( This is the first in a two-part feature, Part two. "The Effects of Herbicide Use in Vietnam," will appear tomorrow. )

There are military aspects of the war in Indochina which never appear on the weekly casualty lists. The use of herbicides in Vietnam by the U.S. military is one of these. In the years through 1969, approximately six million acres of forests and cropland were sprayed in Vietnam from the air. That comprises about one sixth of the total surface area of the country, and area the size of Massachusetts.

The use of herbicides has had an extreme effect on the people, the ecology, and the military conduct of the war. In order to obtain information about the consequences of herbicide use on the people and the land, the American Association for the Advancement of Science commissioned a group of scientists, the Herbicide Assessment Commission (HAC), to go to Vietnam and make such a study.

Matthew Meselson, Professor of Biology, was appointed by the AAAS to head the study in December 1969. By mid-summer, the commission had completed preliminary activities and begun an investigatory tour of South Vietnam.

With Meselson on the trip to Vietnam were Arthur H. Westing, a botany professor from Windham College, Dr. John Constable, Professor of Sugery at Harvard Medical School, and Robert Cook, a Yale graduate student. After conducting an investigation in Vietnam during August and September, the Commission returned to this country and began to sort out their data and observations. A preliminary report on their work was issued in December at the AAAS 1970 meeting, but much of their laboratory work remains to be done.

THE STORY of herbicide use in Vietnam is still incomplete-crop destruction by chemical spraying is still being used as a war tactic by the U.S. this year. However, the U.S. government has announced that no new chemicals are presently being bought, so that only existing stocks are being used; presumably, herbicide use will finally end soon. But the military use of herbicides in Vietnam is not new, and its lasting effects will be felt long after a change in American war policy.

Herbicides were first used experimentally in 1961 and have been used every year since then. From a relatively small amount of land sprayed in 1962, 5681 acres, herbicide use peaked in 1967 at 1,707,758 acres and was down to 1,287,115 acres in 1969, the last year for which data are presently available. (For comparative purposes, think of the state of Massachusetts as 6 million acres.)

HERBICIDES are chemicals which are designed to kill or reduce vegetation. If they cause the leaves to fall but do not kill the entire plant, they may be called defoliants. Although the U.S. Chemical Corps in Vietnam sometimes calls its spraying "defoliation," the chemicals used have proved to be herbicides.

Three chemical herbicides have been used in Vietnam in large quantities. They are called Orange, White, and Blue, names derived from the color of paint identifying the drums during shipping from the United States to Vietnam. Orange and White are primarily used to clear forest land, while Blue is used for crop destruction. Orange has been the most extensively used, accounting for about sixty per cent of the herbicide-treated land. Its usage was stopped by the Department of Defense in April 1970 after laboratory tests showed one of its ingredients, 2,4,5-T, to cause gross physical defects in animals.

White was brought to Vietnam in 1966, when U.S. production capacities for 2,4,5-T were too slow to satisfy the demand for Orange. White is also mainly used for forest clearing, but seems to have longer-lasting results than Orange.

Blue is used for crop destruction primarily, acting very effectively against grasses and rice. Blue contains derivatives of arsenic compounds, and the HAC is now working out laboratory tests which should be able to detect traces of these compounds in human hair; that way, the interaction of the herbicides with the human food chain should be clarified, and some of the long-lasting effects of the herbicides may become known.

The military sprays herbicides in Vietnam from planes, helicopters, and some ground equipment. Most of the spraying, though, is done from C-123 cargo planes. In the seven years preceding 1961 more than 11,000 spray flights were made by these planes; each flight effectively kills vegetation in an area approximately 85 meters wide and 15 kilometers (81/2 miles) long.

The spraying during the last decade has been directed towards four different kinds of targets: mangrove forests, hardwood forests, strip spraying (along roads and canals) and crops.

Mangrove forests cover about 3,000 square kilometers of South Vietnam, along the coast of the Delta in the South and to the southwest of Saigon. About half, 1,400 square kilometers, has been sprayed with herbicides, as estimated by the HAC. The HAC preliminary report discusses some of its findings:

"For as yet undetermined reasons, mangrove species have proved to be particularly sensitive. Essentially all vegetation is killed. Preliminary aerial and ground inspection by the Commission showed little or no recolonization by mangrove tree species after three or more years. . . . Without vegetation, the area obviously cannot support most of the bird and ground animal species associated with the previously existing mangrove forests. A possibly important exception are crabs, large numbers of which were observed in barren areas. By devouring seedlings, crabs may be retarding revegetation. There are signs of erosion along the denuded coastlines but as yet they are slight. Major typhoons, which on the average strike the mangroves about every five years, have not occurred since herbicide was sprayed."