Many factors shape foreign policy - interest, information, judgment, vision, prejudice, fatigue, fear, panic, stupidity - but there is one we tend to forget. That factor is ignorance - ignorance of the challenge, of the context, of how ignorant we may be.

Take the Persian Gulf crisis. Do we really know enough about the Mideast to act with confidence?The United States has not had serious historic experience in this region. A few missionaries went there in the 19th century, a few oilmen in the 20th and that is about it. We have no strong tradition of Arabist studies in our universities. Most of the time we don't know what we are doing in the Mideast.

Recall our policy toward Saddam Hussein: support when he committed "naked aggression" against Iran; unconcern when he gassed Iranians, massacred Kurds and murdered his own opposition; agricultural credits amounting to a billion dollars; opposition to economic sanctions against Iraq until the very eve of more of "naked aggression" against Kuwait.

One year Hussein is our pal; the next he is Hitler.

One year Hafez al-Assad of Syria is the king of terrorists; the next he is our pal: We will repent that too.

When we got so much wrong about the Mideast yesterday, the day before yesterday and the day before that, why do we suppose we have suddenly got it right today? Right enough to send thousands of Americans to their deaths?

Years after the Vietnam War, I asked a high official of the Johnson administration why they had ever supposed, as they said at the time, that North Vietnam was the spearhead of planned Chinese expansion into South Asia. Historians, I noted, could have told them the Chinese and Vietnamese had hated each other for a thousand years.

My friend replied: When it came to Soviet questions policymakers could turn to government experts such as Charles Bohlen, George Kennan and Llewellyn Thompson for informed counsel. In the case of China, John Foster Dulles had purged the State Department of the old China hands in the '50s. Our Far Eastern policy in the '60s thus plunged blindly ahead without benefit of expertise on China. So we got things wrong.

Alas, no Middle Eastern Bohlens and Kennans advise the government at high levels today. In consequence we are used, exploited and manipulated by wily locals in flowing robes who live in air-conditioned hotels and expect us to do their fighting for them.

If our ignorance of today's Middle East is considerable, our ignorance of the future there is total. Yet the case for war is increasingly based on the conviction that we have divine foreknowledge and know the shape of things to come.

Those who claim the gift of prophecy say unless we destroy Iraq's nuclear program, 5, 10 or 15 years from now Hussein, armed with the bomb, will terrorize the world. We have heard such prophecies before. It is the old - I thought discredited - argument for preventive war.

Some Americans were once so sure they could foretell the future that they called for preventive war against the Soviet Union and China. Does anyone regret that our government declined to drop the bomb?

Ignorance of the present, ignorance of the future: These are pardonable. No statesman, no nation, can expect to know everything. But ignorance of how ignorant we are is unpardonable.

(Arthur Schlesinger Jr. is professor in the humanities at the City University of New York.)