Chief Justice John G. Roberts Jr. assured the public that members of the Supreme Court are not “exempt” from the ethics rules for federal judges, including the requirement to step aside from a case if there are reasonable doubts about their impartiality.

But each justice gets to decide on his or her fitness to rule on a case, he said Saturday, and their decisions are subject to no further review.

“This is a consequence of the Constitution’s command that there be only ‘one Supreme Court.’ The Justices serve on the nation’s court of last resort,” Roberts said.

Without citing the specifics, the chief justice addressed a controversy that has swirled around the high court in the run-up to the constitutional challenge to President Obama’s healthcare law.

“I have complete confidence in the capability of my colleagues to determine when recusal is warranted,” Roberts wrote in his year-end report on the federal judiciary. “They are jurists of exceptional integrity and experience…. I know that they each give careful consideration to any recusal questions that arise in the course of their judicial duties.”

Some House Democrats and liberal activists have insisted that Justice Clarence Thomas should step aside, or recuse, from the case because his wife, Virginia, led a tea party group calling for the “repeal of Obamacare.”

At the same time, some Republicans and conservative activists have insisted that Justice Elena Kagan should step aside because she was Obama’s solicitor general when the healthcare bill was signed into law in March 2010. A few weeks later, the president nominated her to the high court. Kagan told senators in her confirmation hearing that she would withdraw from any case in which she had done legal work before joining the court.

Kagan stepped aside from more than 20 cases in her first year. In early December, she signaled she would stay out of the Obama administration’s clash with Arizona over immigration enforcement.

But Kagan and Thomas have given no hint they will withdraw from the healthcare case.

The chief justice gently batted aside several suggestions for change. He said the justices as a group have not and should not review a decision by one of their colleagues on whether to drop out of case. Such a policy “would create an undesirable situation in which the court could affect the outcome of a case by selecting who among its members may participate,” he wrote.

He also noted the high cost of one justice stepping aside.

If one of the nine justices were to withdraw from the healthcare case, the outcome could be a 4-4 tie vote. That would leave the law in a muddle because the healthcare’s individual mandate has been deemed unconstitutional in one regional circuit and upheld in another. A justice cannot withdraw from a case “as a matter of convenience or simply to avoid controversy,” Roberts wrote.

The chief justice also warned Congress to keep its distance. Twice, he cast doubt on whether lawmakers can impose an ethics rules on the high court, a separate branch of government. While the justices choose to abide by the current ethics rules, he said, “the limits of Congress’s power to require [them] have never been tested.”

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-- David Savage in Washington

Photo: The Justices of the US Supreme Court sit for their official photograph on October 8, 2010 at the Supreme Court in Washington. Front row (L-R): Associate Justice Clarence Thomas, Associate Justice Antonin Scalia, Chief Justice John G. Roberts Jr., Associate Justice Anthony M. Kennedy and Associate Justice Ruth Bader Ginsburg. Back Row (L-R): Associate Justice Sonia Sotomayor, Associate Justice Stephen Breyer, Associate Justice Samuel Alito Jr. and Associate Justice Elena Kagan. (TIM SLOAN/AFP/Getty Images)