Could we now have, please, a new definition of a "moderate Arab"?

Crown Prince Fahd of Saudi Arabia has just blown the title the administration pasted on him during the recent bone-breaking AWACS debate.

By the time his royal highness stood up to show his stuff as a peacemaker, he had raised the price of oil, which was, of course, precisely the kind of reprisal we had been warned to expect if we did not sell him the planes.

That was a detail the Reagan White House brushed aside in its mad rush to don burnooses in its enthusiasm for the new friends, on whose behalf several senatorial reputations were lost.

The prince, who runs the Saudi government, held a "dialogue" Monday in Riyadh with a groveling scribe who seemed stunned at the honor of asking questions. You might have thought, from the imperial tone of the royal remarks, that the prince had not won a victory in the U.S. Senate but had conquered us in war, and was dictating the terms of surrender.

His highness made Menachem Begin, hitherto widely regarded as the most trying leader in the Middle East, look like a model of moderation.

It was, you remember, last Thursday when the president broke out the champagne in jubilation that we had passed the litmus test set for us by the House of Saud.

In Monday's "dialogue," Reagan's hard-bought new ally was giving him in Arabic the old query of the ungrateful constituent: "What have you done for me lately?"

It was nice of the president to sell him the AWACS planes, the prince said patronizingly. His salaam was accompanied by a swift kick in the teeth.

"We in Saudi Arabia greatly appreciate the steadfastness of the administration in confronting the Zionist pressure groups which waged a vicious, desperate battle to prevent passage of the deal. This is proof of the adage: where there's a will, there's a way," he said.

To sell Saudi Arabia the planes, however, was not enough. Now we must buy the Saudi peace plan. It is the new litmus test we must pass.

"What is now required from the present administration," the prince informed us, "is to start the bigger and more important battle it must wage in order to establish just and comprehensive peace."

The president, in the first fine, careless rapture of the victory in the Senate, had spoken effusively of the Saudi plan, in which he alone, it should be added, saw "for the first time . . . recognition of Israel as a nation."

Nothing in the prince's "dialogue" suggested any such thing. It was cast in such coercive, militaristic terms as to indicate that the one recognition to be afforded Israel will be the right to allow itself to be driven into the sea.

Prince Fahd spoke at one point of the need to "force" Israel to "accept the Saudi peace principles." At another, he mentioned "mobilizing . . . all Arab potential and energy and deploying them in the service of the targets we seek."

The prince approves of the recent Soviet upgrading of diplomatic recognition of the Palestine Liberation Organization, Israel's nemesis. He calls "Brother Yasser Arafat" the "basic numeral in the Middle East equation."

Israel seems to have no part in the equation, seems to be expected to give up Jerusalem to the PLO.

The Reagan administration came out of its infatuation with this desert Metternich to announce Monday that it had been misunderstood. The president actually is much in favor of the Camp David accords. The prince said Camp David is dead.

Reagan's first Arab visitor since the AWACS sale was King Hussein of Jordan, who also made no grab for the healer's mantle. At a Capitol Hill lunch, he told senators that Israeli "intransigence" had been a contributing factor to the tragic death of assassinated Egyptian president Anwar Sadat.

Too much, obviously, was expected of the Saudis by Reagan.

From the beginning, Reagan brushed aside the question of whether we had set about creating another Iran. He wouldn't let it happen, he said flatly. He didn't say how.

There are differences, none of which is reassuring. Iran had a 50 percent literacy rate. Saudi Arabia, with a population one-fourth that of Iran, has a 15 percent rate. The late shah had a standing army numbering 415,000. Saudi Arabia has 45,000.

But we go on forming a beautiful friendship. Saudi Arabia is advertising for U.S. personnel, for hospital administrators and computer programmers who, it is hoped, will not become tomorrow's hostages.

Meanwhile, the job of "Arab moderate" remains unfilled. If Prince Fahd is an example of the reasonableness, tact and understanding in our new "island of stability" it will be empty a long time.

The big difference between the prince and the shah is that the shah was easier to get along with. At least he just bought our weapons and spared us his "peace plans."