If confirmed by the Senate, he would be the 17th man to hold what is arguably the second most powerful position in the American system - one that the 50-year-old judge could occupy for a quarter of a century or more.
Mr Bush made his announcement in a brief Oval Office appearance before leaving for a second visit to the hurricane-ravaged Gulf Coast. Judge Roberts - who had been the President's choice to succeed Sandra Day O'Connor as one of the eight associate justices on the court - said he was humbled and honoured by the opportunity to succeed Chief Justice Rehnquist, for whom he had once clerked. "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. Thank you, Mr President, for that special opportunity," he said.
Mr Bush is understood to have offered the post to Judge Roberts during a 40-minute meeting at his private residence on Sunday evening. It is a shrewd move, sidestepping much of the opposition that would have arisen had he appointed a conservative from either inside or outside the court as its new chief.
It buys time so that the President can concentrate on the implications of the hurricane, yet probably ensures the court will have its full nine-member complement when it returns for the new term on 3 October, or shortly afterwards.
Judge Roberts' confirmation hearings were due to start today, though they are now expected to take place on Thursday or next Monday because of Katrina. But even for this more elevated position, his endorsement does not seem seriously in doubt. Much of the spadework for his hearings has already been completed. Some Democratic senators who might have been critical have been won over by his charm. Others, up for re-election in states carried by Mr Bush in a landslide, are most unlikely to risk their local voters' wrath by joining forces with the liberal pressure groups fighting the nomination.
Ideologically too, Judge Roberts may be less of a conservative than opponents fear. Since his nomination to succeed Ms O'Connor in July, the media has picked over records of his time as a Justice Department lawyer in the Reagan era, and then as deputy solicitor general for the first President Bush. Admittedly, he emerges as a solid conservative on abortion and church-state links. But he is on record as sympathetic to gay rights, another litmus issue in today's divided America. He comes across as a pedant for detail, but possessed of a keen sense of humour.
Finally, and perhaps most importantly, the overall balance of the court will not be affected, as one conservative chief justice is replaced by another of similar ilk. Supreme Court watchers say he may win the support of 75 of the 100 senators - a more than respectable showing on today's partisan and polarised Hill.
After serving as a clerk in the late 1970s to Rehnquist, who was then an associate justice, he worked under two Republican presidents before entering private practice. Though only 50, he is well versed in the ways of the high court. As an advocate, he has represented the government in 39 Supreme Court cases.
After more than a decade in private practice, he was appointed in 2003 to the bench of the federal appeals court of the District of Colombia, considered the second most important appeals court in the US, and a traditional stepping stone to the Supreme Court.
During his senate hearings then, he did not hide his hostility to abortion. But he added, his own views were "not relevant", and would not prevent him applying the precedent of Roe v Wade, the benchmark 1973 Supreme Court ruling that enshrines abortion rights.
Meanwhile, Justice O'Connor has already agreed to remain on the court until her successor is in place. Assuming Judge Roberts' appointment goes through, the high court will thus be at full strength, removing the danger of 4-4 tied votes.
The real battle will come when Mr Bush names his candidate to fill her vacancy, as Ms O'Connor has long been a critical swing vote. If he names an arch-conservative, a fierce political battle is certain, possibly involving a Democratic filibuster, and Republican retaliation that could bring the Senate to a virtual standstill.
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