Updated: 6 p.m.

The hospitalization Thursday of Supreme Court Justice Ruth Bader Ginsburg for pancreatic cancer surgery set off quiet speculation about the type of high-court nominee President Barack Obama may appoint.

An opening on the Supreme Court was expected to come at some point during Obama’s four-year term, but not in the early days of his presidency. If a vacancy occurred, Senators would be forced into a high-profile and potentially explosive debate — one that could set the tone for how Obama intends to approach the federal judiciary.

Nominated by then-President Bill Clinton in 1993, Ginsburg, 75, is one of the most reliably liberal members of the Supreme Court.

She underwent surgery Thursday for the cancer, and she is expected to remain in the hospital for several days.

With Ginsburg’s prognosis still unclear, most sources declined to comment on the record regarding potential replacements on the bench.

Obama was not expected to begin nominating candidates to the federal judiciary until sometime in the spring, and even then those nominees were expected to be for district and circuit courts.

Obama and Judiciary ranking member Arlen Specter (R-Pa.) discussed the broader topic of judicial nominations this week during a private meeting at the White House. At that session, Obama told Specter he would tap judicial nominees who could garner Republican and Democratic support.

One source, who asked for anonymity, said that before Ginsburg’s hospitalization, officials in the Obama administration had already started preliminary discussions with outside legal experts and organizations on the possible appointees.

While Republicans and conservative organizations will ratchet up the pressure on Obama to tap a moderate for the Supreme Court, he will also feel significant pressure from his left wing. Progressives will likely push the White House to tap someone who can act as a counterbalance to the court’s phalanx of conservatives, Chief Justice John Roberts and Justices Antonin Scalia, Samuel Alito and Clarence Thomas.

“In order to bring balance back you need a counterweight to Scalia and Alito,” the source said, adding that liberals will also push hard for a woman or minority. “It seems to me this court needs to diversify.”

One name that has made the rounds in Washington is that of Sonia Sotomayor, a 2nd Circuit Court of Appeals judge. Although politically moderate, Sotomayor would likely find support within the liberal community. She was nominated to the Circuit Court by President George H.W. Bush.

Yale Law School Dean Harold Koh has also been mentioned as a potential pick, as have O’Melveny & Myers Supreme Court litigator Pamela Harris, Stanford law professor and former dean Kathleen Sullivan and Merrick Garland, a judge on the U.S. Court of Appeals for the D.C. Circuit.

Pancreatic cancer is an aggressive form of cancer, and its mortality rates are extremely high, according to medical journals. However, because Ginsburg’s tumor was found at an early stage, the likelihood of a full recovery is significantly higher than in most cases that go undetected for extensive periods of time.

Ginsburg had surgery for colon cancer in 1999.

With Ginsburg still hospitalized at Memorial Sloan-Kettering Cancer Center in New York City, politicians and activists largely avoided publicly discussing a potential replacement, instead issuing statements wishing the justice a speedy recovery.

The president has not yet spoken to Ginsburg but wishes her a “speedy recovery,” White House Press Secretary Robert Gibbs said this afternoon.

Senate Judiciary Chairman Patrick Leahy (D-Vt.), whose panel has jurisdiction over Supreme Court nominees, expressed support for Ginsburg.

“Marcelle and I are keeping Justice Ginsburg and her family in our thoughts and prayers at this difficult time,” he said in a statement.

In a statement, National Jewish Democratic Council Executive Director Ira Foreman praised Ginsburg’s record on women’s rights and civil liberties and wished the Supreme Court justice a speedy recovery.

“Our thoughts and prayers go out to Justice Ruth Bader Ginsburg and her family at this time,” the statement read. “As a member of the U.S. Supreme Court, Ginsburg has been a strong supporter of women’s rights and civil liberties throughout her career. Ginsburg, one of our nation’s brightest legal minds, is the first Jewish woman to serve on our country’s highest court.”

Likewise, People for the American Way President Kathryn Kolbert called Ginsburg a “critical and crucial voice for civil rights and civil liberties on the court.”

The conservative Committee for Justice released a statement that, while wishing Ginsburg a full recovery, also highlighted the often grim prospects pancreatic cancer patients face and that her illness “serves to remind the President, the Senate, and groups like CFJ on both sides of the debate that — with two-thirds of the Court being 70 or older as of this September — a Supreme Court vacancy in the near future is a virtual statistical certainty.”