The former wife of Dr. Robert S. Rixse, the 37-year-old Alexandria physician who was fatally shot in the head July 1, has complained to Alexandria officials that city police officers investigating Rixse's slaying have used "Gestapo techniques" against her.

Diane B. Robinson of Marietta, Ga., who was divorced by Rixse in 1981, did not specify what actions the investigators had taken, but stated repeatedly in her Nov. 12 letter to the city's public safety director that the detectives would "harass and threaten" her in telephones calls to her home.

"They are treating her as if she did it," Robinson's attorney, Lawrence B. Custer of Marietta, said yesterday. "She has not been charged with anything. How many times can they keep calling. It's unfair."

Once, Robinson said in her letter, she heard several officers laughing loudly in the background, after Detective Anthony Harper called. Robinson said that after she told Harper that she would consult with her attorney before answering his questions, she heard laughter and Harper telling other officers: " 'She sure don't want to talk to me' (or something to that effect)."

City officials made the letter available yesterday and Assistant Public Safety Director John V. Streeter denied any harassment by police. He said yesterday that Robinson has been "extremely uncooperative and defensive since the investigation started."

He said that she has declined to give the police a written statement on any facts that might pertain to the slaying. "She was married to the guy, she must be able to shed some light on the case."

Robinson has also blocked investigators from speaking to her three children, police said. "Why she feels compelled to not allow the children to help us, I just don't know," said Streeter.

All three were asleep in Rixse's home at 315 Kentucky Ave., when he answered a knock at the front door and was shot.

Robinson could not be reached for comment yesterday and her lawyer said he was unable to comment on the police statements about the case.

Disagreements between Robinson and Rixse over the division of their joint property had continued until his death, according to affidavits filed by friends in the Alexandria Circuit Court.

Rixse, who gained custody of their three daughters after the divorce, was to be married on Sept. 15. His fiance, Rebecca Rubinstein of Boston, was to move to Alexandria after the wedding.

Robinson and her second husband, John K. Robinson, lived in Alexandria's Beverly Hills section at the time of the slaying. Since then they have gained custody of the three children and moved to Marietta.

Rixse had filed a complaint in the Alexandria Circuit Court one month before his death, alleging that his former wife had taken stocks and savings belonging to their daughters and asking for an accounting of the assets. A week later, Robinson filed a claim alleging Rixse had failed to repay a loan from her parents.