"The citizens of Oregon, through their democratic initiative process, have chosen to resolve the moral, legal and ethical debate on physician-assisted suicide for themselves by voting — not once, but twice — in favor of the Oregon act," Jones wrote.
Robert McCallum, an assistant U.S. attorney general, said the Justice Department had not yet decided whether to appeal the ruling, a move that could lead to years of litigation.
"We are disappointed with Judge Jones' ruling, and we respectfully disagree with his conclusions," McCallum said.
Jones was appointed to the federal bench in 1990 by President Bush's father.
The Oregon Death With Dignity Act was approved by voters in 1994 and overwhelmingly affirmed three years later when it was returned to the ballot following a failed legal challenge.
The state law allows terminally ill patients with less than six months to live to request a lethal dose of drugs after two doctors confirm the diagnosis and judge the patient mentally competent to make the request.
Jones said Wednesday that the state had followed the wishes of the Supreme Court by striking a proper balance between the interests of the terminally ill and the government's responsibility to protect them.
Gov. John Kitzhaber, a physician, signed the assisted suicide law in 1998. Since then, at least 91 people have used the law to end their lives, most of them suffering from cancer.
But Ashcroft issued a directive on Nov. 6 that would have banned any lethal prescriptions, deciding they did not meet a "legitimate medical purpose" under the federal Controlled Substances Act.
Oregon Attorney General Hardy Myers challenged the directive in court.
Supporters of the Oregon law contended a ruling in favor of Ashcroft would have had a "chilling effect" on nationwide care for the terminally ill because doctors would fear that administering too much pain medication could invite federal prosecution.
Opponents of the law, such as Dr. Gregory Hamilton of Physicians for Compassionate Care, said such arguments are scare tactics. He said Ashcroft made it clear that "aggressive pain management" is considered legitimate medical care even if it may increase the chance of a patient's death.
Steve Bushong, a deputy Oregon attorney general who has defended the state law, argued that regulating doctors has always been the sole responsibility of the states.
Bushong said Congress intended only to prevent illegal drug trafficking by doctors under the Controlled Substances Act, and it left any decisions about medical practice up to the states.
Attorneys representing an Oregon doctor, a pharmacist and several terminally ill patients joined the state against Ashcroft, arguing that even if he did believe he had authority to ban the Oregon law, he did not follow proper procedure to issue the directive.
Ashcroft's order reversed a 1998 opinion by former Attorney General Janet Reno. Jones criticized Ashcroft in court early in the case, calling the directive an "edict" that Ashcroft issued without hearings.
The Netherlands became the first country to legalize mercy killings with a law that went into effect April 1. The law allows Dutch doctors to legally help end the lives of hopelessly ill patients suffering unbearable pain.
