubernatorial race. "This testimony raises serious issues concerning possible undue influence and obstruction of justice," Conyers said. Richard A. Serrano writes for the Los Angeles Times.