The swift move would promote to the Supreme Court's top job a newcomer who currently is being considered as one of eight associate justices.
"I am honored and humbled by the confidence the president has shown in me," Roberts said, standing alongside Bush in the Oval Office. "I am 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."
"He's a man of integrity and fairness and throughout his life he's inspired the respect and loyalty of others," Bush said. "John Roberts built a record of excellence and achievement and reputation for goodwill and decency toward others in his extraordinary career."
The selection of Roberts helps Bush avoid new political problems when he already is under fire for the government's sluggish response to Hurricane Katrina and his approval ratings in the polls are at the lowest point of his presidency.
A brief delay in confirmation hearings for Roberts, which had been set to start Tuesday, was likely in light of his new nomination and Rehnquist's funeral this week.
Democrats said Roberts will now be held to a higher standard, although they had found little in his record to suggest they would thrwart his nomination as associate justice.
"Now that the president has said he will nominate Judge Roberts as chief justice, the stakes are higher and the Senate's advice and consent responsibility is even more important," Democratic leader Harry Reid said Monday in a statement. "The Senate must be vigilant."
The president met with Roberts in the private residence of the White House for about 35 to 40 minutes on Sunday evening, then officially offered him the job at 7:15 a.m. Monday when Roberts arrived at the Oval Office.
"This had been something that had been in the president's thinking for some time - in case the chief justice retired or that there otherwise was a vacancy," White House press secretary Scott McClellan said. "The president when he met with him, knew he was a natural born leader. The president knew Judge Roberts had the qualities to lead the court."
McClellan said the White House is confident that Roberts can be confirmed by the Senate by Oct. 3. Bush still has to pick a successor for Associate Justice Sandra Day O'Connor, although she said at the time of her retirement announcement that she would remain until a replacement were seated.
Getting a new chief justice of Bush's choosing in place quickly also avoids the scenario of having liberal Justice John Paul Stevens making the decisions about whom to assign cases to and making other decisions that could influence court deliberations. As the court's senior justice, Stevens would take over Rehnquist's administrative duties until a new chief is confirmed.
"The passing of Chief Justice William Rehnquist leaves the center chair empty, just four weeks left before the Supreme Court reconvenes," Bush said. "It's 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 Roberts has been closely scrutinized since he was nominated as an associate justice and that Americans "like what they see. He is a gentleman. He is a man of integrity and fairness." He said Roberts has unusual experience, having argued 39 cases as a lawyer before the Supreme Court. Bush also said Roberts was a natural leader.
The move was engineered to have all nine seats on the high court filled when the court opens its fall term.
The White House is not opposed to a delay in Roberts' confirmation hearings as long as senators vote on the confirmation before the court session begins on the first Monday of October.
"We believe they have enough time to move forward to meet that goal because of all the work that's already been done and Justice O'Connor had previously indicated that she was going to stay on the court until her position was filled," McClellan said.
Bush already had nominated Roberts to take O'Connor's place. It requires just a little paper shuffling to change the nomination for Rehnquist's seat.
White House chief of staff Andy Card informed members of Congress, calling Senate Majority Leader Bill Frist, R-Tenn.; Sen. Arlen Specter, R-Pa., who is the chairman of the Senate Judiciary Committee; Senate Minority Leader Harry Reid, D-Nev.; Sen. Patrick Leahy, D-Vt., the ranking Democrat on the committee; and House Majority Leader Dennis Hastert, R-Ill.
The White House counsel's office notified the Supreme Court through Justice John Paul Stevens, the senior-most member of the court.
Sen. Charles Schumer, D-N.Y., a member of the judiciary panel, said the nomination "raises the stakes" in making sure that the American people and the Senate knows Roberts' views.