It is the 40th day of her hunger strike and Tamara Tretyakova can barely walk. When she talks, the effort brings tears to her eyes and her voice trails off into silent despair.

Tretyakova, 38, has lost 35 pounds since she began her fast March 18 to protest the refusal of Soviet authorities to allow her to go with her 6-year-old son to join her husband in the United States. Her husband, Simon Levin, emigrated from here in 1978 and is now an American citizen, living in Deerfield, Ill.

For six years, Tretyakova has applied, been refused and waited, watching her son Mark grow up without a father. Now he clambers up on the sofa next to her and whispers something in her ear. She listens wanly and gently shoos him away.

"I don't live here; I don't live there; I am not living," she says, brushing her short brown hair from her red-rimmed eyes. "Six years is enough, they could have been the best years of my life."

In opting for a hunger strike, Tretyakova resorted to the rarest, most dramatic and drastic of all actions available to Soviet citizens who are refused permission to leave for the West. Whether her desperate act will work is questionable. Last November, several Soviet citizens, joined by supporting hunger strikers in the United States, fasted for permission to leave their country. None was granted an exit visa.

Her friends and family worry for her health. She weighs 97 pounds. Her muscles are depleted, aggravating the limp from the polio she had as child.

She cannot bear noises and has trouble swallowing. When she began her fast, she took rose hip water for its vitamin content, but her stomach could not handle it. Now she has to force herself even to drink water.

On Tuesday, she held a press conference with another hunger striker, Yuri Balovlenkov, now on the 33rd day of a fast also protesting six years of refusals from the Soviet authorities for permission to join his wife and daughters in Baltimore.

A third man, Alexander Pereldik, who began a hunger strike with Tretyakova March 18 in his quest for permission to join his wife and son in Peru, was too weak to join the group.

So far the little group's protests have fallen on deaf ears. But they are determined.

"There is no other way out," said Tretyakova.

Balovlenkov, 36, who has gone on two other hunger strikes during his six-year crusade, has vowed this time to take it as far as he can.

"I will go on fighting until I can spend just one day with" his family, he said. "I can't live this way. My family can't live this way."

Every year, hundreds of Soviet citizens marry foreigners and in most cases, with the proper papers and approvals, they are allowed to leave.

But among those who have married Americans, there is a backlog of about 20 people who for one reason or another have been refused permission to go.

Both Tretyakova and Balovlenkov were told at one point, they would not be allowed to leave for security reasons -- she because of her training in aviation technology, he because he once worked in a radio institute.

Since then, as their pursuit of an exit visa has wound through the labyrinth of Soviet bureaucracy, those reasons have receded in time. Twice Balovlenko was promised a visa, but he never received it. Tretyakova's father-in-law was told in Feburary her case would require a "special decision."

Confusion about where responsibility rests in such cases was apparent from the answers Balovlenkov received to appeals sent to 95 Soviet organizations, offices, ministries and newspapers in January, the month he had been promised more than two years ago that he would receive a visa.

Of the 95 appeals, five were sent back, 12 were forwarded to the Interior Ministry, which oversees the Soviet visa office, three to the prosecutor's office, one to the Supreme Soviet and one to the KGB, or security forces. The rest were unanswered.

Interestingly enough, it was Socialist Law, the journal of the prosecutor's office that sent the letter on to the KGB.

Both Tretyakova and Balovlenkov say the hunger strike was a last resort, an attempt to draw attention to their case in spite of advice from friends who fear that the attention will only back the Soviet authorities into a corner.

Last week, Tretyakova said she got a call from the visa office and was told to come in to their office last Friday. On Thursday, a man came to her apartment. She would not let him in, but through the half-opened door, he told her that there was no point in going to the visa office as long as she continued her hunger strike and continued talking to foreign correspondents.

According to Tretyakova, he also said that if she continued to make noise, she would be expelled from Moscow, apparently to a smaller city.

A week before, on her way to a protest in front of the main visa office in Moscow, Tretyakova and her son were picked up in a car and driven around Moscow, while several men tried to talk her out of her hunger strike. She said she told them she would stop when she got a decision.

Since then, Mark, a restless child who watches television and plays with electronic toys sent by his father, has been afraid to go outside. His mother will not allow him to; she worries about what might happen to him.

Last winter, before she began her strike, Tretyakova had decided that if worse came to worst, her husband should take custody of the boy because, she said, "This is no life for him here."

She prepared the papers and her husband went through American courts to establish custody. They were told that for their son to go to the United States, her husband had to come here to get him.

On Tuesday, her father-in-law went to the visa office and was told that her husband had been denied a visa to come to the Soviet Union.

So they spend the day in her two-room apartment, which she used to share with her sister, brother-in-law and two children until her sister moved her family to their mother's home. The curtains are drawn, filtering out the spring sunshine.

Her family helps with the shopping and cooking for her son; she spends most of the day lying down.

When the tears start, she puts her hand to her mouth, as if to hold the emotion.

"I am just an ordinary woman," she said, "and my problem is so small. I just want to be with my husband and for my son to be with his father."