In a further effort to get at the fundamental, debatable differences between the two leading presidential candidates on foreign policy, turn now to the Middle East -- torn by conflict, contradictions and confusion, and more than ever unpredictable. And yet the current chaos actually serves to sharpen the choice for voters. Where else around the world will the outcome of the presidential election have so instantaneous an impact on policy and events? tConsider how the state is set:

Jimmy Carter's Camp David process, for whatever one may think of its promise, is on a loose hold, although ministerial-level talks on its next phase -- autonomy for the Israeli-occupied West Bank and Gaza -- are resuming. If Carter is reelected, they will almost certainly pick up rapidly. A U.S.-Israeli-Egyptian summit is penciled in for later in the year.

The Carter administration firmly believes that continued progress on this front is central to the question of how to deal with the other large part of the Middle East problem: the West's potentially crippling, life's blood reliance on Persian Gulf oil. Not that a resolution of the Arab-Israeli-Palestinian conflict would solve everything. But while it remains in stalemate, it makes it a lot harder for the United States to work constructively with the Persian Gulf Arab states, for example, on the sort of joint defense measures -- base rights, stationing troops, prepositioning of supplies -- that might help make the oil supply more secure.

If Ronald Reagan is elected, the Carter stage-setting obviously goes by the board. This isn't to say that Reagan couldn't pick up the Camp David process early next year. But 1981 is Israel's turn to have an election. "So we're probably talking about a delay of maybe a year and a half," says one reasonably non-partisan expert here, "if we're talking about Camp David at all."

And that's just it. In all probability, if Reagan is president we won't be talking about Camp David, and not just because of a new president's traditional reluctance to build on a predecessor's monument.

From all the available evidence, Reagan doesn't believe much in Camp David. He doesn't see anything like the tight connection that Carter sees between safeguarding the oil flow and making some headway in resolving the Palestinian issue. He sees as "zigzags and flip-flops" the necessary ambiguities in America's role as honest-broker in the Palestinian conflict.

He sees United States pressure of any kind on Israel as a threat to Israel's and our own security. And that is because, first and foremost, he sees Israel "as a major strategic asset to America" in a struggle in the Middle East that is essentially between East and West.

This is not a question of relative decibel levels of devotion to Israel in an election year. Both Carter and Reagan share the same sense of an American moral obligation to Israel's security and of the need to protect the best interests of the United States as well as Israel.

The point is how they would go about it.And the difference is enormous, if only because the two men see the problem in profoundly different ways.

"The paramount American interest in the Middle East is to prevent the region from falling under the domination of the Soviet Union," Reagan once wrote. Israel, he went on, is a "military offset to the Soviet Union." Thus, to push unpalatable terms on Israel for a West Bank agreement, for example, is not to encourage resolution of a dangerous conflict -- for Israel -- but to weaken West against East.

Reagan would do just the contrary. He's talked repeatedly of a joint military partnership between Israel and the United States (and perhaps even Egypt) -- a pooling of resources and facilities, even joint command. But what Soviet acts would this collaboration deter? More specifically, how would it guarantee the pumping and transit of petroleum, nip an unwelcome revolution in the bud, interdict the smashing of oil installations by an Iraq and an Iran at war, or make Israel measurably safer from its worst Arab enemies?

As for the American mediator's role in the Arab/Israeli conflict -- a matter of some importance to Israeli security -- how would you reconcile that with an active, tight, U.S.-Israeli military partnership?

Reagan, in short, would reset the stage, rewrite the script, recast the leading actors, dramatically. Carter would let the Camp David process play on. Here again, there's a clear choice, worth talking about.