The anguish of American Jews torn between their dedication to Israel and their dismay at the Begin government's invasion of Lebanon was summed up in one emotional session last night of the nation's Reform rabbis' annual convention.

At issue was the Central Conference of American Rabbis' traditional pronouncement on Israel. The dilemma: whether to go public with the concern over what many feel to be the betrayal by Prime Minister Menachem Begin's government of Judaism's basic concepts of justice and the sacredness of human life, or avoid giving comfort to Israel's enemies at this time and adopt a resolution justifying the military action in Lebanon as necessary to protect Israel's border communities.

In the end, the second option won, but the emotional debate over the issue reflected the pain and ambivalence some Jews feel over the news reports from Lebanon these days.

Rabbi Roland Gittlesohn of Boston, still bleary-eyed from the jet lag of his most recent trip to Israel, succinctly stated the question. "Was Israel right in pushing . . . beyond its 40-kilometer objective?

"I don't know," he said. I have been among Israel's severest critics . . . I have criticized Israel in the past and I shall criticize again -- but not now, my friends, not now. Not now. The house is on fire and my brothers and sisters whom I dearly love are in that house . . . For the sake of Zion, I will hold my peace."

"Over and over" countered Rabbi Jerome Malino of Danbury, Conn., "We are told 'this is not the time to criticize . . . 'There are times when we must speak what we know to be right irrespective of the prevailing circumstances."

Rabbi Robert Marx of Chicago offered a resolution that said the "the tragic loss of human life and the tremendous destruction of property" in the Lebanon war, leave us concerned, not only for the people in Lebanon but for the soul of Israel and the Jewish people . . . The current Israeli leadership interpreted American Jewish support for Israel as support for its policies in Lebanon. This is not so."

Rabbi Herbert Rose defended the Begin policies of driving the Palestine Liberation Organization out of Lebanon. "Our philosophy in Judaism is not to turn the other cheek for evil," he said, "but to strike out at evil and cut off its arm."

Rabbi Everett Gendler of Lowell, Mass., said the criticism of Israel was offered "in a loving spirit. It is wrong that we have confused moral principles with the politics of a given nation-state. If we can't articulate" Jewish principles in criticizing Israel, "what do we do to Jewish credibility 10 years from now, 20 years from now?"

Rabbi Stanley Davis of Worcester, Mass., reminded the group that "This resolution is not just going to be read by Israelis . . . It will go to Congress . . . It will influence funding . . . "

The critical resolution was defeated by what appeared to be a 2-to-1 show of hands. Shortly before midnight, in a voice vote, a resolution was approved denouncing "acts of violence" by the PLO, which forced Israel "to respond so as to secure its towns and villages from bombardment and terrorist infiltration." The resolution went on to lament "the tragic loss of life on all sides in Lebanon" and urged a negotiated settlement to the conflict.