ISRAEL'S NUCLEAR CHARADE

A dark nuclear charade is playing out in Jerusalem. On the surface, it is about the former nuclear technician who is on trial on charges of telling a British newspaper that Israel has built and stockpiled 100 or more nuclear weapons. The defendant, Mordechai Vanunu, managed to smuggle out a message that he had been kidnapped in Italy by the Israeli secret service. Israel appears to be getting the worst of two worlds. After all its nuclear denials, it is being shown in a fashion to be a nuclear power, and after all its democratic professions, it is coming through as a country that cuts the corners of the law.

These, however, are workaday embarrassments, and Israel can endure them, though not without cost to image and morale. There is something far more important, and not only to Israel. The Israelis, who have been doing their nuclear work in some secrecy over the decades, have made the portentous decision to notch their program far forward into public view. They have decided they have more to gain than lose by adding the confirmatory official weights of arrest, announcement and trial to what otherwise might be treated as the unsupported allegations of a lone bad apple.

A country's statements about its nuclear intentions can never be casual. The ostensibly non-nuclear countries, especially those like Israel which are formally at war with powerful neighbors, have special requirements for political nuance. The statements they make and the impressions they contrive bear directly on the plans they and those neighbors and their respective patrons and other countries in the neighborhood must make about the most fundamental matters of war and peace.

Sensitive to international apprehensions, the Israelis have always tucked their nuclear program behind a public pledge not to be ''the first country to introduce nuclear weapons into the Middle East.''

''Nor,'' now adds an Israeli who I think is in a position to know, ''the second.''

This is one pungent expression of Israel's decision to start leaving the plateau of ambiguity and deniability, where its nuclear program has rested for many years, and to move on to the uplands of virtual public acknowledgment. The move will force everyone to calculate that the next war in the Middle East may have more of a nuclear dimension than the last one. Knowing that the Israelis have gone to a new nuclear posture, others will have to figure . . . But you get the idea. Everything starts to shift. The terrible but, in a sense, knowable formulas of conventional war merge into the more terrible and less knowable equations of, at the least, the implicit brandishing of nuclear arms by Israel.

In fact, the last Mideast war, in 1973, did have a nuclear dimension, involving first a feint by the Kremlin to demonstrate fidelity to its failing Egyptian clients and then a set of signals in response by the United States. There has been a quiet conspiracy since to keep a lid on the affair. The great powers are perfectly willing to advertise their reliability as patrons, but they are properly nervous about advertising their availability as nuclear guarantors. This is serious stuff.

Why now would Israel care to change the rule of nuclear discretion? On a philosophical level, it is evident that Israel, a state born from a historical encounter with doomsday, seeing the tide of military technology rising everywhere in the Middle East, craves the symbols of ultimate protection and self-reliance. On more of a working level, Israeli strategists perhaps calculate that hardening the country's nuclear posture will narrow the zone in which its enemies might somehow miscalculate its resolve, or that it will -- the catchall explanation for every military ratcheting -- ''strengthen deterrence.'' Or do they figure that things were moving that way anyway and that the Reagan administration's immense favor for Israel provided the best possible political window to break toward the nuclear light?

For the United States, there is one overwhelming policy implication: to stop its cautious little throwaway diplomatic time-wasting exercises and to commit itself with Carter-like intensity to the search for an Israeli-Palestinian settlement. The alternative is to sit around until Israel, in its frustration, elects an Ariel Sharon, the sort of man who could put America's loyalty to Israel to a test that no responsible American leader could want to pass.

"Israeli strategists perhaps calculate that hardening the country's nuclear posture will narrow the zone in which its enemies might somehow miscalculate its resolve."

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