IN THE SPACE OF TWO WEEKS, a dramatic shift has taken place in Middle East relationships that were entrenched for years.

The first move came Sept. 10 when Israeli and Egyptian negotiators settled a long-standing border dispute. The agreement immediately cleared the way for a summit meeting between Israeli Prime Minister Shimon Peres and Egyptian President Hosni Mubarak in Alexandria the next day.The breakthrough came at a time when any easing of the Mideast deadlock would have been hailed as a victory. Egypt had recalled its ambassador to Israel after the massacre of Palestinians at the Sabra-Shatila refugee camp in Lebanon in 1982. Since that time, relations between the two countries had marked time in hopes of a major initiative such as that which brought Prime Minister Menachem Begin together with President Anwar el-Sadat during the Carter years.

Once again, the risks for Egypt in the reconciliation seemed far greater than those for Israel. Already faced with isolation in the Moslem world, Egypt's position would have become instantly untenable if Israel had resorted to massive retaliation for the recent massacre of Jews at prayer in Istanbul. In this instance, Israel refrained from striking out and the new accord was preserved.

What followed could hardly have been unrelated. A surprisingly cordial meeting between Prime Minister Peres and the Soviet Union's Foreign Minister Eduard Shevardnadze marked the first high-level meeting between the countries in their history. The optimistic reports of the encounter stood in sharp contrast to the near-rebuff the Israelis suffered following initial diplomatic contacts in Helsinki just a month before.

Subtle yet equally significant change seems evident in the Soviet position in the Middle East as well. It has long been a tenet of U.S. diplomatic thinking that the Soviets have felt shut out of the Mideast peace process and so have searched for ways to invite themselves to any future bargaining table.

Normalization of any sort means recognition of Israel's right to exist, which has been the major bone of contention between Israel, its Arab enemies and the Palestinians who receive moral and diplomatic support from the Soviet Union. Any Soviet move in Israel's direction, therefore, implies a serious

break with the Palestinian cause.

This may be precisely the Soviet intention.

In the past, the Palestinian cause has had great political value for the Soviets in the Third World. The Soviet Union has provided varying levels of support to Syria and Libya, which have at the very least allowed Palestinian terrorists to operate freely. But as terrorist acts spread through Europe and Asia, the Palestinian baggage has become increasingly heavy. By all accounts, the Soviet effort to show its best face in Europe has become just as important as its image in the Third World. In addition, relations with the Reagan administration are at a crucial stage. If any evidence were to surface now that the Soviets had ever dabbled in terrorism, it might well kill any chances of a summit or agreement on a wide range of arms control issues.

If such thinking is correct, then the Soviets may be finding out what the rest of the world has known for some time. The terrorists may be easy to turn on, but they're awfully hard to shut off. Next best thing for the Soviets is to gradually but firmly distance themselves from old positions and associations. Endorse the peace process. Move toward a moderate position in the Mideast. Bargain for greater influence while trying to reassure old allies. But let the Palestinians go it alone.

These may be the signals the Soviets are sending in their new openness toward Israel. At least one shred of evidence is the massing of Israeli troops along the Lebanese border prior to the recent retaliatory forays into Lebanon.

The troop movements nearly coincided with the meeting of Mr. Peres and Mr. Shevardnadze and, while there is no suggestion that the Soviets condoned the Israeli action, presumably it could not have gone unnoticed by Soviet intelligence. Yet despite the obligatory vote of condemnation in the Security Council of the United Nations, the outcry by the Soviets seemed remarkably faint by rhetorical standards of the past.

The term isolation suddenly seems more appropriate to apply to the position of Syria rather than to the moderate stance of Egypt. Syrian President Hafez al-Assad's threat of a "stunning" response to any contemplated Israeli move into Lebanon seemed something less than stunning, stripped of the customary Soviet polemics that often accompany such pronouncements.

For the Soviets, who have just concluded a historic European security agreement with the North Atlantic Treaty Organization, the hard line seems to be softening daily on almost every front. As incredible as it seems, the whirlwind sequence of diplomatic moves has taken place in just two weeks. A

shift in Soviet-Israeli relations will serve to keep other initiatives now on track from being derailed.

If the Soviets have calculated such a shift, moderate voices in Israel and the Moslem world will be vindicated. Extremist, fundamentalist and Palestinian forces undoubtedly will suffer. The Palestinian problem will continue to hold the key to stability, but possible solutions may advance with bilateral Superpower support.

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