The nomination of John Roberts raises important questions about the future of the Supreme Court. But as a progressive environmentalist, I would rather have Roberts and genuine questions than another one of the judges on President Bush's short list and a lot of bad answers.

Roberts is a conservative. He has worked for conservative presidents and, in doing so, advanced conservative legal positions before the Supreme Court. In his short tenure as an appellate judge, he has written some troubling judicial opinions, including one in a very important Endangered Species Act case that suggests he has an unduly restrictive view of congressional power under the all-important commerce clause of the Constitution -- the basis for federal protections for the environment, workers and civil rights.

But there are critical differences between Roberts and the others on Bush's short list for Justice Sandra Day O'Connor's seat. Indeed, I direct an organization that has vigorously opposed a number of Bush's appellate court nominees because of their hostility to environmental safeguards. I was prepared to immediately oppose some of the people on the short list. Roberts is different.

Unlike Judge Michael Luttig of the 4th Circuit, who once opened an opinion by literally rewriting the preamble of the Constitution to create a more limited government than the Constitution actually establishes, Roberts has a fairly limited judicial record that is devoid of rhetorical excess. Whereas Judge Edith Jones of the 5th Circuit has a reputation for being combative, particularly to plaintiffs' lawyers appearing before her court, Roberts has a quiet, thoughtful demeanor that one of his colleagues described as "Midwest calm." In contrast to Judge Janice Rogers Brown of the D.C. Circuit, who made a name for herself by delivering bombastic speeches that thrill the libertarian right, Roberts made his reputation largely on his undisputed skills as a litigator representing clients in cases before appellate courts and the Supreme Court.

I have particular knowledge about one of these cases, having worked on it. In 2002, the property rights movement was at its zenith; developers had won a string of Supreme Court victories that undercut environmental and land-use laws across the country. That year, the court agreed to hear a challenge to a carefully crafted consensus plan to save Lake Tahoe from the damaging effects of overdevelopment. Facing the prospect of a devastating defeat, the Tahoe Regional Planning Agency did a very smart thing: It hired the best conservative Supreme Court advocate it could find. That advocate was Roberts, and he wrote the best legal brief I've ever read in a takings case. His argument in front of the court aimed at and won the court's two swing votes, O'Connor and Justice Anthony Kennedy, resulting in a surprising and broad Supreme Court victory that stopped the takings movement in its tracks.

Does this prove that Roberts is a fan of environmental safeguards? No. Indeed, his few judicial opinions on these kinds of laws suggest he's skeptical about them. But his work on the Tahoe case does demonstrate that he has the ability to see both sides of a divisive issue. This is a critical quality for a Supreme Court justice. Roberts's combination of intellect, skill, and open-mindedness should temper, at least somewhat, anxiety about his nomination.

Facts may emerge during the confirmation process that lead me to oppose John Roberts's confirmation. And the burden remains on Roberts to explain to the Senate what type of justice he will be if confirmed to the Supreme Court. His judicial opinions to date raise concerns about undue deference to the executive branch and suspicion about the reach of Congress's powers. We really know very little about the philosophical approach he will bring to the job of Supreme Court justice.

The administration must produce documents from Roberts's years in public service. Senators must ask appropriate questions and withhold their consent until they receive a full and careful explanation of his judicial views and philosophy. Too much is at stake for anything less.

Roberts is not the Supreme Court justice I would choose. But before Senate hearings begin, I'm open to the possibility that he will not be what I most fear.

The writer is founder and executive director of Community Rights Counsel, a nonprofit, public-interest law firm in Washington.