Something important is escaping us in the Persian Gulf crisis. It is the fact that U.S. involvement in previous wars, even when precipitated by executive action, has always come in response to attack on the United States or one of its allies.

In other words, we only fight to defend ourselves.Virtually every American president has realized an important truth - that no military action can be successful unless the American people are behind it. As he approached the Civil War, Abraham Lincoln realized that before the North could take action, the South would have to "fire the first shot."

The firing on Fort Sumter started the war, even though some historians have accused Lincoln of "maneuvering the South into firing the first shot."

Psychologically, the important thing was that the Union could sincerely react to attack and interpret the war as defensive action.

In World War I, Woodrow Wilson, the avowed pacifist, was determined to promote peace even when German submarines torpedoed the Lusitania, a British ship carrying 128 Americans. He even ran for re-election in 1916 on the campaign slogan, "He kept us out of war."

It was only after the Germans unleashed "unrestricted submarine warfare," in 1917, thinking they could win in Europe before the Americans could make a difference, that Wilson finally relented.

During Franklin Roosevelt's administration the decision for U.S. entry into the war came after the Japanese attack on Pearl Harbor on Dec. 7, 1941. Roosevelt, like Lincoln before him, was convinced that if a war occurred, Japan would have to make the first move.

Even though the attack was more ghastly than Roosevelt envisioned, he could confidently announce to the country afterward that "Dec. 7th is a day that will live in infamy" - and get overwhelming support from a country that understood the principle of self defense.

The Korean and Vietnam wars were fuzzier enterprises - limited wars in the middle of the Cold War. Korea was a "police action" without congressional support to aid the South Koreans against the North. When the North Koreans invaded South Korea, crossing the sacred 38th parallel in June 1950, Harry Truman took it as an attack on an American ally.

The Korean War became so unpopular that it politically destroyed Truman.

Vietnam grew steadily through several presidents, who continued to increase the number of military advisers to South Vietnam. Lyndon B. Johnson took military action with the help of the Gulf of Tonkin Resolution passed by Congress in reaction to a perceived attack by North Vietnamese gunboats on American destroyers in the gulf.

That happened in 1964. By 1968, the American force in Vietnam exceeded 538,000 troops. At first American support was strong, as it had been in Korea, but it deteriorated so badly that it destroyed Johnson's presidency.

All of this seems germane as American strength in the Persian Gulf has quickly grown to 400,000 troops without benefit of either attack on the United States or congressional action. If we think the Korean and Vietnam wars were hard to justify, try explaining to your kids why there are 400,000 troops in the Persian Gulf.

This is the first time the United States has taken such significant military action without any pretense of self- defense.

An attack by Iraq upon Kuwait does not constitute an attack upon the United States or upon an allied state where the president is obligated or authorized by Congress to respond in self defense.

That does not mean that the Iraqi attack on Kuwait was acceptable, but U.S. action there is historically unjustifiable. Moreover, if our motive is to stop aggression anywhere, there have been many other countries in the last 20 years who deserved U.S. help just as much as Kuwait. If U.S. action there is not self defense - what is its justification? Oil?

Considering the fact that Truman's presidency was ruined by Korea and Johnson's by Vietnam - even when an attack on the United States or an ally was the issue - George Bush should take a new hard look at the Persian Gulf before it is too late.