DULUTH, Minn. (AP) _ A retired city police officer took a lethal dose of prescription drugs about the time he shot and killed a Duluth city official, according to officials who have ruled his death a suicide.

Michael Zlonis, the pathologist who performed the autopsy on Nicholas Radulovich, said Wednesday he could not determine whether Radulovich took the drugs before or after he shot Duluth City Personnel Director Ray Rizzi at his home on Jan. 5.

Radulovich, 68, was found dead in his basement about 30 minutes after shooting Rizzi and Rizzi's wife Kathe, who was wounded in the hand.

Police have established no motive for the shootings. Rizzi and Radulovich were neighbors and had been close friends.

Zlonis said Radulovich swallowed lethal doses of painkillers with the trade names Demerol and Darvon or Darvocet. He said Radulovich also took an overdose of the sleep-aid Dalmane, though perhaps not enough to be lethal by itself.

''He had many times the lethal amount of Demerol'' in his system, Zlonis said.

Radulovich, a policeman for 37 years, was forced to retire in 1981 after suffering a back injury in a car accident. The injury caused him constant pain, according to his friends.

Pharmacologists and other medical experts contacted Wednesday said it is difficult to generalize on how overdoses or abuses of such drugs affect behavior.

Cherie Casey, coordinator of a senior citizens chemical dependency program at Mounds Park Hospital in St. Paul, said few doctors fully understand the prolonged effects of medication on elderly people.

''Through the years these people can become addicted to prescription drugs that definitely can affect your thinking,'' she said. ''Mixing such drugs over a period of time can cause feelings of paranoia. Thinking can become distorted.''

EST