“And then,” he said, “I realized that people were probably thinking the same thing 20 years ago.”

“He might be up there another 20 years,” added Mr. Hicks, 40, who recently completed a 30-month sentence and calls himself an admirer of Judge Brown. “And I hope he is.”

The Constitution grants federal judges an almost-unparalleled option to keep working “during good behavior,” which, in practice, has meant as long as they want. But since that language was written, average life expectancy has more than doubled, to almost 80, and the number of people who live beyond 100 is rapidly growing. (Of the 10 oldest practicing federal judges on record, all but one served in the last 15 years.)

The judiciary has grown increasingly reliant on semiretired senior judges — who now shoulder about a fifth of the workload of federal courts. But recently, some courts have also started taking steps that critics call long overdue to address the challenges that accompany jurists working to an advanced age.

“Attention to this area is growing in the judiciary,” said Judge Philip M. Pro, a district court judge in Las Vegas. Judge Pro leads the Ninth Circuit Wellness Committee in California, which focuses on age- and health-related issues facing judges. A similar committee is being established in the 10th Circuit, which includes Kansas.

“Most judges take pride in their work,” Judge Pro said. “They certainly want to be remembered at the top of their game. But a lot of time you're not the best arbiter of that — it's hard to see it in yourself if you're having difficulties.”

Lawyers and colleagues who work with him say that is certainly not the case with Judge Brown.

True, the legal community here has grown protective of him over the years. In his younger days, he was so well known for his temper — lateness, casual dress and the unacceptably imprecise word “indicate” would all set him off — that before hearings one prominent defense lawyer used to take a Valium, which he called “the Judge Brown pill.”

Now, lawyers use words like “mellowed,” “sweet” and “inspirational” to describe him, and one longtime prosecutor began to cry while talking about his penchant for gallows humor. “Sorry,” she said. “It's just I can't imagine practicing without him.”

A few years ago, when they noticed that while speaking in court Judge Brown would occasionally pause, sometimes for what seemed like minutes, lawyers, clerks and fellow judges worried that they were witnessing the beginning of a decline that would make him incapable of doing his job. But he began using an oxygen tube in the courtroom, and the pauses disappeared. (During an hourlong interview in his chambers, he paused briefly just once while trying to recall the last name of Earl Warren, the former chief justice of the United States, but he was without his oxygen tank.)

The consensus is that Judge Brown is still sharp and capable, though colleagues acknowledge that his appearance can be startling. “Physically he's changed a lot, but mentally I haven't noticed any diminution of his ability,” said Judge Monti L. Belot, the former law clerk who now has his own courtroom in the same building, “Which has to be pretty unique.”

Nevertheless, Judge Brown has begun making a few concessions to his age. He still hears a full load of criminal cases, but now he takes fewer civil cases, and he no longer handles any that may result in lengthy trials. He spreads his hearings throughout the week to keep his strength up, and he no longer takes the stairs to his fourth-floor chambers.

Though most federal judges could resign outright and continue to receive their full salary once they reach 65, a majority — like Judge Brown — elect to move to senior status, a type of semiretirement that allows them to continue to work at a full or reduced level. The courts have become deeply reliant on such judges to handle the caseload, but they have also struggled with how to ease out judges whose desire to keep working no longer matches their ability.

In rare circumstances, a panel of judges can vote to remove another judge because of disability, which has happened only 10 times — most recently in 1999. Or, the chief judge of the court can stop assigning the cases to the judge. More often, a trusted colleague will be enlisted to suggest retirement or reassignment to ceremonial duties, said Judge Marcia S. Krieger, a district court judge in Denver who has been surveying judges in the 10th Circuit about aging issues.

Judge Brown has taken the step of asking a few trusted colleagues, including his longtime law clerk Mike Lahey, to tell him when they believe he is no longer capable of performing his job. “And,” the judge said, “I hope when that day comes I go out feet first.”

Born on June 22, 1907, in Hutchinson, Kan., Judge Brown, who had become a prominent local Democrat, first sought appointment by President Harry S. Truman to the federal bench while serving as a lieutenant in the Navy during World War II (at 37, he was the oldest man in his unit). He failed, but in 1962, after a stint as a bankruptcy judge, he was appointed to the district court by President John F. Kennedy . He earned a reputation as a pragmatic jurist whose middle-of-the-road rulings reflect a desire to apply rather than make the law.

Judge Brown is one of four Kennedy appointees still on the bench and the oldest federal judge in the country by six years, according to the Federal Judicial History Office . The only judge to serve at a later age was Joseph W. Woodrough, who was on the Eighth Circuit until 1977, when he died at 104.

For his part, Judge Brown is dismissive of talk of his place in the record books and tired of all the fuss over his birthdays. “I'm not interested in how old I am,” he said. “I'm interested in how good a job I can do.”