The government expelled a prominent Armenian activist Wednesday and stripped him of his Soviet citizenship as punishment for stirring up nationalist sentiment in an ethnic dispute, the Tass news agency said. It did not say where the activist, Paruyr Ayrikyan, 39, was headed or whether he left the Soviet Union. The expulsion came two days after the Soviet leadership rejected Armenia's bid to annex the region and quell the violent struggle between Armenians and Azerbaijanis over control of the small Nagorno-Karabakh region in the Caucasus Mountains. That decision appeared Wednesday on the front pages of national newspapers.