President Bush nominated John G. Roberts Jr. 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 he was confirmed for the first assignment.

Bush announced his decision on Monday, 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 already 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, 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 the court could open its next term Oct. 3 with nine justices sitting. 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.

Rehnquist, 80, who had suffered from thyroid cancer for nearly a year, had been on the court since 1972 and was elevated to chief justice in 1986. He was buried Wednesday in Arlington National Cemetery.

-- Peter Baker and Charles Lane

Former clerks of the Supreme Court's chief justice, William H. Rehnquist, stand around his flag-draped casket in the Great Hall of the court on Tuesday.