Ida Nudel, the only Jewish woman to serve a term in Siberia as a "prisoner of conscience," has disappeared. Nudel, 51, has spent the last 11 years of her life trying to leave the Soviet Union to join her sister in Israel. For her efforts, she was sentenced to four years of internal exile, living part of the time in barracks that housed hardened male criminals.

She was released in March but told she would never be allowed to leave the Soviet Union. Her last contact with the West was on July 13, when she spoke with her sister, and signed off in despair. She was being made a homeless person.

Ida Nudel first requested permission to leave in 1971. At the time she was an economist, working in the Institute of Planning and Production and monitoring hygiene standards in food stores. Permission was refused on the grounds she possessed "state secrets." Her room was bugged. She was followed. She was repeatedly detained and beaten. She was also fired from her job and, in order to avoid the charge of being a parasite, worked as a cleaning woman. She spent the next seven years trying to get out and sending chocolates, photographs, reading material, clothing, food and medicine to imprisoned Jews on the rare visits they could have with their families. She came to be known as the "guardian angel," of the "prisoners of conscience" and in the Soviet Jewish community, she became a legend.

Then on June 1, 1978, she hung a banner from the balcony of her Moscow apartment saying, "KGB, give me my visa." She was arrested and three weeks later convicted of malicious hooliganism and banished to Krivosheina, 1,800 miles east of Moscow. Her main companion was a collie that was with her when she returned to Moscow.

Marcia Weinberg, who is married to Rabbi Joseph Weinberg of the Washington Hebrew Congregation and who heads the Committee for Soviet Jewry here, met Ida Nudel shortly before her arrest. Nudel has been "adopted" as a special prisoner by the sisterhood of the Washington Hebrew Congregation.

After her release, says Weinberg, Nudel told her sister by telephone that she had been told she should "rehabilitate herself and become a good Soviet citizen." In April, she was denied permission to live in Moscow. Then she was sent to Riga. "But when she got to Riga she was told she couldn't live in Riga," says Weinberg.

The last contact she had with her sister came on the 13th of July. Weinberg says Nudel told her sister she had spent one night in a bus station. "This is when we, as a world group, became concerned," says Weinberg. "She's not an alarmist. She said,'Don't try to reach me; I just don't know where I'm going to be. I will try to find you.' It was in that kind of despair she signed off and nobody knows where she is. We know she's not in Moscow and not in Riga." One theory is that she has been sent to a closed city where no Western press or tourists are allowed to go.

On Tuesday, July 20, a delegation from organizations concerned with Soviet Jews met with presidential assistant Elizabeth Dole. Dole, who is a member of Congressional Wives on Soviet Jewry, says Nudel's plight has now been drawn to the attention of the highest levels of the American government. The reduced flow of emigrants from the Soviet Union has been raised again and again at meetings with Soviet officials, says Dole, and it is a concern of which President Reagan often speaks.

The meeting with Dole left Weinberg with a profound sense of the difference between the two nations. "We could call the White House and say 'help.' The United States is a place where government can stop long enough to talk about one human being and that person's plight. It's such a juxtaposition to the Soviet Union where individuals are trampled on and stomped on and lost." Later that day, a vigil was held at the Soviet Embassy on Nudel's behalf; among the speakers was a representative of Dole's office.

What has happened to Ida Nudel is so alien to the American experience that it seems unbelievable. As Weinberg puts it, it is senseless. "It is almost like they are trying to destroy a spirit totally. For what? Why? She's done it already. She's been in exile, she's been in prison. It would just seem enough."

Sometimes the story of a single person can tell more about a system of government than all the statistics in the world. The Soviets have created a martyr, yet another human being who is a living indictment of a system that doesn't work. It is only fitting that when those in the free world think of the Soviet Union they should think, also, of Ida Nudel.