As President Barack Obama prepares to nominate somebody to succeed Justice John Paul Stevens, his administration appears to be on a collision course with the Supreme Court in legal disputes that will test the limits of executive power. Those disputes -- involving issues like detainee rights and secrecy -- throw into sharp relief the differences in the records of several leading contenders for the nomination, including Solicitor General Elena Kagan and two appeals court judges, Merrick B. Garland and Diane P. Wood. While any plausible Democratic nominee would probably rule the same way Stevens would have in many areas of law, including abortion rights and the new health care law, executive power may be an exception. Stevens was a critical vote in a five-justice faction that rejected expansive assertions of executive authority by former President George W. Bush. If his successor is more sympathetic to the vantage point of the Obama White House, the balance could shift to a new bare majority that is far more willing to uphold broad presidential powers. Some of those whose names have been floated for the court -- like Gov. Jennifer M. Granholm of Michigan -- have executive experience but no record of expressing expansive views of presidential power. Others -- like Judge Sidney R. Thomas of the U.S. Court of Appeals for the Ninth Circuit, in San Francisco -- have rarely dealt with major executive power cases, although they have a history of viewing government arguments with skepticism in other matters, like immigration appeals. Each of the three potential nominees who have received the greatest attention -- Wood, Garland and Kagan -- has criticized or ruled against aspects of the Bush administration's approach. But the context, timing and forcefulness of their objections varied widely. Of the three, Wood, of the appeals court in Chicago, has the clearest record in favor of protecting civil liberties and taking a skeptical stance toward executive power. Garland, of the Court of Appeals for the District of Columbia Circuit, did not show early public signs of skepticism about the Bush administration approach. But Garland has also cast votes against presidential power. Kagan also has a mixed record on executive powers, but one that suggests she might generally be more sympathetic toward the White House than Stevens. She worked as a White House lawyer during the Clinton administration, when it was facing off against a hostile Congress and seeking ways to act unilaterally. That experienced shaped her major scholarly work, a 2001 law review article in which she explained and defended efforts by the Clinton White House to impose greater centralized control over executive agencies. 