It was a day of once-a-decade pageantry followed by business as usual at the Supreme Court yesterday, as John G. Roberts Jr. strode in at 9:15 a.m. for the first investiture ceremony at the court in 11 years.

Seated in a chair that once belonged to Chief Justice John Marshall, Roberts could look directly across the courtroom at President Bush, as Clerk of the Court William K. Suter read a scroll containing Roberts's formal commission as chief justice.

The senior associate justice, John Paul Stevens, 85, administered the oath of office, which Roberts, 50, had already taken in a private ceremony late last week so that he could get straight to work; Roberts swore, again, to "do equal right to the poor and to the rich."

After Stevens, the court's oldest member, and Roberts, its youngest, posed for pictures in front of the court's long, white staircase, Roberts's 4-year-old son, John, broke the tight grip his mother, Jane Sullivan Roberts, had kept on his hand and ran toward his father. Roberts gathered the boy in his arms.

An hour later, Roberts presided over the court's first oral argument, running the session much as the mentor he replaced, William H. Rehnquist, would have -- right down to the laconic "warm welcome" the late chief used to extend new members of the Supreme Court bar.

At issue in the first case was whether workers at meat and poultry factories are entitled to get paid for time they spend walking to pick up required safety equipment, or waiting to get it.

Twice it seemed that Roberts was about to ask a question, but other justices jumped in first.

When Roberts did ask questions, he showed that he was on top of the matter. What if the workers must change safety clothes several times during the day? Shouldn't they get paid for that time? he asked Carter G. Phillips, a lawyer for the employers in the case.

Phillips responded that such mid-work breaks would be compensable. The problem, he argued, was in expanding the definition of the working day.

As he gets up to speed, Roberts has the assistance of five law clerks, one more than the maximum the other justices have employed. Roberts retained the three clerks Rehnquist had hired and brought two clerks from the U.S. Court of Appeals for the District of Columbia Circuit.

On Wednesday, the Roberts court will face one of its first controversial cases of the term, when it hears arguments about the right to die. The Bush administration seeks to derail Oregon's law allowing physician-assisted suicide, through a policy first adopted by then-Attorney General John D. Ashcroft in 2001. It says the federal government may punish any doctors who prescribe controlled substances to terminally ill patients who want to end their own lives under the Oregon law.

But Oregon says that it has a right to determine legitimate medical practice within its borders, an argument reminiscent of those the court rejected last term in upholding a federal crackdown on medical marijuana in California. The case is Gonzales v. Oregon, No. 04-623.

Later in the term the court will also rule on the constitutionality of a New Hampshire law that requires minors to notify parents before they terminate a pregnancy, with no exception for the health of the teenager.

Chief Justice John G. Roberts Jr., 50, helps Justice John Paul Stevens, 85, down the Supreme Court steps.