Col. Eli Geva, the combat brigade commander who resigned his command because he objected to leading his men in an assault on Beirut, has been discharged from the Israeli Army.

Geva, 32, a highly respected 14-year veteran of the Israeli military, reportedly was willing to remain in the Army and to participate in the fighting in Lebanon, but was not willing to lead his armored brigade into Beirut because he feared a high number of civilian casualties.

The decision by Israeli military officials to discharge Geva was not surprising. His request to be relieved of his duty, which he called a matter of "conscience," caused "deep confusion" among other officers and was a subject of much discussion among enlisted men, according to military officials.

The timing of Geva's resignation was also thought likely to fuel a growing sense of unease here over the prospects for a peaceful resolution of the siege of Beirut and to add to the questioning of whether the destruction of the Palestine Liberation Organization forces trapped in the city would be worth the human and political costs Israel would have to pay to achieve it.

Although Geva comes from a family with a long history of distinguished service in the Israeli military, and although his decision was cheered by critics of the Lebanon invasion, his resigning from a combat command in wartime was criticized by government and military officials.

Speaking in the Israeli Knesset (parliament) yesterday, Prime Minister Menachem Begin said he had spoken with Geva at the request of Defense Minister Ariel Sharon and Chief of Staff Rafael Eitan.

"He told me his complaints," Begin recalled. "He said, 'I am a brigade commander, I look through my binoculars,and I see children there.' "

"I asked him," Begin said, "Did you receive an order to kill those children there? 'No,' he said. So what is your complaint? He didn't have an answer. He thinks perhaps he might get such an order."

Begin added, "The Army is the people's army. It contains people of different outlooks. . . . The Army is wonderful, disciplined."

Geva's decision was also criticized by two former Israeli chiefs of staff, Haim Bar-Lev, the secretary of the opposition Labor Party, and Yigael Yadin.

Bar-Lev said that no officer has the privilege of choosing his particular missions, especially in wartime, and Yadin was quoted as saying the Army had no choice but to discharge Geva "even though there might be sympathy for the courage of an officer willing to sacrifice his entire career for his convictions."

When he was 27, Geva became the youngest colonel in the Israeli Army. His brigade was one of the leading units in the Israeli sweep up the Lebanese coast in the first days of the war. The men Geva commanded are now on the outskirts of Beirut, awaiting the outcome of the negotiations over the fate of the trapped PLO guerrillas.