Debate over American action in Central America is dominated by the spector of Vietnam. Some call for a bold stance to exorcise the American defeat there. Some feat that sending the first few advisers will start a certain descent toward a pit of hundreds of thousands of American soldiers locked in a fruitless and bloody jungle battle. Some predict the inevitability of revolutionary success against a corrupt and brutal government. iAnd some decry the analogy, saying El Salvador and Vietnam have little in common, so that the earlier experience does not augur the result in a new area.

The common measuring stick of these contending points of view is an image of Vietnam emanating from the Tet Attack of 1968 -- masses of guerrillas outwitting a corrupt local government and a ponderous and yet deadly American fighting force. With this image, the conclusion is inevitable that we should not repeat the experience.

But there were several "Vietnams." A blind application of only one in our decision-making process today only exacerbates the cost of Vietnam and its wounds upon the American body politic. Identification of these quite different "Vietnams" forces attention to real policy alternatives rather than obliterating the process by emotion and imagery.

John Paul Vann, a leading figure in our effort in Vietnam from 1960 to his death in 1972, once commented that Americans did not have 10 years' war experience in Vietnam (1960-1970) but rather one year repeated many times, due to the short tours most Americans spent there. But those with a longer perspective can clearly identify four distinct periods of the American wartime experience in Vietnam, each with its own characteristics.

The first period, 1960 to 1963, marked the start of Hanio's effort to overthrow the South, launched by a call by the Lao Dong Party for the overthrow of President Ngo Dinh Diem and his American allies. This was implemented by the reactivation of dormant Communist nets in South Vietnam and the infiltration of organizers and guerrilla leaders. After an initial period of indecision, the South Vietnamese developed the Strategic Hamlet strategy, to gather the smallest local communities for self-defense, with the military's role being to support these communities and act against regular forces. The American role was one of advice and support.

This program had its failings, but it seized the momentum of the "people's war" to the extent that Wilfred Bruchett, an Australian Communist apologist, later commented that "1962 belonged to the Government [of South Vietnam]." At this point, a combination of urban political oppositionists, Buddhist religious frenzy and Mandarin repression led to American encouragement of a junta of generals to revolt against President Diem. Diem might have won or might have lost the people's war on his own, but America's complicity in his overthrow produced instant turmoil and cemented America's responsibility for Vietnam's fate.

The second "Vietnam" is closest to the one commonly perceived, from 1964 to 1968. Most Americans served then as our involvement increased to 550,000 men. Instructed to find, fix and fight the enemy, they reacted with frustration and frequently fury before an enemy that only occasionally could even be found. The side effects of this massive military force in a tiny land dominate most fictinal and theatrical representations of Vietnam, making this period the basic reference point of Vietnam for most Americans. Its culmination was the Tet Attact of 1968, whose media drama so overshadowed its military failure as to win for the Vietnamese Communists a psychological victory.

The third "Vietnam" appeared between 1968 and 1972. The rural countryside was rebuilt and pacified by a revival of reliance upon village participation in defense and development. The combat was turned on the secret political enemy, not just his military forces. The contrast with the earlier period became ramatic in the opening of the Delta to land reform and commerce, the arming of local security and self-defense forces for village protection and the resettlement of millions of refugees in the villages from which they had been driven by the war. And most of America's military force was withdrawn from the country.

Vietnamese Communists are quite frank today in recognizing this period as the lowest point of their effort to defeat South Vietnam. The shift from the earlier period was best illustrated by the large North Vietnamese military attack in the spring of 1972, which took place only at three points along South Vietnam's borders (Quang Tri, Kontum and An Loc), with no countryside guerrilla assault. South Vietnamese, not American forces, fought back and stopped the attacks, helped by reinforcements from the Delta where they were not needed to defend against local forces and guerrillas. The American contribution was limited to advisers, extensive logistics support and B52 bombardment from the sky, with almost no combat force participation on the ground.

The fourth "Vietnam" appeared between 1973 and 1975. A "peace" treaty was pressed by the United States upon South Vietnam, which left North Vietnamese forces in place in South Vietnam and the border areas of Cambodia and Laos. American logistics support of South Vietnam's forces was cut back so that President Thieu's American-advised forward defense strategy became impractical. When in 1975 North Vietnam made a major assault at almost the same points as in 1972, American logistics were held back by Congress, and B52s did not fly. South Vietnamese tactical errors, not substantially different from some in 1972, led this time to total collapse before the oncoming North Vietnamese armor, artillery and regular forces. But even the North Vietnamese commander acknowledged that guerrillas played no part in his final victory. The boat people have dramatized the human dimension of the coucome; the degree to which it cast doubt on America's will and ability to stand by its allies is more ambigious.

The question then is: Which "Vietnam"? There is little doubt that no one wishes to see another Vietnam of the turmoil and blood from 1964 to 1968. Neither should we repeat the 1960 to 1963 period of America's turning against a friendly president and government for their imperfections and producing something worse. Nor, one hopes, do we want to see a Vietnam of 1973 to 1975, refusing aid to a nation battling a foe that makes no secret of its hostility to the United States. But the Vietnam of 1968 to 1972 offers a positive model of a leading role for political, economic and social programs to enlist a nation to develop and defend itself, with American advice and assistance in doing both