President Bush nominated John G. Roberts Jr. yesterday as the 17th chief justice of the United States, promoting his nominee for associate justice to lead the Supreme Court and the rest of the federal judiciary even before Roberts was confirmed for the first assignment.

Moving swiftly as he copes with the devastation of Hurricane Katrina, Bush announced his decision just two days after the death of Chief Justice William H. Rehnquist and 48 days after picking Roberts to succeed retiring Justice Sandra Day O'Connor. In elevating Roberts, Bush chose the candidate most likely to be confirmed in short order by the Senate, which was poised to ratify the appeals court judge for O'Connor's seat.

The move could ensure Bush's influence on the judiciary long after his presidency ends. In the past half-century, only two other presidents have had the opportunity to name a chief justice to a lifetime appointment. A former Rehnquist clerk, Roberts shares a philosophical outlook with the man he would succeed and, at age 50, would be the youngest chief justice since John Marshall was appointed in 1801, potentially giving him decades to shape the court's direction.

Since O'Connor agreed to remain until her successor is confirmed, the move means that the court could open its next term on Oct. 3 with nine justices sitting. But in shifting Roberts to the center chair, Bush now must find someone else to replace O'Connor, in some ways an even more consequential choice because she cast the swing vote on issues such as affirmative action, abortion and the death penalty for many years.

"It is in the interest of the court and the country to have a chief justice on the bench on the first full day of the fall term," Bush said in the Oval Office before flying to the Gulf Coast for a second time to inspect relief efforts. "The Senate is well along in the process of considering Judge Roberts's qualifications. They know his record and his fidelity to the law. I'm confident that the Senate can complete hearings and confirm him as chief justice within a month."

Roberts, who appeared alone at Bush's side, seemed mindful that he would replace his mentor rather than join him on the court. "I am honored and humbled by the confidence that the president has shown in me," he said. "And I'm very much aware that if I am confirmed, I would succeed a man I deeply respect and admire, a man who has been very kind to me for 25 years."

The Senate Judiciary Committee, which had been scheduled to open hearings on Roberts's confirmation to O'Connor's seat today, decided yesterday to postpone the process probably until Monday in deference to Rehnquist, who will be buried at Arlington National Cemetery tomorrow.

The same liberal groups that opposed Roberts for associate justice declared him even more unfit for chief. "His views are very much out of sync with civil rights, women's rights, privacy," said Nan Aron, president of the Alliance for Justice. "Certainly reviewing so many of those memos and briefs and papers he authored makes one wonder whether he understands how the law affects ordinary people."

Several Senate Democrats argued that Roberts should receive greater scrutiny for chief justice. "The stakes are higher and the Senate's advice and consent responsibility is even more important," said Senate Minority Leader Harry M. Reid (D-Nev.), adding that "the Senate must be vigilant in considering this nomination."

But there was no indication that his nomination faces any significant threat. "He will be an excellent chief," said Senate Majority Leader Bill Frist (R-Tenn.). "I still expect Judge Roberts to be confirmed before the Supreme Court starts its new term on October 3."

Bush always had Roberts in mind for the next chief justice, aides said yesterday. Roberts was first secretly interviewed for a Supreme Court slot in April in anticipation that the cancer-stricken Rehnquist would retire or die. When O'Connor surprised the White House by announcing her retirement in July and Rehnquist declared that he was not stepping down, Bush decided to appoint Roberts to O'Connor's seat.

Even then, aides said yesterday that the president intended to elevate Roberts to chief justice whenever the job came open. "This had been something in the back of the president's mind in case such a scenario came into being, if the chief justice had retired," said White House press secretary Scott McClellan. "The president, when he met with [Roberts], knew he was a natural-born leader."

Bush summoned Roberts to the White House on Sunday, and the two met in the residential quarters at 5:30 p.m. for 30 to 45 minutes, McClellan said. White House Chief of Staff Andrew H. Card Jr. sat in at first and then left the two alone. Bush called Roberts back to the White House at 7:15 a.m. yesterday and offered him the job. Bush made the announcement 45 minutes later.

Card discussed the decision with Frist, Reid, Judiciary Chairman Arlen Specter (R-Pa.) and the committee's ranking Democrat, Patrick J. Leahy (Vt.), while the White House counsel's office called Justice John Paul Stevens, the court's senior member and acting chief, to inform him of the decision. Bush did not call O'Connor to tell her that her retirement may be postponed until after he was on Air Force One flying to Louisiana.

Although the chief justice has no more votes than his eight brethren, he presides over their conferences, sets the initial agenda for considering cases and, when in the majority, assigns which justice will write a ruling, defining the extent of its reach. He also wields a variety of administrative and policy powers not only over the high court but the broader federal judiciary and has a number of unique responsibilities, such as presiding over presidential impeachment trials and appointing the court that reviews secret wiretaps by U.S. intelligence agencies.

Most chief justices have been appointed from outside the Supreme Court, but in the past century they typically had long tenures on lower courts or had served as governors, Cabinet secretaries or, in one case, president. With just two years on the U.S. Court of Appeals for the D.C. Circuit, Roberts boasts no such credential and would be much younger than the colleagues he would lead. Three and a half decades his senior, Stevens, 85, was already a justice when Roberts was an undergraduate at Harvard University.

But Roberts has the advantage of being well known to the justices, having argued 39 cases before the Supreme Court. "He can pull it off because they really respect him," said Leonard A. Leo, executive vice president of the Federalist Society, a conservative legal group. "What other justices look for in a chief justice is honesty, straight-shooting and smarts. That's what they want, and that's what they'll get."

Roberts grew up in Indiana, graduated magna cum laude from Harvard Law School, clerked for Rehnquist, worked as a lawyer in Ronald Reagan's Justice Department and White House, and served as principal deputy solicitor general under Kenneth W. Starr in the George H.W. Bush administration. A decade of private practice earned him the status of one of Washington's most accomplished appellate lawyers before the president put him on the appeals court in 2003.

Documents released from his government service in the past few weeks revealed Roberts to be a strong conservative with a sharp pen opposed to many affirmative action programs, open to more religion in public arenas and deeply skeptical of what he called the "so-called right to privacy" that undergirds abortion and other rights established by the Supreme Court.

As the Senate digests that record in coming weeks, Bush will turn his attention to his second nomination, although advisers believe he is likely to wait to make an announcement until after the final Roberts confirmation vote to avoid complicating that process and to allow him to publicly focus on disaster relief in the Gulf Coast.

Conservative allies will press the White House to pick another Roberts. "He's a perfect fulfillment of the president's promise," said Wendy E. Long, chief counsel to the Judicial Confirmation Network, a group dedicated to promoting judges who will strictly interpret the Constitution. "There's great happiness with him. If there were another Judge Roberts out there, or the closest thing, I think that would be perfect."

In this view, appeals judges such as J. Michael Luttig, Edith Hollan Jones, Priscilla R. Owen and Emilio M. Garza would be leading contenders. Appellate judge Edith Brown Clement, who fled her home in New Orleans because of Katrina, was a finalist when Roberts was chosen and, although not considered for chief justice, she could again be on the list for associate justice. So, too, could Judge J. Harvie Wilkinson III, who was interviewed by Bush in July, although at 60 he may be older than the president would like to ensure a long tenure.

The most prominent candidate on Bush's list is Attorney General Alberto R. Gonzales, his Texas friend who would be the first nation's Hispanic justice, but conservatives vocally oppose him out of fear that he is a closet moderate.

Sen. John Cornyn (R-Tex.), a Bush ally, said yesterday that the president will probably name a woman or a minority to replace the nation's first female justice and offered a vigorous defense of Gonzales. "He would be a very good nominee and one that I would be happy to support," Cornyn said. "I've read about these concerns from some conservatives, and I really wonder where they are getting some of these strange ideas."

Staff writer Jo Becker contributed to this report.

John G. Roberts Jr. accepts President Bush's nomination to be chief justice

of the United States. Senate hearings are expected to begin next Monday.In nominating John G. Roberts Jr., left, to succeed Chief Justice William H. Rehnquist, President Bush said he was "confident that the Senate can complete hearings and confirm him as chief justice within a month."