John G. Roberts Jr. comes from a court with special cachet and a unique reputation in the legal world.

His workplace has long been considered the second-most-important federal bench, after the Supreme Court. When a president's policies or Congress's laws are challenged, the argument often ends up in the U.S. Court of Appeals for the D.C. Circuit, where Roberts has worked the past two years. And because the Supreme Court hears so few cases, it is often the circuit that has the last word.

In disputes such as whether Microsoft used its market dominance to set up an illegal monopoly or whether Vice President Cheney can keep secret the meetings of his energy task force, the D.C. Circuit has been called to referee.

It also has a reputation unrivaled by any other federal appeals court as a breeding ground for Supreme Court justices. If confirmed, Roberts would be the fourth current justice elevated from the D.C. Circuit, joining Antonin Scalia, Clarence Thomas and Ruth Bader Ginsburg. Former chief justice Warren E. Burger was an alumnus of the circuit.

Robert H. Bork, another circuit judge considered for the Supreme Court, was famously rebuffed, and Douglas H. Ginsburg, who now serves as the court's chief, withdrew his nomination after a controversy over his past marijuana use.

Over the past decade, the court has been viewed as increasingly conservative and ideologically disdainful of regulation of business and individuals. It recently handed the Bush administration several victories, including a ruling last week that special military trials for enemy combatants imprisoned at Guantanamo Bay, Cuba, are legal.

Conservatives can credit President Ronald Reagan, whose five appointments to the court in the 1980s firmly ended its dominance by liberals and its longtime reputation as one of the most progressive circuits in the nation. With key decisions in the 1950s, the court greatly expanded the rights of criminal defendants and of people with mental illness.

The D.C. Circuit has nine active judges, including Roberts, and three senior judges. Eight judges were nominated by Republican presidents; four, by Democrats. But legal experts say the heightened division on the court is less about politics and more about the majority's strong emphasis on free-market principles and concern about government infringement on individual liberty.

If confirmed, John G. Roberts Jr. would be the fourth justice on the current high court who served on the U.S. Court of Appeals for the D.C. Circuit.