An Israeli Army soldier was killed and four wounded in southern Lebanon last night in an ambush by Moslem militiamen, the Army command said today. The slain soldier was the fifth killed in Lebanon since Israeli forces began a massive search operation there for two captured soldiers 10 days ago.

The ambush happened in the village of Jbeil Batzil, three miles north of the Israeli border and inside the Israeli-declared "security zone," the Army command in Tel Aviv said.

It said a 19-year-old corporal was fatally wounded when a "routine reconaissance patrol" encountered Moslem gunmen and a firefight ensued. The soldier died after being flown to a hospital in Haifa, an Army spokesman said.

The Israeli-controlled South Lebanon Army today pounded the vicinity of the attack from its artillery battery in Yata, in the western sector of the security zone, according to security sources in southern Lebanon.

Earlier this week, the Army said it had withdrawn most of the forces it deployed north of the security zone in an unsuccessful search for two Israeli soldiers who were captured by Moslem militiamen in Lebanon on Feb.17.

The Islamic Resistance Front has said that it executed one of the captured soldiers, but Israeli military sources said there was evidence that he may have died of wounds shortly after the ambush.