Washington ? Even to some in the Senate, the president’s pick for the Supreme Court was a mystery Tuesday.

One Democrat, Sen. Tom Harkin of Iowa, wore a befuddled look as he walked through the Capitol, scanning his BlackBerry for e-mailed insights and wondering aloud, “I don’t know who he is. Do you know who he is?”

It was enough for some to suggest that Judge John G. Roberts Jr. was a “stealth nominee” whose real views on controversial issues such as abortion are unknown. But if Roberts is a new name to many in the country, he’s no stranger to the Bush administration or to the interest groups that have been amassing electronic dossiers for months on every possible nominee.

And with his choice, President Bush signaled that he means to shift the Supreme Court to the right, swinging it in a more conservative direction to match the will of the people as measured in their choices for the executive and legislative branches of government.

That’s likely to set off an epic struggle between conservatives aching to influence the last branch of government beyond their control and liberals who’ve found their last bastion of power there.

There’s no doubt that picking a woman to replace Sandra Day O’Connor would’ve been an easier course for Bush. Even first lady Laura Bush had weighed in with a rare public comment that she’d like to see a woman replace O’Connor, the first woman to serve on the court.

A group of demonstrators prays outside the Supreme Court on Tuesday. The group was praying that President Bush would pick a Supreme Court Justice who would make abortion illegal. Nominee John G. Roberts Jr. once helped write a brief that said Roe v. Wade should be overruled.

And selecting someone with even fewer public comments or rulings on controversial subjects such as abortion might have made it easier to finesse a nomination between the harsh edges of the political left and right.

But that’s not Bush, at least not most of the time. True, he’s angered the right by appearing soft on illegal immigration, in an apparent bid for support from Hispanics. But going back on his oft-repeated vow to pick a true conservative for the court would have been more than a political gambit; it would have been seen as a betrayal to his base with little or no payoff from the opposition.

The right rallied instantly to Roberts, all but breathing a sigh of relief that the president hadn’t gone with a less conservative candidate.

For weeks, conservatives had sent strong signals that they didn’t want Bush to pick his old friend, Atty. Gen. Alberto Gonzales. Throughout the day Tuesday, several had voiced concern about a rumor that the president had settled on appeals court Judge Edith Brown Clement, seen as soft on abortion. “Judge Clement gravely concerns us,” said Troy Newman, the president of the anti-abortion group Operation Rescue.

Where Roberts will come down on abortion cases no doubt will be a key question in his confirmation hearings. He once argued as a Reagan Justice Department attorney for overturning Roe v. Wade, the decision that legalized abortion. But in his confirmation hearings for the federal bench he called Roe v. Wade “settled law” and said he’d rule according to its precedent.

A conservative group called Progress for America, which has vowed to spend $18 million to support the nomination, called Roberts “terrific.” Brian McCabe, the group’s president, said he would “defend Judge Roberts from the left’s predictable and premeditated character assassination attempts.”

There was a split response from the left, more restrained in the Senate and more vocal outside.

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Sen. Harry Reid, D-Nev., his party’s leader in the Senate, said he wanted more information about Roberts. “I will not prejudge this nomination,” he said.

Liberal groups were more critical.

“We are saddened that President Bush chose the politics of conflict and division over bipartisan consensus,” said Wade Henderson, the executive director of the Leadership Conference on Civil Rights. “At first blush, John Roberts may not appear to be an ultra-right judicial activist, but his approach to issues of protecting the rights and freedoms of individual Americans are at best unclear and in some instances deeply troubling.”

Ralph Neas, the president of People for the American Way, said the selection was “disappointing.”

“John Roberts’ record raises serious concerns and questions about where he stands on crucial legal and constitutional issues,” Neas said. “It will be critical for senators and the American people to get answers to those questions. Replacing O’Connor with someone who is not committed to upholding Americans’ rights, liberties and legal protections would be a constitutional catastrophe.”