Three Arab guerrillas attempting to cross into Israel from Lebanon were killed Wednesday in a clash with Israeli troops, an army spokesman said. No Israeli soldiers were injured in the incident, the spokesman said. The clash took place near the border fences on the slopes of Har Dov about 10 miles northeast of the city of Qiryat Shemona, the spokesman said. When an Israeli patrol spotted the gunmen, the guerrillas opened fire, the army said. The patrol pursued the guerrillas and in a brief exchange of gunfire killed the three men, who were carrying one U.S.-made M-16 automatic rifle, four grenade launchers and a large supply of grenades, the spokesman said.