LEAVING THE EUROPEANS aside, the lessons of Lebanon appear so far to have been learned largely by the American public. The president continues a policy that does not serve U.S. interests. Israel acts as if it has a God-given right to kill Palestinians and their national aspirations. If the Palestinians have learned that peace with Israel even on reasonable terms would suit them, they are saying little about it.

Yet among Americans, outrage at events in Lebanon is widespread, and polls, editorials, letters, articles and advertisements show that Americans realize that satisfying Palestinian national aspirations is as necessary to peace as assuring Israel's security.

It is from this public realism that the "opportunity" comes for peace between the Arabs and Israel. The president and his new secretary of state can now formulate an effective peace policy. But first the president needs to free himself from several misconceptions.

He must disabuse himself of the Israel- born notion that "one has to differentiate between the PLO and the Palestinians." The PLO leads Palestinian nationalism. He must learn that the United States has nothing to gain and much to lose from his intended return to the Camp David autonomy talks. The talks will be long resuming.

If resumed, Israel does not intend them to produce what it invaded Lebanon to prevent: Palestinian self-determination on the West Bank.

Israel will continue to manipulate the Camp David accord for its own ends. Indeed, a convincing argument can be made that Israel has abrogated Camp David. It has said that it will never relinquish possession of the West Bank, and it has unilaterally redefined the word "autonomy" in the agreement to this end. It is attempting to create a quisling government over a subject people on the West Bank. And it is trying to destroy Palestinian political power in Lebanon. The United States cannot hold Israel to the letter and spirit of the agreement because Israel would escape through loopholes in the text.

For America to have an effective Arab-Israel policy, the president would have to "transcend" Camp David, to use a popular euphemism, and institute a peace process that could be controlled from Washington, not from Jerusalem or Arab capitals. This would mean doing what previous administrations have considered doing but not done, partly because of adverse circumstances and largely from lack of wisdom and courage. It would mean:

* Putting forward a U.S. peace plan.

* Talking directly to the PLO.

* Using enough leverage on Israel, the Palestinians, and Israel's eastern Arab neighbors so that they negotiate a peace treaty and abide by it.

Previous administrations have shied from putting forward a U.S. peace plan because they believed a peace treaty would be viable only if it resulted from the initiative of the parties and because Israel would charge that a plan would undercut Israel's negotiating position. Always of limited validity, these reasons have no validity today.

The two sides are so entrenched in their positions that only the United States can shake them loose. And Israel is no longer negotiating. It is imposing its own policy of lebensraum.

The U.S. peace plan should include the principles and formulas for all aspects of a just, fair, and comprehensive peace. It should be base on United Nations Resolution 242's basic trade-off of territory for peace and the mutual right of Palestinians and Israelis to self-determination and security, and it should include the international and on-the-ground safeguards to sustain peace. The plan would also provide for normal political, cultural, and commercial relations.

The administration would publicize the plan widely and vigorously. Then the parties would be given only a brief period to subscribe to it and a slightly longer time to negotiate the details of a treaty. The implemention time should also be short, except for the provisions normalizing relations, because a long transitional period would allow opportunities for hardliners and for the unpredictable to upset the agreement.

The world rightly insists that the PLO, as the Palestinians' voice, acknowledge Israel's right to a secure existence. Yet, not talking with the PLO is a dangerous absurdity for the United States. The PLO has not been allowed to join in past negotiations despite its desire to, so its intentions have not truly been tested. Calls for the PLO or Israel to make the first gesture toward the other have proved fruitless. The United States must talk with the PLO to obtain its adherence to a peace plan and to lead the PLO to constructive treaty negotiations with Israel.

Abba Eban had the right idea years ago, although his theology was weak, when he said that peace between the Arabs and Israel would not be achieved through "immaculate conception." Henry Kissinger's mistaken promise to Israel in 1975 that the United States would not negotiate with the PLO until it recognized Israel's right to exist can be dispensed with in either of two ways: as invalidated by Israel's rejection of Resolution 242 and abrogation of Camp David or as a constructively ambiguous statement that allows us to talk with the PLO so that it will negotiate with Israel.

To Americans, using leverage on other nations connotes arm twisting and nastiness. Toughness is a necessary part of leverage, but forcing a sovereign nation to accept U.S. dictates is difficult to impossible -- short of defeating it militarily. Effective leverage, therefore, lies as much as possible in inducements, as little as necessary in punitive pressures. The positive benefits of cooperation with the United States, added to the costs of noncooperation, should yield a sum that is persuasive.

The Palestinians woulddwelcome a just U.S. peace plan, because it would call for self- determination for Palestinians living in the West Bank and Gaza (certain to result in a Palestinian state), recognize them as an equal party in the peace process, and establish the PLO as their representative in negotiations.

The "rejectionist" factions within the PLO would denounce the plan for its guarantee of Israel. There would be some division among Palestinians over the PLO's leadership role in the new situation and a bitter struggle for power within the PLO. (It is frequently so when rebel nationalists gain power -- witness Africa today or Ireland after 1919.) But having the promise of a state, moderate Palestinians with the help of Arab governments could subdue dangerous challenges, although not without bloodshed.

The Arab governments, with few exceptions, would consider a just U.S. peace plan a major breakthrough for their interests. It would promise a treaty that would protect them from Israel and focus Palestinian nationalism on a state the Arabs would intend to control. It would lessen the fear of being out-negotiated by Israel, which has in the past helped prevent them from talking peace. The United States could further sweeten the deal with large offers of assistance to spur Arab economic and social development.

Obviously, not everything in the peace plan would please the Arabs and Palestinians. Treaty negotiations would be very difficult on issues like Jerusalem.

The United States would have to exert leverage, which likely would evoke counter- leverage, particularly from the Arab oil states. Were the Arabs as unwilling to make peace with Israel as they were before 1967, and were the Palestinians as strong as they thought they were a month ago, the danger from counter-leverage would be higher. Weighed against the danger to vital U.S. interests if peace is not achieved, proposing a U.S. peace plan would be a worthy gamble.

With Israel, the United States has to a unique degree a situation it has nowhere handled effectively: employing leverage on the government of a nation it has sworn to support. At the tactical level, the administration could decide that what is sauce for the goose is sauce for the gander: Israel has exerted great influence over U.S. policymaking -- why not the reverse? At the strategic level, when Israel's policies endanger U.S. security, as they do now, the United States is free to put its own security first. A comprehensive U.S. peace plan, however, would enhance Israel's security as well as our own. Moreover, by protecting its own security, the United States would be protecting Israel's, for Israel depends on U.S. strength, and if U.S. security is threatened, Israel's is especially so.

These would not be inducements to the Begin government. Begin would fight a U.S. peace plan with whatever weapons he could command (not excluding a military adventure to preempt the president's initiative), because he would think the plan endangered Israel's security.

Begin would be armed with the Israeli belief that Israel's counter-leverage makes it immune to U.S. leverage. He would try to fuel fears that the United States and Europe were going to let Israel down, as they have let Jews down in the past. Able neither to entice Begin with a carrot nor persuade him with a stick, and pledged to support Israel, how can the United States pursue an independent policy and propose a peace plan?

The imperfect answer is only partly that the Begin government will not be everlasting. A more important part of the answer is that moderate opinion still exists in Israel and that moderate Jews and others are increasingly speaking out for a just settlement. These moderates might well support a U.S. plan for a just and secure peace.

A U.S. peace plan would permit Israelis of whatever opinion to see rationality and consistency in U.S. policy. They could debate the known, not fear the unknown. Most important of all, a U.S. plan would test the Palestinians and other Arabs. Israelis could see their reaction to a set of peace proposals that specifically provided for Palestinian interests, Palestinian and Arab recognition of Israel's right to exist, and other safeguards for Israel's security.

The United States would explain its policy vigorously within Israel, something it has not done in the past. The president would try to shape Israel's policy with inducements, although he could never relinquish the stick, particularly to forestall an Israeli spoiling operation.

Announcement of a U.S. plan and persistent promotion of it would reassure Arab moderates, arm them against Arab extremists, and gain time for the plan to gather support in Israel. Merely to float the plan would be a repetition of the Rogers Plan, even without Henry Kissinger to undercut it. The public education effort must be followed by gaining agreement to the plan and negotiating an actual peace treaty under it.

Americans, too, need to know what their government's peace policy is so they can judge its fairness to all. And American moderates have hardliners here to contend with. Since 1967, Americans have seen only fragments of a Mideast policy, never a whole picture. As a result, ignorance and extremism have reduced the public debate to the sterile level of a U.S. policy being either "pro-Israel" of "anti-Israel." Neither U.S. nor Israeli security interests can be protected in this fashion. The debris of 15 years of this kind of "policymaking" lies all around us.

Some persons fear that a U.S.-Israel policy confrontation could arouse antisemitism in this country. Israel and some of its short- sighted supporters have fed this demon by claiming that disagreeing with Jerusalem is to subvert fundamental U.S. support for Israel and, by extension, is anti-Jewish. Equally narrow individuals on the other side have claimed that agreeing with Jerusalem against Washington is somehow un-American. Each of these charges would find less fertile ground if the American public were able to assess the fairness of the administration's total peace policy. Fear of antisemitism must not prevent the president from proposing a peace plan. Unwillingness to grapple with the possibilities must not allow this evil sentiment to threaten American society.

The president's chance to build a creative Mideast policy is that mixture of opportunity, danger, and agony of doubt of which all great choices are compounded. With a single policy he can serve the national interests of the United States and its allies, Israel, and the Arab nations.

The conditions for peace are unlikely to improve. Failure would not endanger U.S. interests more than continuing current policy. No time is perfect, but this moment is propitious.