Washington - The Bush administration cannot stop doctors from helping terminally ill patients end their lives under the nation's only physician-assisted suicide law, the U.S. Supreme Court ruled on Tuesday.

In a stinging defeat for the administration, the high court ruled on a 6-3 vote that then-Attorney General John Ashcroft in 2001 impermissibly interpreted federal law to bar distribution of controlled drugs to assist suicides, regardless of the Oregon law authorizing it.

The justices upheld a U.S. appeals court ruling that Ashcroft's directive was unlawful and unenforceable, and that he had overstepped his authority.

The Oregon law, called the Death with Dignity Act, was twice approved by the state's voters. The only state law in the nation allowing physician-assisted suicide, it has been used by more than 200 people since it took effect in 1997.

Under Oregon law, terminally ill patients must get a certification from two doctors stating they are of sound mind and have less than six months to live. A prescription for lethal drugs is then written by the doctor, and the patients administer the drugs themselves.

Ashcroft's directive declared that assisting suicide was not a legitimate medical purpose under the Controlled Substances Act and that prescribing federally controlled drugs for that purpose was against the federal law.

The directive threatened to revoke prescription-writing licenses for physicians and pharmacists who filled orders for life-ending drugs.

Writing the majority opinion, Justice

Anthony Kennedy said the federal drug law does not allow the attorney general to prohibit doctors from prescribing regulated drugs for use in physician-assisted suicide under state law permitting the procedure.

Court's Conservatives Dissented

The court's most conservative members -- Justices Antonin Scalia and Clarence Thomas and new Chief Justice John Roberts, who was appointed by President George W. Bush -- dissented.

Ashcroft reversed the policy adopted by his predecessor, Attorney General Janet Reno, during the Clinton administration. Conservative lawmakers and groups had opposed Reno's decision.

The closely watched case pitted the federal government's power to interpret and enforce the nation's drug laws versus the traditional authority of a state to regulate doctors and the practice of medicine.

Bush administration attorneys argued that federal drug law trumped the Oregon law on the issue of whether doctors may prescribe lethal doses of medication to terminally ill patients.

But Kennedy, joined by another moderate conservative, retiring Justice Sandra Day O'Connor, and the court's four most liberal members, rejected the government's arguments.

He said the administration maintained that the law delegated to a single officer in the executive branch "the power to effect a radical shift of authority from the states to the federal government to define general standards of medical practice in every locality."

Kennedy concluded in the 28-page opinion that the text of the federal law shows that "Congress did not have this far-reaching intent to alter the federal-state balance."

Oregon had argued that Congress did not authorize Ashcroft to overrule a state's decision about specific medical uses of controlled substances.