WASHINGTON – With the news that Chief Justice Rehnquist will not return to the bench this week because of treatment for thyroid cancer, speculation has intensified that he may step down after President Bush’s inauguration. On the list of potential Supreme Court nominees to replace him is Judge Michael McConnell, a jurist with bipartisan appeal who sits on the U.S. Court of Appeals for the 10th Circuit.

The Kentucky native received the enthusiastic backing of conservative groups as well as some prominent liberal law professors when he was nominated to the appeals bench by the president in 2001. He also earned the votes of several Democrats on the Senate Judiciary Committee, though they warned they would not necessarily back him for the top court.

“I think he is very much in the running. … He could be a very appealing consensus candidate,” said Sean Rushton, executive director of the Committee for Justice, a group that advocates for the president’s nominees.

The 49-year-old’s path to the bench has passed through some hallowed liberal ground: After graduating from the University of Chicago Law School in 1979, he clerked for J. Skelly Wright of the U.S. Court of Appeals for the District of Columbia and later for the late Justice Brennan of the Supreme Court.

Judge McConnell was a law professor at the University of Utah before he was nominated to the appeals bench in 2002, and he would likely face a tougher confirmation hearing than he did then.

“If given the ability to be on the Supreme Court, where you can overturn past precedent, he could endanger a number of very important rights,” the general counsel to the People for the American Way, Eliot Mincberg, said.

While Mr. Mincberg said he was concerned about the possibility that the judge would be willing to overturn precedents in such areas as abortion rights and separation of church and state issues, he declined to predict whether the group would oppose a hypothetical nomination.

Before becoming a professor, Judge McConnell worked as a lawyer in the Reagan administration and donated to Republican campaigns, including that of Mr. Bush. Liberals have criticized him for authoring a brief to the Supreme Court supporting the right of the Boy Scouts to fire a gay scoutmaster.

The liberal Alliance for Justice, which lobbies against conservative judges, has said that in his writings, Judge McConnell “has articulated an extreme philosophy of originalism and federalism.” The group warned that he would, for example, restrict the ability of Congress to attach conditions to the money it gives to states – a key method of enforcing civil rights laws.

To the administration, Judge McConnell’s opinions have the attraction of being in line with the president’s faith-based initiative, an effort to allow the government to fund religious-based groups to deliver social services.

At the same time, Judge McConnell has taken positions that cross the partisan divide, and he is not viewed as a “rock-ribbed conservative,” Mr. Rushton said. His complicated views could prove challenging as he tries to appeal to the conservative Republican base.

At his confirmation hearing, he told senators he considered Roe v. Wade to be settled law and would not attempt to overrule it – despite his personal opposition to abortion. However, pro-choice groups said he had signed a petition calling for a constitutional amendment to ban the practice under all circumstances.

Judge McConnell also appeared to disown a number of his more controversial writings, including an article that praised a federal court judge who did not sanction two clergymen who illegally blocked access to an abortion clinic.

He argued against the impeachment of President Clinton, and said the Supreme Court in Bush v. Gore should have given Florida more time to conduct a recount in the 2000 election. He also wrote a brief on behalf of three former Democratic attorneys general disputing the first Bush administration’s policy authorizing the deportation of aliens who face persecution in their home countries.

Some civil libertarians have praised Judge McConnell for advocating the rights of religious minorities. He has been called the driving force behind the Religious Freedom Restoration Act, which raised the burden on governments to justify laws that burden religious practice. The bill was passed by both houses with large majorities, but was struck down by the Supreme Court in 1997, in a decision that Judge Mc-Connell has called a mistake.

His views have driven Judge Mc-Connell to criticize one of the president’s preferred judges, Justice Scalia, for a 1990 opinion holding that Oregon’s prohibition on the use of peyote did not violate the free exercise rights of Native Americans who ingested the drug for religious purposes.

Judge McConnell called Justice Scalia’s opinion “contrary to the deep logic of the First Amendment,” and his use of precedent “troubling, bordering on the shocking.”

Others find his approach alarming.

“His views on separation of church and state come right out of the Middle Ages,” said a spokesman for Americans United for the Separation of Church and State, Robert Boston.

If he were nominated by the president, Mr. Mincberg said, liberal groups would urge Democratic senators to press him on two opinions issued during his time on the court: a dissent that would have allowed the firing of employees involved in union activities, and another opinion which they say implied a willingness to overturn precedents.

But his hypothetical nomination promises to be less rancorous than some of the more conservative alternatives.

One professor of constitutional law, Yale Law School’s Akhil Amar, a self-described registered Democrat, said, “I remain a keen admirer of McConnell, who I think would be a great addition to the Supreme Court.”