It is not hard to understand why the Reagan administration's decision to "suspend" the brand new U.S.-Israeli memorandum of understanding (MOU) on strategic cooperation was particularly enraging to Prime Minister Menachem Begin. While the MOU fell far short of what Begin wanted, it served as a symbol, at least. As an American diplomat put it, "It elevated Israel from the status of a dependent to that of an ally."

But to understand the explosion of invective from Begin's minister of defense, Ariel Sharon, you have to realize what strategic cooperation with the United States means to the man who does the big strategic thinking, with Begin's blessing, for the Israel government. And that requires careful consideration of an extraordinry public document that by happenstance received little notice outside of Israel.

It was to have been a paper to be delivered by Sharon at a conference last month at the Institute of Strategic Studies at Tel Aviv University. When the defense minister was unable to be on hand he tried to have it read for him by Maj. Gen. Yariv, a former head of military intelligence. Yariv says he didn't think that would be "appropriate." Left unsaid was that, on the whole, he disagreed with it. The paper was rescued for posterity by subsequent publication in a local newspaper, but its immediate implications are profound.

Entitled "Israel's Strategic Problems in the '80s," it outlines a policy that stretches Israel's "sphere of strategic and security interest" from Pakistan, Turkey and Iran across the Arab world and deep down into central Africa. It would commit Israel to military interdiction of any mass movement of military forces from one Arab country to another in a way that seemed to threaten Israel.

With the bombing of Iraq's nuclear reactor presumably as a model, it also would commit Israel to preempt access to nuclear weapons, not just by neighbors, but by any "potential confrontation state. . . . We shall have to prevent such a threat at its inception."

All this, and more, Sharon's Israel would undertake in the name of a "fruitful and mutually beneficial security relationship with the United States."

His institute paper, moreover, may not even do full justice to his grand design. Associates describe a military role for Israel as a "surrogate" rapid deployment force for the United States, conveniently on the scene, the first to arrive to counter Soviet- instigated threats to stability from the heart of Africa to the Persian Gulf--America's "Cubans" if you will. They speak of massive Israeli investment in research and development in order to counter qualitatively--with high technology--the quantitative edge of Israel's enemies.

Already the principal supplier and financier of the Israeli military establishment, Washington would have to bankroll still more of it for Sharon to fulfill his dreams, and the current post-Golan climate is hardly congenial to more support.

As a case of reach exceeding realistic grasp, the Sharon plan is, well, astonishing. But it is even more significant as a measure of just how widely American and Israeli conceptions of each other's roles and missions have parted company. Even the watered-down MOU, now on hold, was resisted by those in the Reagan administration whose priorities lie with the nourishing of strategic relations with Egypt and the Arabs of the Persian Gulf.

Yet to Sharon, the MOU constituted no more than the thin edge of a wedge to open up a far wider and deeper U.S.-Israeli defense relationship--"a new starting line."

"Because of the nature of the military forces of today, which are highly mobile armored and mechanized forces," the defense minister argued, "and because of the range of weapon systems in the Arab order of battle, including missiles and intelligence means which cover the whole of Israeli territory, we face on our present borders the very same defense problem we had on our 1967 lines."

Now that seems to say that Israel cannot afford, for security reasons, to surrender sovereignty over the remaining occupied territories-- other than the Sinai, which passes back to Egypt next April, barring some mishap. And elsewhere in the paper, Sharon pretty much says it.

So much for the Camp David framework--and for the "autonomy" process on the West Bank and Gaza, to which the Israeli government regularly reaffirms its commitment, and for which Menachem Begin takes great pride of authorship.

Of Ariel Sharon it is variously said that he is "tough . . . determined . . . dangerous, but no fool." It's agreed he has considerable influence, strong support--and more than his share of political enemies. But he is high on everybody's list of future Israeli prime ministers.

So his big dreams for Israel and for a grand U.S.-Israeli alliance, while they may be non- starters in the present scheme of things, cannot be lightly dismissed. At the very least, they suggest just how far apart the United States and Israel have been carried in their sense of common purpose by the surge of events, conflicting interests and internal politics.