As President Obama searches for a replacement for Supreme Court Justice David Souter, those who know him best think he is looking for a rare combination: a pragmatic barrier-breaker who will be a distinguished jurist and whose nomination will cool the partisan warfare that has marked recent confirmation battles.

White House officials say Obama regards the Supreme Court nomination as a seminal decision that will help put a stamp on his presidency. His first months in office have been marked by a willingness to act boldly on domestic and international issues, and he may be expected to bring that same kind of ambition to filling the Souter vacancy — up to a point.

In private conversations and public comments, Obama has made clear that he wants a justice whose intellect, life experience and temperament will shape the court’s future.

“He’s less eager to send a message than to send a great justice,” said White House senior adviser David Axelrod. “The people he’s considering have something in common. They’re rigorous and well qualified. But they all offer different qualities beyond that. He’ll make a decision at the end of the process as to what combination of qualities he favors. He’s not working off a set of specs.”

Another senior White House official, who spoke on the condition of anonymity to more freely discuss internal deliberations, said, “This is not going to be a bomb-thrower.” Obama “may ultimately decide on a pick that is distinguished in being the first something. But I think they will be a pragmatist above all.”

One Democratic official who has discussed the court with Obama said: “My sense, for a variety of reasons, is that he would want the first one to be a home run. I don’t think he will play it safe by picking just a bland nominee on the basis that the person would be easy to confirm.”

Obama has begun to narrow his choices. A knowledgeable source outside the White House said the list of candidates who are being put through a thorough vetting numbers six. Most outside observers think that the president is almost certain to pick a woman, and the four thought to be under the most serious consideration are Judge Sonia Sotomayor of the U.S. Court of Appeals for the 2nd Circuit, Judge Diane Wood of the U.S. Court of Appeals for the 7th Circuit, Solicitor General Elena Kagan and Michigan Gov. Jennifer Granholm (D).

But White House officials cautioned that public speculation may be overlooking several strong candidates. “Not all the names that are being talked about are out there,” Chief of Staff Rahm Emanuel said.

White House officials hope to finish most of the vetting soon, but presidential interviews with prospective candidates are not likely to begin this week, one official said Saturday. Obama is scheduled to discuss the vacancy Wednesday at a meeting with Senate Judiciary Committee Chairman Patrick Leahy, D-Vt.; Sen. Jeff Sessions (Ala.), the new ranking Republican on that panel; Senate Majority Leader Harry Reid, D-Nev.; and Senate Minority Leader Mitch McConnell, R-Ky.

Many officials said they expect a relatively quick decision. “We didn’t start flat-footed,” Emanuel said.

The president has much to consider in choosing a successor to Souter. On the surface, appointing a liberal will reinforce the ideological balance on social issues that marks the current court — four consistent liberals, four consistent conservatives and Justice Anthony Kennedy in the middle.

But whoever he selects is likely to differ greatly from the 69-year-old Souter, whose opinions and jurisprudence were known for being meticulous but not sweeping.

“I think the idea that President Obama is just going to be trading one progressive for another progressive is actually not going to prove to be true,” said Douglas Kmiec, a law professor at Pepperdine University who shocked fellow conservatives by endorsing Obama during the campaign. “Whoever he picks is going to be younger, intellectually vibrant. That in itself is going to shake up the court.”

Laurence Tribe, a Harvard constitutional scholar who is a mentor and adviser to Obama, said the choice can be bold without provoking a battle with Congress or disrupting the president’s complicated legislative agenda.

Obama may not be able to avoid sparking partisan conflict among outside groups, and one adviser said the president will not shy away from a fight, if necessary, to win confirmation for his choice.

But a longtime adviser said he thinks that Obama would like to use this nomination to signal a change from the tone and tenor of recent confirmation battles. “More than anything, I think he wants … a pick that exemplifies that this city is changing, rather than going back to the old battles,” this adviser said.

Though as a senator he opposed both of President George W. Bush’s nominees, Chief Justice John G. Roberts Jr. and Justice Samuel A. Alito Jr., Obama also admonished liberal interest groups that attacked Democratic senators for supporting Roberts’ nomination.

Given all this, it will be hard for Obama to find a candidate who can fulfill the expectations he has set, as well as the hopes of Democrats and liberals who have waited 15 years for the chance to appoint a justice.

In addition, Tribe said, “being persuasive, being a consensus-builder, matters a lot to the president.” With the court split, the ability to persuade Kennedy and perhaps other conservatives is key to forging outcomes that liberals seek. Justice John Paul Stevens, 89, is currently the chief tactician on the liberal side.

Tribe thinks that Kagan showed such skills in her tenure as dean of Harvard Law School, where she quieted the fractious faculty and won the respect of conservatives by hiring across the ideological spectrum.

But others wonder how effective any new justice can be at such a task. “The justices who have been most successful about moving their colleagues — and I think of (Justices William J.) Brennan and Stevens — have gotten there rather late in their careers, through status and experience,” said Doug Kendall, president of the Constitutional Accountability Center, a liberal think tank. “I’m not sure you can go on the court and move more experienced colleagues.”

Some say a politician might have such skills — they point to former Justice Sandra Day O’Connor, who was once a legislator, and her practical approach to putting together a majority. Granholm would bring a politician’s sensibilities to a court currently composed only of former appellate judges, and the governor certainly has lived through the struggles caused by the faltering economy in her state.

Sotomayor presents the most obvious “first” that Obama could fulfill: She would be the first Hispanic justice. And she offers the most compelling life story: Raised by her mother in a Bronx housing project after her father died, Sotomayor rose to the highest academic achievements at Princeton and then Yale Law School. Some say, though, that she has not distinguished herself on the appeals court.

Wood brings an impressive record as an appeals judge and the kind of constitutional scholarship Obama might find attractive. She probably comes closest to the desire of Kendall and other liberals for a justice who “can go head to head with Justice Scalia in taking the text of the Constitution and showing why it points in a progressive direction.” But her appointment would not meet Obama’s goal of expanding the experience of the court.

Charles Ogletree, an Obama friend and confidant and a law professor at Harvard, said the president cannot meet all his goals for the court at once but is likely to have other chances to fill vacancies.

“The president doesn’t need to be bold,” Ogletree said. “He needs to be calm.”