The Bush administration asked the Supreme Court yesterday to block the nation's only law that allows physicians to help terminally ill patients die more quickly.

The appeal from Attorney General John D. Ashcroft had been expected since May, when a lower court ruled that the federal government could not punish Oregon doctors who prescribed lethal doses of federally controlled drugs.

Oregon voters approved the law, and since 1998 more than 170 people have used it to end their lives. Most had cancer.

The Bush administration has argued that assisted suicide is not a "legitimate medical purpose" and that doctors take an oath to heal patients, not help them die.

While not as prominent as abortion, the issue is an important one for conservative Christians, who helped Bush win a second term last week. The Justice Department waited until yesterday, the last day possible, to file paperwork at the high court, which has been hearing cases without Chief Justice William H. Rehnquist, who is being treated for thyroid cancer.

Oregon's law, known as the Death With Dignity Act, lets patients with less than six months to live request a lethal dose of drugs after two doctors confirm the diagnosis and determine the person's mental competence to make the request.

Paul D. Clement, acting U.S. solicitor general, said in the appeal that the law cannot stand because it conflicts with the federal government's powers. The Supreme Court probably will decide early next year whether to hear the case.

The high court has dealt with right-to-die cases before. Justices held in 1997 that while Americans have no constitutional right to assisted suicide, states may decide the issue for themselves without federal interference.

Oregon is the only state that has a right-to-die law. At issue for the Supreme Court now would be the bounds of a federal law declaring what drugs doctors may prescribe.

A federal judge and the U.S. Court of Appeals for the 9th Circuit in San Francisco have ruled that federal officials do not have the power to circumvent the Oregon law to punish health professionals in the state.