IT WAS NOT enough for Menachem Begin to express his immediate and complete disagreement with President Reagan's call for a freeze on settlements in the West Bank. His Cabinet promptly went on to fund three new ones and approve plans for seven more. But no one should be surprised by this sequence. Everyone in the Mideast had expected the Israeli government to test Mr. Reagan's seriousness, and this is one important way it is being done.

We liked the administration's response. It was done not by arm waving or personal attacks but by underlining the principles of the president's policy and by touching the questions that Israelis are now starting to review. Does Israel by its settlements mean to frustrate the "broader participation in the peace process" that it is precisely the American purpose -- and Israel's Camp David obligation -- to encourage? Is Israel backing off its commitment to United Nations Resolution 242, whose promise is that in the West Bank, as on Israel's other fronts, territory acquired in 1967 will be exchanged for peace?

No one should imagine, however, that the Begin constituency or the Israeli people as a whole will be swayed strictly by reasoned argument. How, then, will it happen? Not so far in the back of the minds of many people is the thought -- a fear or a hope, as the case may be -- that sooner or later Mr. Reagan must get tough with Israel and threaten either to cut off aid or even to abandon the country altogether. Nothing the United States can now say or do will totally banish that specter, but it is good to see the secretary of state trying all the same.

Mr. Shultz maintains that it will be Israel's emerging sense of the benefits of the Reagan proposals, rather than any direct sanctions, that will bring Israel around. This is, tactically and morally, the right point of view. It is bound to disappoint those who have come to feel that only by a kind of political Armageddon, an ultimate showdown, can the American view prevail. But it is the only way a country like the United States can go.

The very idea of abandoning Israel is offensive and harmful. If the notion got a foothold, it would strengthen the tendency to rigidity already amply evident on the various sides. It suggests a basic incompatibility between American and Israeli interests. It suggests that Israelis are more devoted to expansion than peace, and that Americans are casual in their regard for Israel's well-being. None of this is true.