NOW THAT Liza Alexeyeva has reached the United States and been reunited with her husband, the danger is that Western interest in the plight of Russian human rights activists will fade. There is danger, first of all, for Andrei Sakharov himself, whose fast forced the Kremlin into allowing Miss Alexeyeva to emigrate. Without the continued spotlight of Western attention on him, Dr. Sakharov, and his wife, Yelena Bonner, who fasted with him, may be vulnerable to revenge for the embarrassing concession the KGB was forced to make.

Dr. Sakharov's fate bears watching, but there are many others in worse circumstances. They do not have the protection of Dr. Sakharov's internationally known name or the highly privileged position afforded by membership in the Soviet Academy of Sciences. Since the end of the Moscow Olympics in August 1980, Soviet authorities have exiled, arrested and otherwise silenced all branches of the human rights movement in the Soviet Union, including the Helsinki Watch groups, religious groups, nationalists, trade unionists and intellectuals committed to more honest discussion of the regime's strengths and weaknesses.

A few among the many in prison or labor camps are: Yuri Orlov, 57, distinguished physicist and founder of the Moscow Helsinki Watch Group, sentenced to seven years in strict-regime labor camp, followed by five years of internal exile; Anatoli Scharansky, 33, mathematician, another leader of the Helsinki Watch movement, three years in prison, 10 in strict-regime labor camp; Gleb Yakunin, 47, Russian Orthodox priest, founder of the Christian Committee for the Defense of Believers' Rights, five years strict-regime labor camp, five exile; Tatyana Osipova, 32, computer engineer, member Helsinki Watch, five years standard-regime labor camp, five exile; Mykola Rudenko, 61, poet, leader of the Ukranian Helsinki Watch Group, seven years strict-regime labor camp, five exile. There are many more--Jews, Baptists, intellectuals, Lithuanians, workers--with similar sentences, and still others expelled from the country.

In the opinion of some who have seen both, a worse fate than prison or labor camp is to be condemned to a psychiatric "hospital." Especially troublesome or embarrassing activists are subjected to drugs, shock treatments, beatings and much worse. The harrowing story of this system is recounted in the book "Punitive Medicine" by Alexander Podrabinek, founder of the Working Commission to Investigate the Use of Psychiatry for Political Purposes. Mr. Podrabinek is serving three years in a labor camp. The other members of the small commission have also been arrested and given stiff sentences.

The clear lesson of the Sakharov fast is that criticism from the West makes a difference. It is easy for the ordinary American citizen to feel powerless against the Kremlin. Sometimes it even seems as though Western attention makes matters worse. Yet exiled Russians all say the same thing: the individuals on whose behalf there is constant pressure from the West may be helped. Without that pressure, activists in or out of prison are surrounded by what Dr. Sakharov calls "a wall of silence," within which the KGB has free rein.