MOSCOW, NOV. 24 -- Josef Begun, a leading Jewish activist and former political prisoner, today picked up his visa to emigrate to Israel but he said he will not use it until his son Boris, 23, is allowed to leave the country as a Soviet citizen.

"Without my son, I will not go," said Begun, a former Hebrew teacher who was released from prison last February. Begun and his wife, Inna, were informed in September that their application to emigrate had been approved, and today they picked up visas that expire Dec. 8.

Begun said Boris' visa was also ready but it was withheld when he insisted on keeping his Soviet citizenship. Unlike other nationalities leaving the country, Soviet Jews emigrating to Israel are required to renounce their citizenship.

"Boris requested an external passport like any other citizen leaving the country," Begun said. Stripping emigrants to Israel of their passports constitutes "clear discrimination" with no basis in published law, Begun said.

He said Boris wanted to keep his citizenship so as to be able to come back to visit relatives he and his wife are leaving behind, including Boris' mother, Josef Begun's former wife. Josef and Inna Begun agreed to relinquish citizenship because they have no relatives here, he said.

After receiving oral permission to emigrate last September, Josef and Inna Begun said they would wait to pick up their visas until obstacles to the emigration of Boris and his family had been cleared.

Begun was attacked earlier this fall in the Soviet government newspaper Izvestia, which accused him of stalling his departure on the advice of Israeli intelligence. The newpaper article referred to a private conversation between Begun and an Israeli here for the Moscow book fair in September in which the Israeli allegedly said Begun would be of more use to the cause of Jewish rights inside the Soviet Union than in Israel.