IT WAS NEAR the end of May 1978 that Marcia Weinberg traveled to Moscow, making a journey she now calls her most "life-changing experience." With her was her husband, Rabbi Joseph Winberg of the Washington Hebrew Congregation, and other members of the congregation, all of them drawn to the Soviet Union of their ancestors. "I always wanted to go back and see how our grandparents and parents had lived," says Marcia Weinberg. "It was a feeling of roots -- to find where we had started, where we had traveled along the way."

And what they had traveled to escape. Marcia Weinberg and her family known about modern Soviet repression of Jews and about the oppression of Jews who tried to emigrate for Israel. The Weinbergs cared enough to write letters urging the Soviet authorities to let the Jewish activists leave and to free "prisoners of conscience."

But the Weinbergs didn't fully understand what was going on with the Soviet Jewish movement until they began meeting activists in their homes. "They were reaching out to us," she says. "They asked that they not be left alone, that people understand that they want to be able to leave the Soviet Union and go to Israel. If someone is calling out to you, you feel you want to answer."

Then came the day that they met Ida Nudel -- a tiny woman who was by then an almost legendary figure in the Soviet Jewish community. Ida Nudel, known as the guardian angel of the "prisoners of conscience," gave hope where there was none. An economist who in 1971 had been refused permission to go to Israel on the grounds that she possessed "state secrets," Nudel spent the next seven years badgering Soviet authorities to provide humane treatment for imprisoned Jews. She sent prisoners chocolates, reading material, pictures, food, and clothing. She made sure their families had something to bring on their rare visits.

"Anything that could give them a little bit of hope and determination to continue," says Weinberg."There are many people who were prisoners who have said that what came in through Ida made a tremendous difference. She gave them a feeling of not being alone."

If the prisoners were grateful, the Soviet authorities were not. Nudel lost her job. Her room was bugged. "She experienced a number of 15-day detentions and beatings," says Meg Donovan of the Helsinki Commission.

The last time Marcia Weinberg saw Ida Nudel was May 30, 1978. She found her to be worried, "almost despairing that we were forgetting the . . . Jews of the Soviet Union. We won't forget, I promised her."

Two days later, Ida Nudel held up a sign outside her flat, demanding that the KGB give her a visa to Israel. She was arrested and convicted of malicious hooliganism, and sentenced on June 21 to four years of Siberian exile. She is the only Jewish woman among some 20 "prisoners of conscience" who are serving terms for trying to emigrate for Israel.

She is living with her collie in a camp generally reserved for male criminals, not for political prisoners. Details about conditions of Siberian exiles are difficult to verify. One former prisoner traveled to Siberia to see her and found her living in the most primitive barracks, living in fear of the male prisoners at night and isolated from people in the near-by village by day. She kept a knife under a pillow, explaining, "Of course, I won't be able to kill them, but at least I can kill myself."

On a tape smuggled out of Siberia in 1979, she says in a haunting voice, "I do not regret one act of mine. Not in June of 1978, or in any day of my life as a 'refusenik.'

"I do live now as a human being, but it's a life alone, without friends or people to speak with. Without anyone to help when I am ill . . . The first days of my life here were so terrible that there aren't enough words even in Russian to express it . . . Not even the imagination can create a situation like that.

"People are afraid to have contact. Even children [who] play with my dog, they are questioned . . . Only the knowledge that maybe my suffering will give ground to people of good will to understand . . . will bring to me some sort of satisfaction."

Ida Nudel has been "adopted" as a special prisoner by many of the synagogues and sisterhoods in the Washington area. She has not been forgotten, least of all by Marcia Weinberg, who wears a plain silver bracelet that says, "Ida Nudel, 6-21-78," and who now heads the Committee for Soviet Jewry in Washington.

Ida Nudel will be 50 years old this Monday, and her life will be honored during a noontime vigil for her freedom across from the Soviet Embassy. Last week, she was remembered in the postcards sent to Soviet Ambassador Anatoliy Dobrynin asking for her release, and she was remembered at the seders on Sunday commemorating the exodus of the Jews from Egypt.

But she was honored before that in a way that transcends any single faith. One night not too long ago the Weinberg family gathered around dinner and talked about heroes in an unheroic age.

That night they spoke of Ida Nudel.