WASHINGTON – The Supreme Court’s decision yesterday to allow doctors in Oregon to use federally controlled substances to bring about the death of terminally ill patients will open the door for Congress to make its own determination on the matter. But leading Republicans are flinching on whether they intend to step into the fray on the issue.

The court’s 6-3 decision, with Chief Justice Roberts among those dissenting, turned on whether the U.S. attorney general has the authority to interpret on his own a 1971 law that was originally aimed at limiting the sale of illegal drugs. A former U.S. attorney general, John Ashcroft, said five years ago that the 1971 Controlled Substances Act extended to doctors who prescribe lethal doses of medicine. The court ruled yesterday that medical decisions are best left to the Department of Health and Human Services.

Writing for the majority, Justice Kennedy said that the Bush administration’s argument in the case, Gonzales v. Oregon, could lead to the attorney general’s making medical decisions that extend well beyond physician-assisted suicide. Justice Kennedy was joined by Justices Breyer, Ginsburg, O’Connor, and Souter. Justice Scalia wrote the dissenting opinion and was joined by Justice Thomas and Chief Justice Roberts. It was Chief Justice Roberts’s first dissent since joining the court in early October.

Opponents of physician-assisted suicide stressed that yesterday’s case does not constitute a major decision on the part of the court in favor of physician assisted suicide. Rather, they said, it concerns a minor question of administrative law. The Supreme Court ruled on assisted suicide in the 1997 case Washington v. Glucksburg, saying unanimously that the Constitution does not contain a right to assisted suicide. The court has left it up to states to decide whether to regulate the practice.

Still, opponents said the court’s decision yesterday paves the way for test cases in a host of other states by ruling that doctors are free to use federally controlled substances to bring about death. Assisted-suicide laws are pending in several states, including Vermont, California, and Arizona. Opponents of physician-assisted suicide also questioned the majority’s interpretation of a clause in the Controlled Substances Act that limits doctors to prescribe drugs only for “legitimate medical purposes.”

“If the term ‘legitimate medical purpose’ has any meaning,” Justice Scalia wrote in the dissent,”it surely excludes the prescription of drugs to produce death.”

Activists on both sides of the issue acknowledged that Congress could resolve the issue of whether the attorney general has the authority to limit the use of controlled substances by simply clarifying the meaning of the Controlled Substances Act. But leading Republicans resisted calls from activists to wade again into a contentious end-of-life decision the way they did last spring during the Terry Schiavo case.

The majority leader of the Senate, Senator Frist, of Tennessee, said through a spokesman that he was displeased by the court’s decision, but he declined to say whether he will move to amend the Controlled Substances Act to block physicians from using drugs to a lethal purpose.

“We are disappointed and will be reviewing the ruling,” Dr. Frist’s top spokesman, Bob Stevenson, wrote to The New York Sun in an e-mail yesterday.

A doctor who sits on the Senate Judiciary Committee, Senator Coburn, a Republican of Oklahoma, also decried the Supreme Court ruling but declined to call on Congress to take up the Controlled Substances Act legislation.

“Nowhere does our Constitution give doctors the right to take the lives of their patients,” Dr. Coburn said. “Deliberately causing death is never a legitimate medical purpose. By creating another class of human being whose lives have no value, the Supreme Court has put all vulnerable people at risk.”

Justice Thomas wrote a separate dissent in the case to highlight what he regards as an inconsistent ruling on the part of a majority that ruled earlier this year against the use of medical marijuana in California under the Controlled Substances Act. Justice Thomas said in that case the majority interpreted the Act as applying to the “manner” in which drugs are used but departed from that interpretation in Gonzales v. Oregon.

A senior fellow at the Discovery Institute and author of the 2001 book “The Culture of Death: The Assault on Medical Ethics in America,” Wesley Smith, said that while he does not view Gonzales v. Oregon as particularly significant, the dissent by Chief Justice Roberts could portend the new chief justice’s decisions in future cases dealing with end-of-life issues. Mr. Smith said he anticipates cases in which parties will look for the court to guarantee a constitutional right to medical research and he expects Judge Roberts would deny such a request.

“I think the fact that Roberts joined Scalia is encouraging for other cases that might come along on which I might have an opinion, like biotech, and cloning, and right-to-die cases. People will say that somewhere lurking in the First Amendment is a right to research, and I would be really stunned if somebody like Chief Justice Roberts, or Scalia, or Thomas would say there is a constitutional right to that,” Mr. Smith said.

Looking ahead, a senior fellow for legal studies at the Family Research Council, Cathy Cleaver Ruse, said Supreme Court nominee Judge Samuel Alito provided a clue as to how he might have ruled in Gonzales v. Oregon in a case he decided in 1995 involving Medicaid funding for abortions. Writing for the majority, Judge Alito ruled that a Pennsylvania law that limited Medicaid funding for abortions violated a federal administrative statute.

Mrs. Ruse said the ruling showed the same deference to administrative law that the minority block showed yesterday.

The national legal director for the American Civil Liberties Union, Steven Shapiro, said he welcomed yesterday’s ruling and predicted Congress would not get involved in the issue.

“I doubt very much whether Congress wants to get in the middle of this,” Mr. Shapiro said. “I think they’re happy to let states act as laboratories to see what the voters decide. For the moment, though, I think it was perfectly clear that Congress never authorized what the attorney general was trying to do in this case.”