WASHINGTON — Former Utah-based attorney and Brigham Young University graduate D. Kyle Sampson resigned Monday as chief of staff to Attorney General Alberto Gonzales in the midst of a growing scandal involving eight fired U.S. attorneys.

Sampson, who almost became Utah's U.S. attorney, had a federal political career that included stops in the U.S. Congress, the White House and the Justice Department.

Democrats in the House and Senate plan for hearings and investigations into what really led to the firings of the U.S. attorneys and who were the major players.

Justice Department officials have testified before Congress that decisions to fire the attorneys were based on the individual attorneys' job performances without any input from the White House.

But documents released by the Justice Department to the House Judiciary Committee show Sampson had multiple e-mail conversations with White House counsel Harriet Miers and other officials in deciding — and sometimes listing — which attorneys should go.

Gonzales dismissed calls for his resignation at a press conference Tuesday but admitted that "mistakes were made" and will be corrected so they will not happen again.

"Obviously, I am concerned about the fact that information — incomplete information — was communicated or may have been communicated to the Congress," Gonzales said.

Upon his resignation, Sampson admitted he did not tell his bosses about the extent of his many discussions with the White House about removing the prosecutors, which led to incomplete testimony before Congress.

A call to Sampson's cell phone Tuesday was not returned.

Sampson advised the White House that "there are practical obstacles" to following a proposed plan to fire all 93 U.S. attorneys. That comment was made in a Jan. 9, 2006, e-mail marked as "treat as confidential" and sent to Miers and Bill Kelley, another White House official.

In the e-mail, Sampson said the proposed firings "would cause significant disruption to the work of the Department of Justice." Among other reasons, he said it would be hard to find suitable replacements quickly and have the Senate confirm the replacements fast enough. He said none of the obstacles "are insuperable" but that "a limited number of U.S. attorneys could be targeted for removal and replacement, mitigating the shock to the system that would result from an across-the-board firing."