All eyes were on Justice Sandra Day O'Connor after the Supreme Court wrapped up its term this week.

But while O'Connor and her centrist legacy may have been at the center of attention because of her surprise retirement announcement Friday, the center of power during the term was one chair to her left, where Justice Anthony M. Kennedy -- the court's other center-right swing voter -- sits.

In three crucial cases this term, Kennedy, a 1988 appointee of President Ronald Reagan, defected from the five-member right-of-center bloc that Chief Justice William H. Rehnquist nominally leads.

Kennedy joined with the court's liberals to abolish the death penalty for juvenile offenders, to give local governments a green light to take private property for economic development and to endorse a broad theory of federal regulatory power that denied states the right to override a federal law against homegrown medical marijuana.

O'Connor actually found herself in dissent in most of the court's big cases last term, voting to uphold the juvenile death penalty, to strike down Texas's display of the Ten Commandments, to forbid takings of private property for economic development and to uphold California's right to pass a medical marijuana law.

And she expressed that dissent in what was, for her, an unusually uncompromising tone; she seemed uninterested in keeping her options open for future cases, as she often did in the past.

In the marijuana case, for example, she accused the majority of "threaten[ing] to sweep all of productive human activity into federal regulatory reach."

In hindsight, this may have been a clue to her plans to retire. Referring to the property rights case, Richard J. Lazarus, a professor of law at Georgetown University, noted that it was very uncharacteristic of O'Connor. "It didn't read like an O'Connor opinion," he said. "It made me think she was in a different frame of mind."

For Kennedy's part, not only did he desert the conservative camp on crucial issues, he did so in spite of his past votes and writings on the court, which suggested that he might have come out the other way each time.

"What's up with Justice Kennedy?" Boston University law professor Randy Barnett asked at a forum on the recently concluded term sponsored by the American Constitution Society last week. "He's clearly crossed some kind of a Rubicon. That's the big news of this term."

Kennedy's rulings further angered conservative activists who were already upset with him because of his authorship of the court's opinion last year abolishing state laws against same-sex sodomy.

In a generally disappointing term for the right, some conservatives said the only bright spot in the court's Kennedy-supported leftward movement was that it will help them rally their base to urge President Bush to put a committed conservative on the court.

"As grievous as some of the rulings are," said Jan LaRue, chief counsel of Concerned Women for America, a conservative group that focuses on social issues, "they have the good effect of awakening more Americans to how important each vote on the court is."

There could be two vacancies to fill if Rehnquist, 80 and suffering from thyroid cancer, follows his old friend O'Connor into retirement.

Rehnquist seemed frail last Monday and struggled to speak clearly through a special valve in his throat where doctors performed surgery in October to help him breathe. He seemed in good spirits, however, cracking a joke about the lengthy list of dissenting and concurring opinions in one case.

Rehnquist was being a good sport at the end of a term in which his influence seemed to ebb along with his physical health.

Of the 24 cases decided by a vote of 5 to 4, the conservative coalition of Rehnquist, O'Connor, Kennedy, Antonin Scalia and Clarence Thomas held together in only five, according to statistics compiled by the law firm Goldstein & Howe.

In the previous two terms, the conservative majority had held together in almost half of the 5 to 4 cases, the firm said.

Capital punishment, property rights, state sovereignty and more latitude for official expressions of religious sentiment have all been pet causes of the chief justice in his 33 years on the court. He has helped moved the court to the right on each of these issues during the past decade -- but found himself mostly in dissent on them this term.

Kennedy was the difference-maker in the death penalty case, writing the opinion for a five-member majority that found the country had formed a "national consensus" against executing offenders who were younger than 18 at the time of their crimes.

This implicitly repudiated a position Kennedy had taken in 1989, when he joined the court in upholding the practice. As recently as 2003, he had voted to reinstate a juvenile's death sentence that had been put on hold by an appeals court.

This time, he buttressed his argument with references to other countries' opposition to the juvenile death penalty, drawing fire from conservatives who saw him importing foreign law into the interpretation of the Constitution -- as he had previously done in striking down the sodomy laws.

Notably, Kennedy could have reached the same result in the death penalty case without making such references. "To add that separate section is an example of Kennedy's really declaring his independence from the conservative orthodoxy of originalism," Supreme Court litigator Paul Smith said at the American Constitution Society forum.

On property rights, Kennedy supplied a fifth vote to a four-member liberal bloc to uphold local governments' right to buy out private property when deemed necessary to promote broader economic development.

The property rights activists who brought the case had expected Kennedy's support, based in part on his generally pro-property-rights record on the court.

And in the medical marijuana case, Kennedy joined Scalia in breaking with a recent string of cases in which they and the court's other conservatives had struck down federal laws on the grounds that they exceeded Congress's power to regulate interstate commerce.

But whereas Scalia supplied a separate opinion explaining how his positions then and now could be reconciled, Kennedy simply cast his vote without further comment.

Even when Rehnquist had a majority including Kennedy -- as he did in upholding a six-foot stone monument of the Ten Commandments on the Texas Capitol grounds -- it was a shallow victory.

The fifth vote in his coalition came not from someone who agreed with his long-standing view that the commandments are generally permissible on government property, but from Justice Stephen G. Breyer, who accepted the monument on the much narrower basis that it had not aroused much controversy during its four-decade stay in Austin.

Justice Anthony Kennedy parted ways with the Rehnquist bloc on three big cases in the just-ended court term.Justice Sandra Day O'Connor may have telegraphed her intentions with a more forthright tone of late.