John Glover Roberts Jr. was sworn in this afternoon as the 17th chief justice of the United States, replacing the late William H. Rehnquist, the mentor for whom he clerked.

The White House ceremony, attended by many of Washington's most influential political leaders, came less than four hours after the Senate voted 78-22 to confirm Roberts.

Speaking briefly after his swearing-in, Roberts said, "I view the vote this morning as confirmation of what is, for me, a bedrock principle, that judging is different from politics. And I appreciate the vote very much."

He thanked President Bush and said, "There is no way to repay the confidence you have shown in me other than to do the best job I possibly can do." He said his aim is to "pass on to my children's generation a charter of self-government as strong and as vibrant as the one that Chief Justice Rehnquist passed on to us."

President Bush congratulated the Senate on its vote today and said the "civility of the confirmation process has served the interest of the nation and reflected very well on the United States Senate." He called Roberts a man "of integrity, deep humility and uncommon talent."

Justice John Paul Stevens, the senior associate justice who has been performing the chief justice's duties since Rehnquist died, administered the oath in the White House East Room, the same room where Rehnquist took his oath of office 19 years ago. In the audience were Vice President Cheney, members of the Cabinet, numerous congressional leaders and other members of the Supreme Court.

Roberts will participate on Monday -- the first Monday in October -- in a Supreme Court investiture ceremony as the justices begin their new term.

The next step will be the nomination of an associate justice, perhaps within the next day or two, to replace the retiring Sandra Day O'Connor. Since that appointee will replace a centrist justice rather than a conservative, many observers expect a sharper battle.

Sen. Arlen Specter (R-Pa.), chairman of the Senate Judiciary Committee, told reporters after the confirmation, "I believe that there's a very decisive bipartisan flavor to this vote. Judge Roberts -- soon to be Chief Justice Roberts -- got half of the Democrats and Senator Jeffords," an independent. "And to come away with 78 votes, considering where the Senate was in such contentious straits earlier this year, I think is really remarkable."

Specter added, "Chief Justice Roberts has great potential for the future to bring a consensus to the court, to have a better recognition of congressional authority and, as he put it, to understand the Constitution responding to the changes in the ages and responding to societal conditions."

Roberts, 50, will be the youngest person in the exalted position of chief justice since John Marshall, an appointee of President John Adams. Marshall took office in 1801 at the age of 45.

Roberts, who also becomes the official head of the federal judiciary itself, is 17th in a line that includes such historic figures as John Jay, Marshall, Roger Brooke Taney, Charles Evans Hughes, Harlan Fiske Stone and Earl Warren.

He represents a new generation at the court as well, being the first member born after Brown v. Board of Education, the 1954 decision that declared unconstitutional separate-but-equal schools. He received his legal training at Harvard Law School after the passing of the activist era of the Warren court and was present at the creation of the administration of Ronald Reagan, in a Justice Department that strived mightily to reverse much of the Warren court's legacy.

Historically, however, an appointee's past has provided little or no guidance to his or her performance on the court, thanks in part to the influence of colleagues, in part to the independence conferred by a life term and in part to a tendency of justices to compromise, lest they dwell in the margins of the law, unable to build majorities or write opinions of consequence.

Justice Hugo Black, for instance, a former Ku Klux Klan member appointed by President Franklin Delano Roosevelt, became a champion of civil rights and voted to desegregate the nation's schools. President Dwight D. Eisenhower commented that the two great mistakes of his presidency were the appointments of Chief Justice Earl Warren and Justice William J. Brennan Jr., who together helped lead the court into what scholars consider its most "activist" era.

President Richard Nixon appointed Harry Blackmun, the author of Roe v. Wade abortion rights case in 1973 who ultimately abandoned Nixon's "hard line" views on criminal law, including the death penalty.

Roberts's choice of Stevens to administer his oath follows the tradition of Warren, who also replaced a chief justice who had passed away, Fred Vinson. Warren asked Justice Black, the senior associate justice, and the court clerk to handle the oaths, one at the White House and one at the court, in 1953.

Roberts's first term will include cases touching on some of the most divisive issues of the times, including assisted suicide, restrictions on abortion, campaign finance and the powers of the U.S. government in virtually every field of regulation on the books.

By modern standards, Roberts's confirmation process went smoothly. A number of Democrats opposed him largely on the basis of memos he produced while an attorney in the Republican administrations of Reagan and George H.W. Bush that caused the lawmakers to question his positions on civil rights and privacy issues, including the right to abortion.

Still, he was approved by a 13-5 vote in the Senate Judiciary Committee, with some Democrats saying he was the best they could get from a conservative president whose ideal justices are Antonin Scalia and Clarence Thomas.