He has been before the Western world's view so long, demanding attention, speaking out, tugging at the conscience, it is difficult to remember that this man is possessed of human, not superhuman, resilience.

Andrei Sakharov sits slumped in a chair in the study-bedroom of his apartment in central Moscow. His face at 56 is a mass of fatigued flesh and wrinkles. His eyes flicker with an unreadable expression, then focus somewhere in the middle distance. The slump of the shoulders, the sliding voice, the deeply pouched eyes - all is exhaustion.

At one point during an hour's interview, during the brief space between two questions, his eyes dropped closed and he slept for an instant. When he speaks, however, the words compel the listener's attention.

"People in the movement are very tired of the pressure. It is difficult for Westerners outside the country to understand the pressure here, the atmosphere," he said "I consider now that if people have the opportunity to leave Russia, they must do so."

This has been a year of bizarre stresses and heavy blows for the dissident movement on the Soviet Union. Nothing speaks of that more clearly than the obvious physical and emotional exhaustion of Sakharov, who for the past decade has been perhaps the single most consistent and prominent voice to be raised in the Soviet Union for liberation of human rights.

The year opened promisingly for the dissidents, with direct gestures of support from America's newly elected president. In late February President Carter wrote Sakharov a letter, which the Nobel Peace Prize winner picked up at the U.S. Embassy with a flourish, using his chauffeured limousine from the Academy of Sciences.

In the months since, however, the Kremlin has cracked down on the dissidents, arresting more than a dozen of them since last spring and pressuring perhaps two dozen others into emigrating. Carter has changed his tactic of public outspokenness - a policy that was applauded here by human rights activitists but which infuriated President Leonid Brezhnev and other Soviet leaders. Now Carter negotiates quietly with Soviets in Washington. The U.S. Embassy here, has a diplomat who specilized in following the dissident's fates, now spreads this responsibility among many. The days of high-profile involvement in dissident matters have ended.

This is not to say that U.S. diplomats here are no longer interested in the dissidents - many are keenly aware and committed to helping them, but the style has changed and there is a new note of caution.

At the same time, the emigrations have reduced the circle of Sakharov's closest friends, men and women who have spent years of their lives speaking their minds and together bearing the pressures. In recent months, as the circle around him has shrunk, Sakharov has seen the attacks penetrate his family, opening a new line of pressure on him. The stresses of these pressures are apparent.

He speaks of Valentin Turchin, a staunch friend and supporter, a scientist who like Sakharov lost his job when he spoke his consience. Turchin, founder of the local branch of Amnesty International, left for America last month, a reluctant decision that tortured both Turchin and his friends.

For 3 1/2 years, Turchin had no work," Sakharov said. "He lived without any serious hope of getting work. An extremely well-rounded scientist, he is put in a position of being unable to pursue his primary occupation. It is a serious situation for his children."

Sakharov said a similar situation existed with Tatyana Khodorovich, a linguist who administered a welfare fund for political prisoners financed by royalities from the works of exiled Nobel Laureate Alexander Sozhenitsyn Khodorovich was exiled early this month.

"She faced severe problems with the future of her children," Sakharov said. "She was directly told, if you don't leave, you have to face the prospect of criminal proceedings."

"There are the tactics, to arrest a few dissidents and frighten others. For the remnant of our generation of dissidents, it is very difficult. For her to have stayed would have been a suicidal act, since no good would come of it.

During the summer, Sakharov's stepdaughter and her family were allowed to emigrate to Israel. Now, with the family circle reduced, Sakharov finds that his younger stepchild, Alyosha, is being harassed by officials. He has been dismissed from the the institute where he was studying, allegedly because of poor marks. Dismissed makes it impossible for him to be accepted at another institute, and may make him eligible for the military draft.

Sakharov's dissent grew out of his work on nuclear weapons which began in the late 1940s when he was still in his twenties. He had an important role as a theoretical physicist in the country's development of the hydrogen bomb and was made a full member of the prestigious Academy of Sciences at age 32.

His convictions about the moral propriety of his work were flagging, however. Four years ago, he talked about how his conscience drove him to dissent: "I gradually began to understand the criminial nature not only of nuclear tests, but of the enterprise as a whole. I began to look on it and on other world problems from a broader, more humane perspective."

Yet, after 10 years of his efforts and the work and reverses of many others as well, little has changed inside the Soviet Union in terms of liberalizing conditions of life for millions of people and Sakharov knows it.

"There was a tremendous change in the first ten years after Stalin's death (in 1953)" he said. "But by itself, taken as a period from then to now, there has been little change. As Russia appears to the eye, so has she preserved herself."

The dissent's attempts to achieve greater compliance with such accords as the humanitarian provisions of the Helsinki agreement have resulted in no discernible change in such areas as reuniting divided families and freer international travel. Reflecting on this Sakharov said, "I'm still alive and still able to do things and do do what I can . . . I proceed . . ."

Sakharov said he is certain that despite the hardships of 1977 and possibly worse ones in the future, dissent will continue in the Soviet Union.

"The activities against dissidents in recent times have always been cruel. We only know what they do , we can't know what they are thinking. They began to see there was support of a wide group of the population and the regime cracked down because they didn't want any worse trouble.

"I believe that the point is that the dissent movement grows out of the conditions of our lives. So when one layer of ice is removed from the surface of the water, a new crust forms, and then another . . . It is a continous process."