(AP) Chief Justice William H. Rehnquist, ailing from thyroid cancer, defended lifetime appointments for judges as necessary to insulate them from pressures as they deal with politically sensitive issues.

Rehnquist used his year-end report on Saturday to address concerns about so-called activist judges and Congress' move to strip judges of some of their authority.

The 80-year-old wrote the report from home, where he has been recovering since announcing in October that he has cancer.

Few details have been released about Rehnquist's illness, except that it is being treated with chemotherapy and radiation, a combination commonly used for an aggressive type of cancer. Rehnquist missed arguments in about 25 Supreme Court cases during November and December, but has said that he plans to swear in President Bush on Jan. 20.

The chief justice mentioned his condition only briefly at the close of the 18-page report. “On a personal note, I also want to thank all of those who have sent their good wishes for my speedy recovery,” he said.

Rehnquist, who marks his 33rd anniversary on the high court next week, said that there has been “mounting criticism” recently of judges accused of interpreting the law to fit their politics.

Bush and Republican congressional leaders have been particularly outspoken about activist judges, especially those in gay marriage cases. But Democrats also have also accused conservative judges of stretching the law.

Rehnquist said that judges should not be punished by Congress because of their decisions and that their lifetime tenure protects their independence.

“It is not a perfect system - vacancies do not occur on regular schedules, and judges do not always decide cases the way their appointers might have anticipated. But for over 200 years, it has served our democracy well and ensured a commitment to the rule of law,” Rehnquist said.

Speculation has been rampant about when the Supreme Court will have its next vacancy. Generally justices retire in the summer when the court takes a three-month recess, but Rehnquist's health could force him to step aside sooner.

Supreme Court justices are appointed for life by the president and confirmed by the Senate. The average age of the current nine justices is 70.

An Associated Press poll taken in November found that six in 10 Americans support a mandatory retirement age for justices.

Roger Pilon, director of the Center for Constitutional Studies at the libertarian think tank Cato Institute, said justices and federal judges should be subject to term limits, perhaps 15 years.

“Anyone who has dealt with aging parents knows that age can be a problem,” Pilon said. “There are justices on the court who, by their questions on the bench, suggest that they may not be up to the pace.”

Rehnquist said that views on activism are subjective.

“Federal judges were severely criticized 50 years ago for their unpopular, some might say activist, decisions in the desegregation cases, but those actions are now an admired chapter in our national history,” he said.

Rehnquist raised concerns that an already strained relationship between Congress and the federal courts has been exacerbated by criticism and suggestions of impeachment for judges “who issue decisions regarded by some as out of the mainstream.”

In September, the House voted to prevent federal courts, including the Supreme Court, from ruling on whether the words “under God” should be stricken from the Pledge of Allegiance. And last summer, the House voted to prevent federal courts from ordering states to recognize same-sex unions sanctioned in other states.

Rehnquist, in his 19th report on the federal judiciary since being named chief justice, also:

Said that federal courts have cut employees and services to deal with budget problems.

Called on Congress to add judges to overburdened courts, especially appeals courts in Boston, New York and San Francisco.

Said he expects work to continue into 2005 by the panel he set up to answer congressional complaints that judges have been lax in policing themselves.