Israeli Defense Minister Ariel Sharon told a group of Jewish-American leaders today that Israel expects their full support as it insists on obtaining adequate "security arrangements" in southern Lebanon before agreeing to withdraw its troops from the area.

Speaking on a rocky hillside next to this five-year-old Jewish settlement in the occupied West Bank, Sharon appealed for support of Jewish Americans in pressing the Reagan administration to accept Israel's negotiating terms for a troop withdrawal from Lebanon.

"If Israel will not stand firm now, when we come to the security arrangements in Lebanon, that no terrorists will stay in Lebanon, we may come again to the same situation as we had before," Sharon said.

"It will be a major mistake after such a war, after so many sacrifices, casualties that we suffered, if we move back without solving the problem, the threat of terrorism in Lebanon," he added. "When we stand firm about the security arrangements, you must understand us and you must back us. We expect that from you."

Sharon was warmly received by the 1,000-member delegation from the United Jewish Appeal, many of whom crowded around him after the speech asking for his autograph.

The Israeli Cabinet is to meet Wednesday to put into final form Israel's demands in the negotiations for the withdrawal of Israeli, Syrian and Palestinian forces from Lebanon. The positions it adopts are expected to be conveyed to Secretary of State George P. Shultz by Foreign Minister Yitzhak Shamir when they meet Thursday in Washington.

On Sunday, the Cabinet adopted a resolution saying that "prior to the troop evacuation, security arrangements will be established which will guarantee that Lebanon will not again revert to becoming a base and launching ground for aggressive acts of hostile forces against Israel."

Israeli officials have said such security arrangements would not require the continued presence of Israeli troops in southern Lebanon, but they have never spelled out in detail what would satisfy them.

Israel would also like to see a continuing role in southern Lebanon for former Lebanese Army major Saad Haddad, whose Israeli-supplied Christian militia has served as a proxy force for Israel in the area.

The United States is unenthusiastic about any role for Haddad and, fearful that serious new fighting could erupt at any time, is pressing for a quick withdrawal agreement. These differences in approach are likely to produce specific disagreements between the United States and Israel during the negotiations, it is assumed here.

Underscoring the danger of new fighting, the Israeli military command announced that there were several exchanges of fire today with Syrian and Palestinian forces in eastern Lebanon. There were no reports of casualties.

In recent days, Sharon has accused the United States of deliberately hampering Israel's hope of attaining a peace treaty with Lebanon. But today the defense minister, who for his talk to the visiting Americans mounted a makeshift speakers' platform holding a small bouquet of flowers given him by children of the settlement, toned down his rhetoric and stressed American-Israeli friendship.

"We know that if the United States will make an effort we may be able to sign a peace treaty with Lebanon, or start a peace process with Lebanon, and soon," he said.

Sharon accused Western countries of "compromising with terrorism" and said Israel would never follow that course because it could not afford the risk.