THE UNITED STATES has been selling huge amounts of sophisticated weapons to Arab countries that have the oil wealth or the oil-wealthy friends to pay easily for them. Meanwhile, Israel has found it harder and harder to afford its qualitative military edge. Therein lies the dilemma that came to the Senate Foreign Relations Committee the other day.

In 1983, Israel will have to pay the United States $910 million for past arms purchases. Some $785 million of that will be covered by economic aid. To close that $125 million gap -- it will be more in 1984 and 1985 -- Sen. Alan Cranston urged the United States to establish the principle that new aid at least match the debt repayment.

This measure, if enacted, would relieve Israel of a large burden. But it would be an unacceptable precedent: it would put Israel alone in a category where, as Sen. Charles Mathias put it, "There would be no limit to the amount of debt Israel could absorb, because someone else is servicing the debt." One does not have to suspect the Israelis of the slightest sinister intent in order to recognize the great pressures on them to keep building up their arsenal. But Israel is already the largest recipient of American aid -- the yearly total approaches $3 billion.

Sen. Cranston asserts that the United States is morally bound to offset those arms it sells to Arabs formally at war with Israel. That this country has been careless in furnishing arms in the area is undeniable. But it has been even more careless in not relating arms sales to the contribution of Mideast nations to a full regional peace settlement. The danger to Israel does not arise simply from the fact that nearby countries are heavily armed. It arises from a political dispute -- the Israeli-Palestinian dispute -- for whose prolonging Israel bears its share of the responsibility.

In the past, Israel may have benefited in a narrow sense from the American practice of distributing arms across the Middle East with only secondary concern for the peace process. In conditions of abundant American sales to rich Arab states, however, Israel fears it may lose its advantage, unless there is an extraordinary new American financial commitment.

Secretary of State Haig took up the Arab-Israeli issue in his Mideast policy speech last night in Chicago. Regrettably, he did not address the arms question. More regrettably, he indicated that the administration is still not ready to give the Palestinian question the priority that American interests require.