THE WAR between Iran and Iraq has produced -- or, more precisely, confirmed -- a quiet but momentous shift in American foreign policy. It has come about in respect to Saudi Arabia and the other oil producers in the Persian Gulf. The United States now accepts a commitment to defend them not only against the depredations of an "outside force," as President Carter stated in the "Carter Doctrine." As this crisis shows, it also accept a commitment to defend them against threats mounted from within the region. In either case, a "vital interest," the oil, is at stake. This is the basis on which the administration has dispatched American equipment and military men to aid in the air defense of Saudi Arabia and positioned other American forces to protect those units. Having long implied a general intent to protect its Gulf friends, the United States is now -- by putting military forces, including combat forces, into a potential combat zone -- showing itself ready to go to war for oil.

Saudi Arabia, for all its billions, cannot yet muster a defense that it trusts. It is reluctant to advertise either its military insufficiency or its reliance on Israel's patron by making much of its need for an American umbrella. Nor do the Saudis -- or for that matter the Americans -- wish the providing of the air-warning system to be seen as payment for the marvelously helpful Saudi decision to increase oil production to cover the oil removed from the market by the war.

The Saudis, or some in the ruling family, do see the absolute and symbolic value of American crisis protection, however. And they hope to inherit the ground radar that the Americans are bringing in for the duration. It was the implicit half of the range-extending system for the F15 warplanes whose explicit half, including fuel pods, bomb racks and Sidewinder missiles, has been stalled by Israeli protests for months.

Secretary of Defense Brown, who is not unaware that this is an election year, says the risk of attack on Saudi Arabia is reduced by making the American commitment clear. The signs are that the legislators whom the administration has consulted -- informally, since the consensus is that the War Powers Act is not yet engaged -- accept this argument. Certainly the dependence of the United States and its allies on Gulf oil makes a powerful case.

Yet why has the administration not specified the particular threat which it is responding? Is not intra-regional upheaval so endemic as to foreshadow repeated American interventions to safeguard the oil? How can the United States' European allies be so summarily frozen out of the action -- by, no less, the secretary of defense, who consigned them to "their" regions (which?) on television Sunday?What about the side-door provision of radars in a crisis -- without congressional screening? What are the overall implications, military and political, of putting the United States in the way of hostilities in the Gulf? These are just some of the questions that need close attention now.