When 17 U.S. service members, held captive and tortured by Saddam Hussein's forces during the 1991 Persian Gulf War, went to federal court demanding nearly a billion dollars in damages from the new Iraqi government, a district judge upheld their claim.

But in June 2004, Judge John G. Roberts Jr. of the U.S. Court of Appeals for the D.C. Circuit said no, in an opinion that affirmed President Bush's authority to strip the courts of power to hear such cases.

Roberts's opinion was unsentimental but also in the mainstream of legal discourse. Two other judges on the same panel, both Democratic appointees, reached the same result, differing with Roberts only in that they would have thrown out the suit on a narrower basis.

Having spent most of his legal career representing others, Roberts began to mark out his own judicial philosophy only two years ago with his appointment to the District of Columbia Circuit. Now, with his nomination to the Supreme Court, his short judicial record is being closely examined for clues as to how he might rule on the nation's highest court.

Both the scope of Congress's authority to regulate intrastate economic activity -- ranging from development to homemade child pornography -- and U.S. anti-terrorism policies remain unsettled areas of the law likely to come before Roberts in some form if he makes it to the court.

In his relatively brief tenure on the bench, he has written that the Constitution may impose limits on Congress's power to protect endangered species within individual states, and he has voted -- just four days before Bush announced his nomination -- to uphold a military trial for a suspected al Qaeda terrorist held at Guantanamo Bay, Cuba.

Roberts is simultaneously skeptical of federal power over the states and supportive of executive-branch power in foreign and military affairs, and his sparse judicial record resembles the conservatism of a man he once worked for at the Supreme Court, Chief Justice William H. Rehnquist.

"I would say that what unites a lot of positions he's taken publicly is that he would be more deferential to the executive branch than a lot of other judges would be," said Richard A. Samp, chief counsel of the conservative Washington Legal Foundation, which represented the ex-POWs. "The fact that he clerked for Rehnquist, who is perhaps of all the justices the most deferential to elected branches of government, may mean that to an extent he follows in the same mold."

Nevertheless, the full extent of Roberts's judicial philosophy remains undeveloped -- at least in his written opinions. How that philosophy may unfurl should he win Senate confirmation to the court remains unknown. For his part, Roberts has said he believes that is not unusual or undesirable.

"[I]n my review over the years and looking at Supreme Court constitutional decisions, I don't necessarily think that it's the best approach to have an all-encompassing philosophy," he told the Senate Judiciary Committee during his 2003 confirmation hearing.

Roberts has participated in more than 300 decisions and orders since joining the D.C. Circuit in May 2003. He has written majority opinions for the court in 40 of those cases, according to the Justice Department.

Because of the D.C. Circuit's jurisdiction over federal regulatory agencies, its docket is heavy on technical cases not likely to cause controversy at Roberts's upcoming confirmation hearings.

But in a handful of cases, Roberts has had to weigh in on high-profile issues.

In Hamdan v. Rumsfeld, Osama bin Laden's alleged chauffeur and bodyguard, Salim Ahmed Hamdan, challenged the validity of a military panel's determination that he was an enemy combatant who could be tried before a military commission.

In November 2004, U.S. District Judge James Robertson agreed with Hamdan, saying he was entitled to prisoner-of-war status under the 1949 Geneva Conventions unless a court decided otherwise.

But on July 15, a three-judge panel that included Roberts ruled for the Bush administration.

Roberts joined an opinion, written by Judge A. Raymond Randolph, ruling that the military commissions are legal under a congressional resolution of Sept. 18, 2001, that authorized President Bush to "use all necessary and appropriate force" against al Qaeda and its backers.

Additionally, the opinion said that the Geneva Conventions cannot be enforced by U.S. courts.

Roberts's skepticism about the Endangered Species Act came in his first written opinion on the court, a dissent from the denial of a rehearing sought by a developer in the case of Rancho Viejo v. Norton.

Citing two Rehnquist court cases limiting Congress's power to regulate intrastate activity or noneconomic activity, Roberts suggested that the three-judge panel that had upheld the endangered species law might have acted inconsistently with Supreme Court precedent.

In a recent case involving homegrown medical marijuana in California, however, the Supreme Court has reaffirmed Congress's power to regulate intrastate activity, suggesting that Roberts might have to revisit his 2003 view.

The ex-POWs' case, Acree v. Republic of Iraq, came to the D.C. Circuit as an appeal by the Bush administration.

The district court had entered a judgment in favor of the POWs, awarding them $957 million out of the new Iraqi government's treasury, in part because the U.S. government had missed a deadline to intervene on behalf of Iraq.

Judges Harry T. Edwards and David S. Tatel dismissed the suit on the grounds that federal law did not permit suits against states that sponsored terrorism, but rather only against individual officials or agents.

Roberts went further. He argued that a 2003 law lifting economic sanctions against Iraq gave Bush the power to bar all terrorism-related claims against Iraq and its officials for conduct under regime.

For all their disagreement, however, Roberts and his two colleagues were careful to note that they could understand each other's point of view.

"We acknowledge that this is a close question," wrote Edwards, joined by Tatel.

"I agree with the majority that this question of statutory interpretation is close, and I do not suggest that the [statute] is unambiguous," Roberts replied.

Roberts ruled that the U.S. could classify detainee Salim Ahmed Hamdan as an enemy combatant.