ANDREI SAKHAROV refuses to be silenced. Despite everything the Kremlin has done to isolate him, intimidate him and break his spirit, he fights back. His weapons--eloquence, courage and a worldwide reputation as a champion of human rights--are proving difficult for the Soviet authorities to parry. But this unequal struggle, which has escalated steadily since Dr. Sakharov was sent into internal exile two years ago, entered a new phase last week that could quickly end it in a senseless tragedy.

Dr. Sakharov, feeling that he has little else left to lose, embarked on a hunger strike nearly two weeks ago. He is protesting the authorities' refusal to allow his stepson's fianc,ee to leave the Soviet Union and join the man she married last year by roxy. Her detention, Dr. Sakharov feels, is "undisguised blackmail against me." She is, he says, "a hostage of the state," detained so that his hope for her eventual release will keep him from being too troublesome. He is probably right. But he is also an aging man, and reportedly not in good health. His fast will not last very long.

The Kremlin's decision to exile Dr. Sakharov to the closed city of Gorky, only 250 miles from Moscow, was a halfway step that never promised to last for very long. Dr. Sakharov's stature, inside and outside the Soviet Union, as a great physicist, Nobel Peace Prize winner and intellectual leader, as well as the country's leading dissident, apparently protected him from the harsher fate--prison, labor camp, incarceration in a mental hospital--that has befallen hundreds of those who followed his lead.

But Dr. Sakharov has refused to accept a comfortable silencing. He savagely criticized the invasion of Afghanistan and smuggles out messages that are heard everywhere. Gradually conditions have been tightened so that now his apartment is guarded constantly. Friends and family--excepting his wife-- may not visit. He has been beaten by KGB thugs and threatened with psychiatric commitment or sanctions against his wife. He may not use a telephone. His apartment is regularly searched and ransacked. Though he no longer works on classified matters (his security clearance was lifted in 1968), he is now even prevented from trying to keep up with physics. Last spring a smuggled message reported that the KGB had removed his scientific notebooks and manuscripts in "a new attempt to deprive me of any opportunity for intellectual activity, even in my solitude, and to rob me of my memory."

Where this confrontation will end no one can predict. Perhaps the Kremlin will finally realize that internal exile has only amplified Dr. Sakharov's voice and will decide at last to send him and his family out of the country. As the world rightly focuses on his gallant struggle, he would be the first to point out that there are hundreds of others in Soviet prisons, without the protection of a famous name and reputation, whose crime, like his, was to try to get the Soviet government to permit its citizens a measure of intellectual and personal freedom.