It has been said that mankind hopes vaguely but dreads precisely. Israel has had more reasons for dread than for hope. But rational prudence may be disappearing, replaced by reflexive negativeness in the current Israeli government.

The government is characterized by a lack of subtlety, a lack that has until now characterized Israel's enemies, often to Israel's advantage. Israel's government is forfeiting a chance to shape to its advantage a debate that it cannot prevent.

The debate about President Reagan's peace proposals can begin with this fact: Jordan is, historically and ethnically, a Palestinian state, and any renewed "association" with a West Bank entity will make Jordan even more Palestinian. King Hussein -- a Hashemite, not a Palestinian -- may be ambivalent about re-acquiring responsibility for the territory he lost in 1967.

But whatever Jordan's Palestinian complexion, it does not mean that the Hashemite dynasty is less than legitimate. George I was England's legitimate sovereign, and he was as German as sauerkraut and deaf as an adder to the English language. Israel's defense minister, Ariel Sharon, says: "The Greeks went looking for a king and they chose an English-German one. So why shouldn't the Palestinians keep a Hashemite king?" Indelicately put, but a good question.

Reagan's plan will die in the cradle if Hussein continues his un-kingly obedience to the decision of Arab powers at Rabat in 1974 declaring the PLO the sole legitimate representative of Palestinians, the largest block of whom are Hussein's subjects. Israel should refuse to participate in any process that allocates any role to the PLO, about which Reagan said two years ago:

"(The PLO) represents no one but the leaders who established it as a means of organizing aggression against Israel. The PLO is kept under tight control in every state in the area except Lebanon, which it has effectively destroyed. . . . The PLO has murdered more Palestinians than it has Israelis."

Actually, the PLO also represents, in addition to its Soviet sponsors, its Arab -- principally Saudi -- benefactors. Reagan's administration manifestly has a soft spot in its heart, not to say its head, for the Saudi regime. Reagan's proposals will test his administration's hypothesis that the Saudi regime, contrary to all the evidence that it is rickety and radical, actually is stable and constructive. The plan really requires Saudi support, political and financial, for Hussein to take his proper responsibility for the Palestinians.

There are limited and, over time, declining benefits from tracing far back the roots of historical controversies. But because the Saudi and Jordanian regimes have been so sniffy about the legitimacy of the state of Israel, it is useful to note the following.

Jordan is a somewhat jerry-built nation, improvised relatively recently, but the Hashemite dynasty is ancient. It ruled Mecca and Medina for many centuries, until its place was usurped in this century by Saudis. The Saudis do not expect the Hashemite elite to return whence it came, and neither the Hashemites, who have put down roots in Palestine, nor the Saudis should pretend they expect Palestinian refugees to return to Palestine's coastal plain, to Tel Aviv and Haifa.

Hussein's attack on Israel in 1967, which cost him control of the West Bank and part of Jerusalem, was not just unprovoked; it came after Israeli assurances, through the United States, that Israel would not attack if not attacked. But Henry Kissinger, writing of Hussein, says of 1967: "Though (Egyptian President Gamal Abdel) Nasser had treated the (Jordanian) Kingdom with aloof disdain, Hussein carried out his high conception of the requirement of Arab solidarity and entered a war that Nasser had already lost."

That is an interesting ascription of moral weight to Hussein. For years it has been said that Jordan was not weighty enough to be the first neighbor to make peace with Israel, but that it must be the second. Writing about Hussein's position as it was a decade ago, Kissinger says Hussein "was trapped in the paradox that he was the Arab leader most ready to make peace, yet of all the territories it had conquered, Israel was most reluctant to relinquish the Jordanian portion, which it most intimately connected with its own tradition."

Reagan's proposals will test not only the administration's cheery assessment of the Saudis, but Kissinger's kindly assessment of Hussein. At least the proposals will test these hypotheses if the Israeli government can regain its composure and show the political flair that has been as important as military virtuosity in preserving Israel as an embodiment of intelligence and bravery.