The United States has been committed for more than 30 years to safeguarding Israel's existence. Hence there is no security reason why it was necessary for the US and Israel to conclude a formal agreement of military cooperation. This agreement, the so-called memorandum of understanding on ''strategic cooperation, '' may indeed fit in with the Reagan administration's plans for building up a kind of collective security system against Soviet expansion in the Middle East. But it seems to have been dictated largely by the need to soothe mounting Israeli anxieties in the wake of new US policies - including the sale of AWACS jets to Saudi Arabia and a cautious nod of approval to the Saudi peace plan.
The Israelis appear to have pushed for the agreement against the background of US reluctance to go too far with a formal military arrangement. It is hard not to notice, for instance, that Israel raised strong objections to the inclusion of European nations in the Sinai peacekeeping force which the US is putting together at the very time that Israeli Defense Minister Ariel Sharon was arriving in Washington for talks on military cooperation. Israel has yielded on the Sinai issue, and a draft joint statement on a Sinai multinational force and the US-Israeli accord on cooperation seem to have come virtually at the same time. Whether this is coincidental or not, it is no secret that Israel seeks closer military ties with the US and feels all the more secure whenever the US puts its signature on a document increasing its concrete involvement in the area.
Many Americans, while friendly to Israel, may be concerned that the new agreement binds the US too closely to it. They should be assured that it does not constitute a formal alliance. These points in fact can be stressed:
* The agreement is not a mutual security pact.
* It limits US-Israeli cooperation to defensive measures against the Soviet Union. The two sides even made a point of stating that the accord is not directed against any Arab state or group of states in the region.
* It orients joint military cooperation to areas in and around the Mediterranean rather than east toward the Persian Gulf.
* No US commitments were made to store tanks, planes, and other heavy arms in Israel, something the Israelis favor but which Pentagon officials are wary of. Detailed arrangements for joint maneuvers are deferred until separate talks - and only naval and air exercises, not ground maneuvers, are specified.
While Israelis may be bothered by some of the vague language in the memorandum, the generalities are prudent where Washington is concerned. It goes without saying that the United States cannot act as a credible mediator of the Arab-Israeli conflict if it formally aligns itself with one party to the dispute. Even while continuing to provide massive aid for Israel's defense requirements, the US cannot lock itself into an inflexible relationship with Israel. To achieve a comprehensive peace settlement enhancing the security of all states in the region - a settlement which in itself will do much to neutralize Soviet influence - it must retain its freedom of action.
President Reagan has rightly recognized Israel as a strategic asset in the Middle East. If the Russians or their surrogates ever were to make a lunge in the region, the military prowess of the Israelis would be a formidable defense. But Mr. Reagan must know, too, that the US can be effective only through balanced diplomacy. It is extremely important that the new military agreement with Israel not become the opening wedge of a formal commitment of American forces to Israel's security whatever the circumstance. This would risk undermining the prospects for peace.