A CURIOUS INCONSISTENCY marks the response of Israel and some of its American friends to the administration's decision to sell some $350 million in missiles and other munitions to Saudi Arabia.

The Israelis are never happy to see arms flowing to the hands of Arab states with which they are at war, but here they are prepared to countenance the sale. It is not just that the Israelis realize they have been treated with great generosity and understanding by the Reagan administration. They also realize that Washington has reason to make this gesture of American support for a friend in need. The Saudis are friends of the United States, and, threatened as they are by a rampant Iran, which has just bitten off yet one more piece of Iraqi territory and brought its forces near the border of a trembling Kuwait, they do need a timely and relevant showing of American constancy.

Rather amazingly, however, some of Israel's American friends are taking another view. These include the Israel lobby, the American Israel Public Affairs Committee and a number of members of Congress, including Sen. Alan Cranston (D-Calif.). The considerations that incline Jerusalem to go along with the sale do not impress them. Nor are they fazed to find themselves expressing more anxiety for Israeli security than the Israelis do. It seems to trouble them scarcely at all that the predictable result of blocking an American arms sale to a friendly Arab state is to have that state turn to another supplier, one that is glad to have the business and that makes no effort to impose the policy cautions that routinely accompany American arms.

What is going on in this particular instance has little to do with Israel's security. It has much to do with a test of wills. There is reason to wonder if those fighting the sale regard a contest with the administration over an ammunition package as something of a necessary warm-up for the campaign they intend to mount later this year to block delivery of the five early-warning AWACS aircraft that Congress agreed to sell in 1981 -- and that, incidentally, the Saudis have already paid $6 billion for.

Their success in either the small campaign or the large one would be a defeat for the national interest, which lies in helping friendly Arab states defend themselves against the real dangers in their region and in building thereby the sort of relationship with those states that works for, not against, Arab-Israeli peace.