At a private meeting June 10 in Manhattan's plush Harmonie Club, 18 prominent Jewish leaders whose common bond is Ronald Reagan sped up the mad chase for the Jewish vote by all parties in 1980, a pursuit menacing U.S. policy in the Mideast that could lead to drastic breakaway action by Israel.

The meeting, presided over by Los Angeles businessman and longtime Reaganite Albert A. Spiegel, poured over data and intelligence for eight hours. Their conclusion: Reagan could win over 40 percent of the Jewish vote, enough to elect him president. Jewish trust in President Carter has been destroyed, said Spiegel.

Those blue-sky prospects mean there is slight chance that either Reagan or independent candidate John Anderson would seriously protest any adventurous excesses by Menachem Begin's Israeli government between now and Nov. 4. Furthermore, it is Begin's alienation from President Carter that makes the rush for the strategically placed Jewish vote so frenetic by all three candidates.

The early stage of this rush has damaged U.S. efforts to solve the Arab-Israeli struggle. Some officials believe it may stimulate dangerous Israeli action -- perhaps another military invasion of Lebanon -- before the election.

Paying court to the Jewish vote during presidential campaign seasons has never before reached the peak of these early 1980 maneuverings -- including the liberties Carter has given Vice President Walter Mondale, his chief political surrogate. In a recent New York speech to the National Council of Young Israel, Mondale said that "we support the right of Jews . . . to live anywhere they choose to live, including the West Bank."

That might seem to collide with Carter's much-advertised opposition to Jewish settlements on the West Bank, which he calls illegal and an obstacle to peace. Mondale avoided the word "settlements," but to the foreign ministries of Saudi Arabia, Egypt and other moderate Arab states, the distinction is a blur that raises questions about Carter's credibility.

Saying that Jews could live anywhere on the West Bank they wanted brought sustained applause for Mondale, but the anti-Carter animus of the American Jewish community is not about to dissipate because of such political ploys. The upbeat mood at Spiegel's pro-Reagan planning session stems from the belief that Carter is perceived by many Jewish voters as a threat to Israel's future.

Cashing in on this distrust, Reagan has gone to ludicrous lengths to defend his own integrity with American Jews. He denied he had told Egyptian Ambassador Ashraf Ghorbal that, if elected, he would seek "a comprehensive peace settlement" -- which to many American Jews connotes giving up the West Bank.

Public opinion polls show Anderson's standing with Jews to be extremely high, and he aims to keep it that way. He has directed his agents to tell Jewish leaders that former undersecretary of state George Ball, Anderson's earliest foreign policy adviser, will not be allowed to advise him on the Mideast. Within the American Jewish community, Ball is despised for alleged bias against Israel.

U.S. officials think this political climate spurs Israel into making new demands and contemplating new military ventures. Agriculture Minister Ariel Sharon, one of Begin's closest confidants and chief strategist for Israel's settlements policy, last month publicly recruited Orthodox Jewish youth in New York to come to Israel and help settle the West Bank.

Speaking to the Union of Orthodox Jewish Congregations of America, Gen. Sharon called on his audience to "send groups to Judea and Samaria, even temporarily, as a symbol." One Carter political adviser told us that recruiting Americans to fulfill an Israeli policy that President Carter calls "illegal" could not have happened in a non-election year.

The Jewish vote is too valuable for any presidential candidate to rise above, and that is particularly true for Reagan. Concentrated in a few large states, it could swing the balance.

With such a glittering target, Carter, Reagan and Anderson will not limit their promises to Israel. However much that tempts Israel between now and the election, it will not make any easier the hard decisions concerning the Mideast required of the man who takes the oath next Jan. 20.