The presence of Israeli troops in Southern Lebanon is a preventive, not a retaliatory action, Yehudah Blum, Israeli Ambassador to the United Nations, said last night at the Law School Forum.

Calling the Israel Defense Force's presence in Lebanon "a limited operation," Blum said its goal is to preclude any further possibility of terrorist acts from that area. Monday, Palestinian Liberation Organization (PLO) terrorists attacked Kibbutz Misgav Am, killing three Israelis.

The Israeli government received information that the PLO timed its Passover attack on the border kibbutz to coincide with and disrupt the ongoing peace talks between Israel and Egypt, he said.

Southern Lebanon has been the PLO's base of operations since 1970, when King Hussein of Jordan forcibly expelled the group from his country, the ambassador added.

Blum said the PLO's strong anti-Israel position is evdenced in its. "Three Stage Plan," introduced in 1974. The plan initially calls for a mini-state in the lands now occupied by Israel, then Israel's return to the borders outlined in the U.N. partition plan of 1947 and, finally, a "democratic secular state in all of Israeli held Palestine."

"We see not reason to oblige them in this plan," Blum said, adding that a return to the pre-'67 borders, which would leave Israel with a breadth of less than eight miles in her most populated region, would be "sheer insanity and suicide."