President Bush nominated U.S. Court of Appeals Judge John G. Roberts Jr. for the Supreme Court last night, passing over several female candidates to replace the retiring Justice Sandra Day O'Connor in favor of a well-regarded litigator with conservative credentials and friends in both parties.

Bush introduced his choice for the nation's 109th justice in a prime-time East Room ceremony broadcast live on national television after a dramatic day of shifting speculation that captivated Washington. The president hailed Roberts as an impressive legal figure who would interpret the Constitution and laws rather than legislate from the bench.

"John Roberts has devoted his entire professional life to the cause of justice and is widely admired for his intellect, his sound judgment and his personal decency," Bush said, with Roberts at his side. The president added, "He is a man of extraordinary accomplishment and ability. He has a good heart. He has the qualities Americans expect in a judge: experience, wisdom, fairness and civility."

Liberal advocacy groups immediately assailed Roberts for his positions on abortion and other issues. Before the announcement, Senate Minority Leader Harry M. Reid (Nev.) ordered his fellow Democratic lawmakers to offer a more measured response to whomever Bush chose to avoid appearing knee-jerk negative, aides said. But Democrats expect to eventually wage a fight.

"The president has chosen someone with suitable legal credentials, but that is not the end of our inquiry," Reid said in a statement. "The Senate must review Judge Roberts's record to determine if he has a demonstrated commitment to the core American values of freedom, equality and fairness."

Roberts, 50, a resident of Chevy Chase, clerked for William H. Rehnquist when the chief justice was still an associate justice and worked in the administrations of Ronald Reagan and George H.W. Bush. He was appointed by the current president to the U.S. Court of Appeals for the D.C. Circuit two years ago and confirmed by the Senate on a unanimous voice vote. But Roberts made his mark in Washington as one of the most successful advocates before the same high court he would now join.

As a successor to O'Connor, a centrist-conservative who cast the swing vote for years, Roberts is expected to move the court further to the right, but legal experts do not consider him among the most ideological of the candidates Bush considered. Often described as steady and even-tempered, Roberts has accumulated a slim record as a judge but has a longer paper trail as a lawyer for the government and in private practice. That paper trail will surely become fodder for debate in the coming weeks.

Critics have already called attention to his writings on abortion. As deputy solicitor general in the George H.W. Bush administration, Roberts signed a brief on abortion financing that argued in a footnote that Roe v. Wade, which established a constitutional right to abortion, should be overturned because it "finds no support in the text, structure or history of the Constitution."

Some allies and analysts cautioned against reading too much into that because Roberts was reflecting Bush administration policy at the time. At his confirmation hearing for the appellate bench in 2003, he offered a careful answer to the abortion question that likewise was open to interpretation. "Roe v. Wade is the settled law of the land," he testified, adding: "There is nothing in my personal views that would prevent me from fully and faithfully applying that precedent."

Bush picked Roberts after interviewing five finalists Thursday, Friday and Saturday alongside White House counsel Harriet Miers, according to aides. Roberts, who has been teaching international trade law in London, secretly flew back to Washington to meet with the president in the executive mansion's residence for an hour on Friday. Bush spent much of the weekend consulting with his chief of staff, Andrew H. Card Jr., and then "essentially" decided Monday night, aides said.

The White House that night called Roberts, who had returned to London for a class, and told him to fly immediately back to Washington without telling him whether he had the nomination. Bush telephoned Roberts at 12:35 p.m. yesterday to offer him the nomination, the aides said. "I just offered the job to a great, smart 50-year-old lawyer," the president told aides afterward. The judge and his family then joined Bush at the White House for dinner.

In selecting Roberts, Bush passed up the opportunity to name his friend and attorney general, Alberto R. Gonzales, as the first Hispanic on the court, after conservatives attacked him for being too moderate. And Bush chose not to take the advice of first lady Laura Bush, who publicly suggested that O'Connor, the nation's first female justice, be succeeded by another woman.

White House officials said Bush considered several women and minorities, but the aides did not explain why he bypassed them. He began the process by taking the files of 11 candidates with him to a European summit two weeks ago, but the list shifted repeatedly since, aides said. Bush interviewed Judge Edith Brown Clement of the U.S. Court of Appeals for the 5th Circuit at the White House on Saturday, and Republican allies were told Monday night and yesterday morning that she probably would get the nod.

Within hours, though, the White House signaled that she was not the choice, leading some GOP strategists to wonder aloud whether they had been used to spread disinformation or whether Bush changed his mind at the last minute. White House officials said last night Roberts was the only candidate Bush offered the job to and blamed reporters for trusting uninformed Republicans.

The nomination comes at a delicate moment for Bush's presidency, which was struggling with sagging poll numbers, a relentless war in Iraq and a stalled domestic program even before disclosures about the role of his top adviser, Karl Rove, in the CIA leak investigation. Some Republican strategists said the nomination could help the White House divert attention from the Rove scandal and reinvigorate Bush's political prospects.

The prospect of filling the first Supreme Court vacancy in 11 years has already mobilized political forces on both sides to raise vast financial resources in preparation for a struggle akin to a presidential campaign. From the moment O'Connor announced her retirement July 1, interest groups have been airing television and Internet advertising, blitzing supporters with e-mail, and pressuring elected officials to stand strong.

Liberal organizations that have been collecting dossiers on Roberts for months quickly moved to portray him as more extreme than his reputation.

"While he may not have been on Jim Dobson's short list of pre-approved nominees, let's be clear: John Roberts is no mainstream judge," said Wade Henderson, executive director of the Leadership Conference on Civil Rights, referring to one of the nation's most prominent conservative leaders.

Reid wanted to avoid such a reaction from Senate Democrats, concerned about falling into what he considered a Republican trap of condemning a nominee before hearings start, aides said. Sen. Charles E. Schumer (D-N.Y.) said in an interview that the Democratic strategy is to withhold judgment for now, but he predicted an inevitable fight with Republicans over opening up Roberts's records and forcing him to talk about abortion and other topics. "The threshold question is: Will he be forthcoming in both answering questions and making available documents about his previous record?" he said. If Roberts refuses, as many Republicans expect, Schumer said Democrats will take the question to the public.

"We know Judge Roberts is no Sandra Day O'Connor, and the White House has sent a clear signal," Sen. John F. Kerry (D-Mass.), who lost the presidential election to Bush in November, said in a statement. "There are serious questions that must be answered involving Judge Roberts's judicial philosophy as demonstrated over his short time on the appellate court."

Conservatives who have pressured Bush to fulfill what they saw as a promise to appoint a justice in the mold of Antonin Scalia or Clarence Thomas pronounced themselves satisfied. "He's going to be a fabulous justice," said Todd F. Gaziano, a scholar at the Heritage Foundation. "He's a very thoughtful person, a very collegial person, a very deliberate person."

Republican senators quickly rallied behind Roberts. "I don't know what his views are [about Roe v. Wade], but groups have raised a lot of money to oppose this nominee," Sen. Jeff Sessions (R-Ala.) said on CNN. "It is incumbent on these senators not to let these groups decide it, and listen to what he says. He has been exceptional in every way."

Roberts, who was born in Buffalo and raised in Long Beach, Ind., and earned undergraduate and law degrees at Harvard University, worked in the Justice Department and the White House during the Reagan administration. After a stint at Hogan & Hartson in Washington, he served as deputy to Solicitor General Kenneth W. Starr under President George H.W. Bush. He was nominated for a seat on the D.C. Circuit in 1992, but his bid disappeared along with the president's reelection hopes. Roberts spent the Clinton administration back at Hogan & Hartson and participated in the recount fight after the 2000 election before being installed on the D.C. Circuit by the current president in 2003.

Suave, telegenic and well-traveled in Washington circles, Roberts is popular in both parties and widely considered among the most talented appellate lawyers of his generation. He argued 39 cases before the Supreme Court and spoke with awe about joining the justices he has appeared before so many times. "I always got a lump in my throat whenever I walked up those marble steps to argue a case before the court, and I don't think it was just from the nerves," he said last night.

Bush has been waiting since the day he took office for an opportunity to reshape a court that, except for the recount case, has bitterly disappointed conservatives over the years.

Although seven of the nine current justices were appointed by Republican presidents, the court has preserved abortion rights, affirmative action and a ban on school prayer -- if sometimes in a more circumscribed form -- while banning the death penalty in some instances and overturning laws against sodomy.

Perhaps no voice on that court has been more pivotal than O'Connor's. With three staunch conservatives on the right and four liberals on the left, O'Connor and sometimes Justice Anthony H. Kennedy have often cast the swing votes, and O'Connor's case-by-case pragmatism has generally forged the tone and direction the court has taken in key opinions. When she announced her retirement, it raised the stakes all the more.

President Bush said his nominee, U.S. Court of Appeals Judge John G. Roberts Jr., "has devoted his entire professional life to the cause of justice and is widely admired for his intellect, his sound judgment and his personal decency." President Bush and U.S. Court of Appeals Judge John G. Roberts Jr. walk past a portrait of President Ronald Reagan on their way to the announcement of Roberts's nomination. The current Supreme Court: Seated from left, Justices Antonin Scalia and John Paul Stevens, Chief Justice William H. Rehnquist, and Justices Sandra Day O'Connor and Anthony M. Kennedy; standing from left, Ruth Bader Ginsburg, David H. Souter, Clarence Thomas and Stephen G. Breyer. Roberts would replace O'Connor, who often cast the swing vote.