In THE FIVE WEEKS between beating Labor at the polls and taking office as Israel's prime minister, Menachem Begin of Likud softened his public pronouncements but he did not soften his actual positions enough to put together a broad-based government. Finally he was forced to hook up with the right-wing religious parties to assemble a parliamentary majority. It is only slight consolation that on the key issues of territory and the Palestinians, Likud and Labor are part of the Israeli consensus. In the Likud approach, there is a rigidity, born partly of ideology and religion and partly of inexperience, that is at odds with Labor's relative worldliness. The burden is on Prime Minister Begin to demonstrate that the Likud approach is not at odds with Israel's self-interest as well.

During the five-week interregnum, the United States had an important choice. It could have accepted, and thereby have helped to fulfill, the widespread expectation that a Likud government would be unable to join effectively the Carter administration's quest for an overall settlement. In that event, the administration would now be looking for ways to buy time and to string the Arabs along until a "better" Israeli government comes to power. Alternatively, the administration could have done what it actually has done: to calculate that it could not keep faith with the Arabs if it sidetracked its campaign for a settlement, and that even a Likud government is capable of perceiving the Israeli interest in joining that campaign. We think this is the wiser course. The tendency to think that diplomacy would have been duck soup if Labor had been re-elected is simply unjustified.

Vice President Mondale, in a nuanced and comprehensive speech over the weekend, signaled the administration's decision to "regain momentum." He restated the President's commitment to 1) an Israeli-type peace of confidence and contacts, 2) a return to permanent borders near those of 1967 but with special security arrangements for Israel in the interim and 3) "some arrangement for a Palestinian home-land or entity -- preferably in association with Jordan." In bold bids for Israel's cooperation, he promised that the United States would "not use military aid as pressure," and he held out the possibility of face-to-face talks with the Arabs at Geneva later this year.

In brief, the Mideast is now on notice that the United States will try to help Israel achieve precisely that neighborly relationship with the Arabs that Israelis have always described as their collective heart's desire; "some progress" has already been made toward that goal, Mr. Mondale said. The price is, of course, accommodation on territory and on the Palestinian issue. Simultaneous, measured movement toward both sets of goals is the essence of American policy. We agree with the administration's judgment that it is premature, not to say dangerous, to assume that either the Israelis or the Arabs cannot move along that path.