For the past two weeks, Soviet authorities seeking to silence exiled dissident Andrei Sakharov have stationed police at his Moscow apartment to bar foreign reporters from entering and talking with his mother-in-law.

Yesterday that ban was breached for an interview with The Washington Post.

In the besieged flat, Ruf Bonner, 79, declared that "this repression is aimed at liquidating all information about him, breaking friendships and family ties and achieving the deepest isolation."

Bonner, a spare woman with a face deeply lined by age, Stalin-era imprisonment, and her current worries, sipped a cup of coffee as she related how she has not been outside the apartment since uniformed police began their vigil March 4. She relies on Soviet friends whom the police allow inside to bring her food and news, and has the help of a young woman, Liza Alexeyeva, who has lived with the family for two years and is allowed by the police to come and go.

The police, normally two burly men equipped with pistols, billy clubs and walkie-talkies, frequently turn away known Soviet dissidents after checking their internal passports, and they tell all foreign visitors to go away. Their manager is invariably polite, but unyielding. Plainclothes police in unmarked black Volga sedan usually can be seen parked near the building on Chkalova Street in central Moscow.

The Moscow prosecutor's office has warned Bonner to cease all contact with alleged criminal elements and foreigners or face possible charges. Sakharov was banished from Moscow to Gorki Jan. 22 and accused in the press of passing state secrets to Westerners.

Bonner is free to come and go from the flat but she apparently is unable to bring herself to venture past the police. After her husband, a high Communist Party official was executed during the great purges of the 1930s, she spent about 17 years in prison, labor camp and exile. She apparently links the uniformed guards with those years in a way that keeps her indoors. Her psychological isolation seems profound.

Sitting on a daybed in the small kitchen of the two-room apartment granted her in the 1950s during the Khruschev thaw when she was freed and rehabilitated, Bonner said she believes the authorities intend eventually to send her into internal exile once again.

"That is what will happen to both of us," she said, gesturing at Liza Alexeyeva across the table. "They want to take the apartment from me and prevent my daughter from ever coming to Moscow again."

Sakharov's wife, Elena Bonner, is not included in the Supreme Soviet (national parliament) order signed by President Leonid Brezhnev that stripped all state honors from the 1975 Nobel laureate and banned him to Gorki. She has returned to Moscow several times since his exile, and held several press conferences before the police were stationed at the apartment. Elena Bonner is expected to return soon to Moscow.

Her mother is looking forward to the visit, but the thought hardly penetrates the aura of sadness around the older woman. She said long-time friends of hers among surviving Old Bolsheviks are frightened away by the police presence. "These are people who either defended the Soviet Union from Nazi facism (during World War II) or went through repression because of their beliefs," she said. "But they are old now and afraid to come anymore -- and they did so much to preserve this country."

Born into a czarist-era family of exiles, Ruf Bonner joined the Communist Party around the time of the 1917 Revolution and has remained a member ever since, even though her daughter, Elena, turned in her own party cards years ago. As a rehabilitated Old Bolshevik, she is entitled to special medical treatment and other privileges, but since the troubles began with her son-in-law, friends say, she has refused entreaties from the staff of a special hospital for old revolutionaries to come for a checkup.

Liza Alexeyeva said Bonner's "mood is very low right now. She is very troubled."

"I don't even have the right to receive mail anymore," Bonner said. "All communications have been broken with my family. I have received no photographs of my great-grandchildren and no word from my grandchildren. They call this 'humanism'."

The Sakharov-Bonner family situation is complex, with Elena Bonner's two married children by her first marriage now living in the United States. The son, Alexei, wants to marry Liza Alexeyeva, the 24-year old technician who has lived with Ruf Bonner for two years and is deeply attached to the Sakharovs. This situation has not escaped the attention of the authorities.

They have given Ruf Bonner an exit visa good for several more months to visit her family in the United States, but she refuses to leave without Alexeyeva, who so far has been unsuccessful in obtaining exit permission.

In seeking ways to deal with the outspoken physicist and his equally outspoken wife, who have long been active in the Soviet human rights movement, the state has bitterly attacked Elena Bonner, her children, and Alexeyeva. Last week, a government periodical renewed these attacks.

For Ruf Bonner, isolated in her apartment, the connection between government repression and the histories of both families is inescapable. She remembered that just before her son-in-law was packed aboard the plane carrying him under guard to exile, she told Sakharov to look up an old woman who had once helped her nearly 30 years ago -- during Ruf Bonner's own exile in Gorki.