AT THIS DELICATE moment in the Mideast, Sen. Frank Church (D-Idaho) suggests, the United States ought to "review" all prospective new arms transfers to make sure they don't complicate the region's quest for peace. It's a good idea. To all the previous reasons for restraint, the opening of the Sadat-Begin dialogue has added a major new one. Intellectually and morally, as Zbigniew Brzezinski told National Public Radio Friday, it doesn't seem right to conduct arms transactions as though peace negotiations were not under way for the first time in 30 years.

Once this enlightened judgment has been pronounced, however, what does the United States do? For though arms may provide th resources to make war and to resist compromise, in Israel's case they can also provide the sense of security needed to accept compromise, and in Egypt's case they can give the political leadership the means to bring the military along. To alter - up or down - the large American arms flow to Israel or the modest flow to Egypt would produce political shockwaves all too likely to jostle the peace talks. Israel, of course, being so much more dependent on Washington, would suffer far more than Egypt from such a "review."

But no change of that sort can be considered in the absence of a clear showing of intrasigence. That's the time for "review," and it hasn't come yet. Until it does, Mr. Brzezinski is correct to point out that the parties have continuing military supply requirements that are "legitimate" and that do not destabilize the Mideast's existing military equation.

The prospective sale of 60 F-15s to Saudi Arabia is in a separate category. The impulse for the sale seems heavily political: For the Saudis, the planes symbolize their special place in Washington, and for the American, a "payment" for Saudi moderation in diplomacy and oil. But the impact of the sale, or so the Israel lobby here is shouting, would be heavily military. The F-15s are seen as posing to Israel a real threat in a crisis. Israelis and Arabs, both looking to victory, seem eager or at least ready for the fight shaping up in Congress over the planes.

But it is not in the American interest that the fight go on. It would only weaken the pro-peace consensus in this country and undermine the effort of American diplomacy to mediate. The administration should be looking for substitute ways to assure the Saudis of the favor they enjoy in Washington. One way to do this would be a clear demonstration that the United States was sensitive to the Saudis' concept of what would constitute a satisfactory settlement. That would eventually require, of course, further developments in the Israeli negotiating position. But softening of negotiating positions, on both sides, is what the process of peace is all about.