NINE MILE FALLS, Wash. (AP) _ A former San Diego policeman who claimed to have been tied up and shot in his home said Thursday he was forced at gunpoint to write an apology for testifying against fellow officers in a murder case.

Former Lt. Doyle F. Wheeler, 36, charged that San Diego police were involved in the alleged assault Tuesday, in which he was grazed in the head.

Stevens County authorities have confirmed a note was found in Wheeler's home but have refused to disclose its contents or other aspects of the investigation. A San Diego assistant police chief has suggested Wheeler staged the attack.

Wheeler, who retired from the force in 1985 on stress-related disability, said the assailants forced him to write a note ''apologizing to Donovan Jacobs and the San Diego Police Department for lying in the Sagon Penn case.''

He said his assailants tied a rope around his neck, burned his chest and back with cigarettes and warned that if he didn't write the note, ''they would wait until my kids got home and then kill them,'' Wheeler said.

Wheeler had testified last year in a racially-charged case on behalf of Sagon Penn, who was acquitted of murder and attempted murder in the 1985 shooting of two San Diego police officers, one of them Jacobs. Jacobs survived.

Penn, who is black, contended that he grabbed an officer's gun and fired in self-defense, and that the white officers provoked a confrontation because of his race. At trial, Wheeler described Jacobs as ''a racist hothead.''

Wheeler said he thought he recognized one of the attackers as a former informant for the San Diego police.

''I do think it's connected to the Sagon Penn case,'' Wheeler said. ''I do think it's connected to the San Diego Police Department. I do think officers are involved in some way.''

Lt. Louis J. Scanlon, spokesman for the San Diego department, said the allegation is involved ''is farfetched and speculative.''

Stevens County authorities found Wheeler tied and bleeding from the left side of his head at his home northwest of Spokane.

Wheeler's wife's car, which neighbors said they heard screeching from the scene, was was found Thursday in a shopping center parking lot in Spokane, said Spokane County Sheriff's Lt. Dick Lovejoy.

Bob Burgreen, San Diego assistant police chief, on Wednesday described Wheeler as ''a fellow who is really disturbed'' and said he found Wheeler's version of the incident - including dialing 911 with his nose and tongue - hard to believe.