U.S. Court of Appeals Judge David L. Bazelon, who personified liberal activism for more than three decades on a court often called the nation's second most powerful, said yesterday that he will retire from the bench.

Outspoken, activist, creative and controversial, Bazelon has sat on the appeals court here for almost 36 years -- 16 of those as its chief judge.

His career spanned the terms of eight presidents, beginning with Harry Truman. He held sway over the court as it produced rulings that broadened the rights of criminal defendants and the mentally ill and allowed consumers and environmentalists to challenge successfully the powers that be.

"He was and still is a model of what a judge should be . . . someone who is unafraid to look behind a case to the pattern of social relations it represents and say, 'This is unjust and intolerable in a decent society,' " said Yale law professor Robert Burt, a clerk to Bazelon in the mid-1960s.

Several lawyers and educators said his retirement is symbolic of "an end of an era" -- an era that Columbia Law School Dean Benno C. Schmidt said was one of "very high activism on the court in expanding constitutional rights and imposing judicial versions on public policy and administrative law."

Bazelon, who is 75 and has held semiretired senior status since 1979, said in an interview at a judicial conference in Williamsburg yesterday that he hoped to spend some time writing about law and his half-century career.

"It's time to do something else instead of being tied down to these cases. I'm not going to live forever, and you have to give yourself time to do some writing ," he said, adding that he is having some problems with his memory and felt it was best to step down.

Bazelon said his legal opinions were "influenced by concern for people who were getting the short end of the stick.

"I also knew that the way to do it isn't just to say 'this isn't good.' You have to have a basis for something in the law . There's no question that you don't turn over a judgment for somebody just to be helpful. But the important thing is to let the world know that some things oughtn't to be . . . . Sometimes things are so outrageous that any person in his right mind would act."

Bazelon came to the court in 1949 when he was 40 -- then the youngest judge ever named to the federal bench.

In 1954, he wrote what still stands as his most famous opinion, in which he attempted to change the prevailing legal test for insanity in criminal cases.

The old test held that, in general, a criminal defendant could claim insanity as a defense only if it could be proven that he or she could not distinguish between right and wrong.

Bazelon, establishing what came to be known as the "Durham rule," said that a defendant should not be held criminally responsible -- even if he or she knew that an act was wrong -- if the crime was a product of a mental disease or defect. In 1972, the appeals court abandoned that standard.

For years, the Bazelon court -- considered the most progressive in the nation -- enjoyed the backing of Earl Warren's liberal Supreme Court, but after Warren E. Burger became chief justice in 1969, the tide of high court decisions began to turn against Bazelon.

In 1978, his opinion in a case involving a battle between environmentalists and the Nuclear Regulatory Agency was overturned by the Supreme Court in a stinging decision.

Bazelon had ruled that the agency had not adequately considered environmental factors before licensing the Vermont Yankee Nuclear Power Plant, but Justice William Rehnquist, who wrote the opinion, said the appeals decision was an example of "judicial intervention run riot" and excoriated Bazelon for "Monday morning quarterbacking" of administrative agencies.

Yesterday, Bazelon said the alternating swing between liberal and conservative political and legal decisions may not be "altogether a bad thing."

"Maybe the liberals go too far sometimes," he said. "Maybe the others go too far, and there's a way of getting an equilibrium."

Harvard law professor Alan Dershowitz, once a clerk to the judge, said in 1979 when Bazelon moved to senior status that the judge's "enduring contribution" to the law "has been that he has pressed more questions on the system than any other judge. He has singled out the function of the Court of Appeals more than any other judge -- to raise questions, to open areas for discussion."

Chief U.S. Circuit Court Judge Spottswood W. Robinson III, who formally announced Bazelon's retirement at the conference yesterday, said Bazelon will hear no new cases but will participate in writing opinions on cases that he has already heard.

"He has made his mark on the law and on the history of our circuit court which is both indelible and profound," said Robinson.