An Armenian activist reportedly has been sentenced to death by a Soviet court for the Moscow subway bombing two years ago in which at least four persons may have died.

Soviet human rights activist Andrei Sakharov told Western Correspondents he has been informed by dissidents in Yerevan, the Armenian capital, that Stepan Zadikyan, about 32, has been found guilty of the bombing and his family told the sentence was death.

Sakharov said the man's relatives were informed of the trial and sentence Friday but details of the court proceeding were unknown. It was impossible to gain confirmation from Soviet authorities.

The explosion occurred Jan. 8, 1977, beneath a subway car in a train approaching Pervomayskaya station. The Soviet press, according to its custom of not reporting acts of violence, did not report the incident at the time. Soviet sources later asserted that four people had been killed.

The bombing was thought to have been carried out by Caucasian nationalists as a protest against Soviet power, according to some sources at the time. But these allegations were never confirmed. Salharov once speculated publicly that it might have been the work of Soviet secret police seeking to discredit the dissident-nationalist movement.

According to Armenian dissidents, Zadikyan and two ther Armenians were arrested in November 1977 and accused of conspiracy to plant a bomb at the Kursk railway station here. The arrests were never publicly reported and no previous connection had been made between those arrests and the fatal subway bombing. Alst June, the official Soviet news agency Tass announced several arrests in connection with the subway blast but gave no names.

Sakharov said he was informed that Zadikyan's trial apparently was closed. He said he had no information on the fates of the other two arrested Armenians. He said Zadikyan reportedly had already served a five-year prison term for anti-Soviet agitation, a standard charge used against human rights dissenters and nationalists.

Sakharov, the 1975 Nobel Peace Prize laureate, said he was told that witnesses favorable to Zadikyan, who would have testified he was out of Moscow at the time of the subway bombing, were not called to testify.