LOS ANGELES, AUG. 10 -- A federal judge ruled today that a doctor indicted in the torture-murder of a U.S. Drug Enforcement Administration agent was kidnapped illegally from Mexico and must be returned.

The decision by U.S. District Judge Edward Rafeedie in the case of Humberto Alvarez Machain, a Guadalajara gynecologist, is expected to complicate further the bitter struggle between the Mexican and U.S. governments over the 1985 slaying in Mexico of DEA agent Enrique "Kiki" Camarena.

Rafeedie said the abduction of the doctor, by Mexicans later paid a U.S. reward, violated Mexican sovereignty. He stayed execution of his order for a week to give federal prosecutors time to consider an appeal.

"The court finds that the United States violated the extradition treaty between the United States and Mexico when it unilaterally abducted defendant from his homeland," Rafeedie said in a 39-page opinion. "The court lacks jurisdiction to try this defendant."

The judge emphasized that he was not dismissing the charge that Alvarez Machain participated in the torture-murder, allegedly by administering drugs to revive Camarena for further interrogation by Mexican drug dealers, but was merely ruling that he could not be tried in the United States without being properly extradited.

Alvarez Machain, who has accused his abductors of shooting him seven times in the foot with a stun gun, showed no emotion as he sat in court wearing a blue prison jump suit. He also faces Mexican charges in connection with the killing.

The doctor is one of 22 people indicted in the United States in the case. Seven have been convicted in two trials here, and several more have been convicted in Mexico, but U.S. authorities have fumed at the lack of strong action against some Mexican officials accused of complicity in the murder.

These include Javier Garcia Paniagua, police chief of Mexico City, and two men under U.S. indictment -- Miguel Ibarra Herrera, former head of the Mexican federal judicial police, and Manuel Aldana Ibarra, former head of the Mexican equivalent of the DEA.

Spokesmen for the Justice Department and DEA said they had no immediate comment on plans to appeal Rafeedie's ruling. They said they stood by the statement that Lourdes G. Baird, U.S. attorney in Los Angeles, made Monday after the conviction of four Mexicans involved in the case: "The government of the United States will spare no effort or expense in its continuing investigation of the circumstances surrounding the kidnaping and murder of special agent Camarena."

Prosecutors have made little secret of their strong feelings about Alvarez Machain and took the unusual step of releasing nude photographs of him to support their denial that he was injured by abductors.

Mexican authorities, enraged by the kidnapping, formally requested extradition of Antonio Garate Bustamante, the former Mexican drug agent who organized it, and Hector Berrellez, the DEA agent heading the Camarena investigation.

A DEA spokesman said Berrellez would not be extradited but declined to comment about Garate Bustamante, who has been under federal protection in the United States along with several of the men who brought Alvarez Machain to El Paso April 3.

Berrellez testified in May that DEA officials authorized payment of $50,000 and expenses to the Mexicans, including officers of the federal judicial police, if they brought the physician to the United States. Berrellez said the DEA took the action after negotiations fell through with representatives of the Mexican attorney general, who promised to deliver Alvarez Machain in exchange for money and a Mexican fugitive now in the United States.

U.S. prosecutors told Rafeedie that, even if the physician were kidnapped, he could be tried in U.S. courts. Rafeedie acknowledged that he found no legal precedent that directly applies to such circumstances and said he based his ruling on laws in other extradition cases.

He rejected a contention that the government was not responsible for the kidnapping, noting testimony that the government paid at least $20,000 of the promised reward and was spending $6,000 a week to support some of the abductors and their families. "The record reveals that the DEA and its informants were integrally involved in Dr. Machain's abduction," Rafeedie said.