When Tamara Ana Maria Arce was found in a small town not far from here, she knew nothing of her history as one of Argentina's cases of political disappearance.

Just short of her ninth birthday, she was living with a couple whom she knew as her adoptive parents and two children who treated her as a sister. Her natural mother, she had been told, had left her when she was an infant.

What she did not know was that her mother actually had been abducted, tortured and imprisoned by Argentina's military, or that she had later searched for two years for her daughter in Argentina and Europe. Tamara had never seen the advertisements in the Buenos Aires papers seeking information with her name and baby picture; she had never heard of the human rights organizations that had made her part of an international campaign.

Tamara Arce was one of this turbulent country's missing children, one of dozens who "disappeared" with their parents during a bloody military campaign against leftists during the 1970s. Most of the disappeared, estimated to number between 6,000 and 15,000, are presumed to have been killed by the military. Many of the more than 120 missing children, however, are believed to be alive.

Tamara is slowly discovering that she is one of the special cases: a disappeared child who has been found and returned to the family.

Her guide in her new life is her natural mother, Rose Mery Riveros, who during five years and four months in Argentina's political prisons and two years of exile never knew whether the 17-month-old daughter she left with a friend was still alive.

The friend, Riveros finally learned, also disappeared while attempting to hide with the girl. But Tamara was supported for seven years by a poor Argentine family who, after finding her abandoned by a paramilitary squad, left Buenos Aires to hide in the countryside and raise a stranger's child.

In June, Buenos Aires human rights workers finally located Tamara and last month mother and daughter were reunited in Lima, Peru. It was the first time they had been together since December 1975.

"I went through years without knowing anything of my daughter, without even being able to ask anyone about her," said Riveros in a recent interview in Lima. "Tamara thought I had abandoned her; she hated me."

Now, said Riveros, Tamara "knows I didn't abandon her, and she is beginning to understand."

Even for Argentines, slowly emerging from a decade of political turmoil and harsh military rule, the Riveros' story is not easy to grasp. It is a portrait of a family dislocated and all but destroyed by violent events in which sheer chance entwined friends and strangers in the family's fortunes.

With the end of military rule approaching, thousands of such stories have begun to circulate. They have become the most emotional theme in national politics and, as pressure grows to investigate disappearances and bring military officers to trial, the issue has become the most serious obstacle to a peaceful return to democratic government.

For Argentina's human rights organizations, the distinction of the Riveros case is that it is one of the few that have been successfully resolved. The Grandmothers of the Plaza de Mayo, an organization that investigates instances of missing children, has evidence of 126 disappeared children who have not been found, and leaders say they suspect there are many more. Only 11 have been found so far.

"This is a problem that is going to affect a whole coming generation in Argentina," said Maria Isabel Chorobik de Mariani, the president of the group and one of those who arranged Tamara Riveros' return to her mother. Many missing children, she said, are believed to have been turned over to adoption agencies or orphanages. Others, however, may have been directly placed with families by military officials who falsified birth records and other documents to disguise the origin of the children.

"If we knew of a case where a military officer had a child, we cannot simply go and ring the doorbell and ask for it," said Mariani carefully. "But the moment will arrive when all of this will have to be brought out."

Tamara Arce's case is different from most because she was never herself taken by military forces. Instead, she was swept almost randomly from family to family until her very presence became a source of danger.

Her fate was governed by commonplace coincidences. On the morning of Dec. 23, 1975, Rose Mery Riveros overslept and decided to leave Tamara with her roommate, Lilliana Molteni, rather than stop at the nursery of the textile factory outside Buenos Aires where the two women were co-workers and union activists.

Later that day, Riveros--who was separated from her husband--was arrested while waiting for a commuter train home. That afternoon, Argentine guerrillas had attacked a nearby military barracks. Because she was an immigrant from Bolivia, Riveros said, she was taken to a police station for questioning. There, military officials identified her as a union activist, and like dozens of other such workers, she "disappeared" from the police station into the clandestine prison system of the Army.

Now, speaking quietly in a Lima apartment, Riveros tries to measure her officially unacknowledged, nightmarish experience in two secret prisons with exact dates, places, and times. She spent two months and two days in Army jails, she says, and was beaten, tortured with electric shocks and repeatedly raped for 12 consecutive days. When she was finally turned over to the official Argentine prison system in February 1976, dressed only in a pair of pants and a shirt, she was unable to walk, she says.

"The interrogation was always about who was active in the factory and what politics they had," she said. "I just kept thinking about my daughter. I thought that if I said anything about other people, they would find my friend and take her and my daughter."

In fact, Lilliana Molteni had taken Tamara and gone into hiding, fearful that she would be the next to be arrested. Riveros, of course, did not know that. For five years in a Buenos Aires' women's prison, while she was held on unspecified charges of endangering national security, she says she never admitted the existence of her daughter to authorities.

Nor did she ask for information from her Bolivian mother, who traveled to Buenos Aires once a year for a visit, for fear that she would be overheard and Tamara would be found and taken away.

"A lot of the time I was sad about her," said Riveros of Tamara. "But I went on thinking she was alive and safe with my friend. If I had not made myself believe that, I would have never survived in jail."

It was not until April 1981, when Riveros was released from prison and expelled to a prearranged exile in Switzerland, that she was able to begin the search for Tamara. With little ability to investigate in Argentina, she said, she began to travel through Europe in search of Argentine exiles who might have known her friend Lilliana through her union activism. Riveros denies that either she or her friend was connected to Argentine guerrillas or other radical political movements.

Riveros traveled first to France, but in a week there found no one who knew of Lilliana or Tamara. So she saved money again and in September 1982, went to Spain.

"I was looking for a certain man who might have known Lilliana," she said. "For a week I did nothing but get on and off Spanish trains, trying to find where he was."

Finally, Riveros located the man in a fishing town in northern Spain. "He said, 'The only thing I can tell you is that Lilliana disappeared. I don't know about your daughter,' " Riveros said. "It was a terrible blow."

Molteni, Riveros learned later, had moved with Tamara into a rented room in a Buenos Aires suburb one night in June 1976, after months on the run. The next day, paramilitary forces swept the neighborhood in search of suspects and Molteni was carried away in a blanket by armed men. She was never heard from again.

The paramilitary officers left the infant Tamara behind in the rented room, according to the Argentine Grandmothers' organization. When the family that had rented the room to Molteni asked them what should be done with the child, they were told she would be picked up later.

"The next day the family went to the police with the child," recounted Riveros, who heard the story from the family. "The officer there told them to get out with the child or the same could happen to them as to Lilliana."

Badly frightened but unwilling to abandon a helpless infant, the poor Argentine family immediately left home and moved to the small town of Guernica, 30 miles from Buenos Aires. There they stayed and raised Tamara for seven years, never mentioning her history to anyone. Even now, according to the Grandmothers' group, the family refuses to be publicly identified or interviewed for fear of retribution.

"It was a real case of human generosity," said Mariani of the family. "This was a family without much means. They were left with this child by a woman who had arrived a day before. It was dangerous, and they could have left her in the street. But they raised her like their own daughter."

The Grandmothers organization found Tamara after Riveros mailed them a picture that was published with her name in Buenos Aires newspapers. In June, Mariani said, the Grandmothers received an anonymous phone call from a man who told them where Tamara was.

Weeks of visits and careful preparation followed before both Tamara and her adopted family accepted the idea that she should return to her mother.

"The family loved her," said Mariana. "But Tamara wanted to go to her mother. She seemed to feel it was just the right thing for her."

Riveros and Tamara met last month at the international airport in Lima, where the two planned to stay briefly before moving back to Switzerland and a new life. "It has been a big adjustment for both of us, but we are coming through," Riveros said.

As Riveros spoke, Tamara hugged her mother's knees and peeked shyly around her skirt.

"In the airport, my legs were trembling because I didn't know how Tamara would react," Riveros said. "When she came, she just looked at me. She didn't want to talk. She just looked and didn't smile. Then a cameraman came and she grimaced and smiled for the cameras. It was the first moment, the supreme moment."