By PHILIP SHENON and ELISABETH BUMILLER
WASHINGTON, Jan. 26 — The investigation of Jack Abramoff, the disgraced Republican lobbyist, took a surprising new turn on Thursday when the Justice Department said the chief prosecutor in the inquiry would step down next week because he had been nominated to a federal judgeship by President Bush.
The prosecutor, Noel L. Hillman, is chief of the department's public integrity division, and the move ends his involvement in an inquiry that has reached into the administration as well as the top ranks of the Republican leadership on Capitol Hill.
The administration said that the appointment was routine and that it would not affect the investigation, but Democrats swiftly questioned the timing of the move and called for a special prosecutor.
The announcement came as Mr. Bush faced a barrage of questions about why he would not make public "grip-and-grin" photographs of him with Mr. Abramoff. The photographs apparently show Mr. Bush and Mr. Abramoff smiling at White House Hanukkah parties and Republican fund-raising receptions.
Mr. Bush's position, which he offered at a news conference on Thursday morning that was peppered with questions about Mr. Abramoff, was that the photographs were so common as to be almost meaningless and that it was part of his job "to shake hands with people and smile." He said he could not remember posing for the pictures, or, for that matter, even meeting Mr. Abramoff.
"I had my picture taken with him, evidently," Mr. Bush said. "I've had my picture taken with a lot of people. Having my picture taken with someone doesn't mean that I'm a friend with them or know them very well."
He said, "I'm also mindful that we live in a world in which those pictures will be used for pure political purposes, and they're not relevant to the investigation."
The White House, which announced Mr. Bush's selection of Mr. Hillman for the court in a routine e-mail message on Wednesday that included 15 other nominations to judgeships and federal jobs, dismissed the calls for a special prosecutor.
"It's nothing but pure politics," said Scott McClellan, the White House press secretary. "The Justice Department is holding Mr. Abramoff to account, and the career Justice prosecutors are continuing to fully investigate the matter."
A special prosecutor would not be especially welcome at the White House. Patrick J. Fitzgerald, the special counsel in the C.I.A. leak case, is more than two years into an investigation that has resulted in the indictment of a top vice-presidential aide, I. Lewis Libby Jr., and has left Karl Rove, the president's chief political adviser, under investigation.
Mr. Hillman's departure from the Justice Department creates a vacancy at the top of the Abramoff inquiry only three weeks after Mr. Abramoff, once one of the city's most powerful Republican lobbyists and a major fund-raiser for Mr. Bush, announced his guilty plea and agreed to testify against others, possibly including members of Congress.
A former senior White House budget official, David H. Safavian, has been indicted in the case on charges of lying about his contacts with Mr. Abramoff, a former lobbying partner. The Justice Department's plea agreement with Mr. Abramoff makes clear that prosecutors are investigating several members of Congress and other public officials who are suspected of having accepted gifts from the lobbyist in exchange for official acts.
Colleagues at the Justice Department say Mr. Hillman has been involved in day-to-day management of the Abramoff investigation since it began almost two year ago. The inquiry, which initially focused on accusations that Mr. Abramoff defrauded Indian tribes out of tens of millions of dollars in lobbying fees, is being described within the department as the most important federal corruption investigation in a generation.
Mr. Hillman's nomination for a judgeship was among the factors cited Thursday by four Democratic lawmakers, two senators and two representatives, in calling on Attorney General Alberto R. Gonzales to name a special prosecutor to oversee the corruption investigation.
The timing of Mr. Hillman's nomination "jaundices this whole process," Senator Charles E. Schumer, Democrat of New York, said in an interview. "They have to appoint a special counsel. I think there will be broad support for one."
Representative George Miller, Democrat of California, called the timing "startling" and said, "You have one of the chief prosecutors removed from a case that has tentacles throughout the Republican leadership of Congress, throughout the various agencies and into the White House."
White House officials have said that Mr. Abramoff had no improper dealings with the White House. They have said he attended "staff level" meetings at the White House, but have declined to say with whom. One of his chief connections to the White House was through Susan Ralston, an assistant who worked for him before she worked for Mr. Rove. Ms. Ralston continues to work for Mr. Rove as a top aide.
A Justice Department spokesman, Bryan Sierra, said he had no comment on the Democratic request for a special prosecutor because the department had not received their letter making the request.
Mr. Sierra said in an interview that there was nothing unusual about the timing of Mr. Hillman's nomination and that it would not affect the Abramoff inquiry. "The team that Noel put together is going to remain together," he said. "The investigation should not be impacted." He said Mr. Hillman would be temporarily succeeded as head of the public integrity office by Andrew Lourie, a career prosecutor in Florida.
The White House had been poised to nominate Mr. Hillman for the bench last year. Mr. Sierra said he did not know why the nomination had been delayed until this week, but he said he believed it had nothing to do with the Abramoff investigation.
In a letter sent to the attorney general on Thursday asking for an independent counsel, Senator Schumer and Senator Ken Salazar, Democrat of Colorado, praised Mr. Hillman's office for the investigation that led to the guilty plea by Mr. Abramoff and his former lobbying partner, Michael Scanlon, a former press secretary to Representative Tom DeLay.
"We applaud its pursuit of Mr. Abramoff and his colleagues," they said. "We have no doubt that if the investigation is left to the career prosecutors in that section, the case would reach its appropriate conclusion. Unfortunately, the highly political context of the allegations and charges may lead some to surmise that political influence may compromise the investigation."
