Gunmen backing opposite sides in the Iranian-Iraqi war used mortars and rocket-propelled grenades in a shootout for control of ancient Baalbeck Wednesday that left at least 19 persons dead beside the world-famous Roman ruins. The city 50 miles east of Beirut was calm but tense yesterday.

Police said "many others are still caught under the debris of buildings and cars" in the fighting between pro-Iraqi and Iranian-backed gunmen.

Many of the wounded were school children who were in class when a rocket hit their building. House-to-house fighting raged across the city of 100,000 inhabitants.

Fighting was between the Lebanese branch of the Iraqi Baath Party and the pro-Iranian Shiite Amal organization, with both sides ignorning initial appeals for a cease-fire. Syrian peackkeeping troops refused to enter until both parties guaranteed to halt the clashes, fueled by a combination of religious, political, and tribal hatreds.

In Tel Aviv, an Israeli military spokesman said Gen. William Callaghan, commander of the U.N. Interim Forces in Lebanon, "did not contribute to reducing tension in southern Lebanon and showed disrespect for human life."

Callaghan, who took over two months ago, was quoted as saying in an interview that he planned to bring all of southern Lebanon under the control of the Lebanese Army and was willing to accept increased U.N. casualties if necessary.