Lt. Harold L. McNeil has achieved the closest thing to immortality in a sultry East Texas town where dust turns swiftly to dust.

His memory endures beyond the usual limits of family grief, beyond the patriotic reflex to honor fallen soldiers. He died in Vietnam and so his family remembers more than just Lt. Harold L. McNeil, helicopter pilot, father, brother and son. They remember the futility of America's lost war.

For the McNeils and many other American families, the death of a loved one in Vietnam brought an added measure of grief and conflict.

It was nearly 21 years ago that an enemy bullet pierced McNeil's chest in Vietnam. The date was Aug. 12, 1964, only five days after Congress passed the Tonkin Gulf resolution, giving President Johnson authority to wage war in Southeast Asia.

Since that time the Army lieutenant's children have grown up, his father has died and the bronze plaque that identifies the Lt. Harold L. McNeil Armory here has lost its shine. All those years later, Ernest (Tex) McNeil Jr. still chokes up when he talks of the war that claimed his younger brother.

"It seems kind of futile to have gone through all that and still as far as I am concerned, I can't see what they accomplished over there," he said, gazing at a scrapbook of his brother's Army career. "In my own thinking, it seemed an awful waste to me. Not meaning the boys wasted their lives for nothing. They had a reason. Me, I cannot actually figure out the reason."

A compulsion to find a reason, to attach meaning and significance to the loss of a loved one, drives Vietnam war victims' families beyond the ordinary experience of bereavement, according to mental health professionals and veterans counselors who have worked with them.

"They are genuinely and humanly torn between on the one hand wishing to feel that the loss was for some purpose, that it mattered to be fighting in Vietnam," said Robert Jay Lifton, a psychiatrist who has written about Vietnam veterans and survivors of Hiroshima and the Holocaust. "Otherwise there seems to be the unendurable, unacceptable loss without meaning, without any sense of purpose . . . .

"I think it hurts more in Vietnam even than in other wars. I believe that the effort to give that death and loss convincing significance is harder, more difficult. That has to do with the whole country's feeling about the war -- not just the family." Timeless Feelings of Loss

The past recedes uncertainly for the families of men killed or listed as missing in Vietnam. For other Americans, great events fix the war's course in history -- from the Tonkin Gulf to the abdication of Lyndon Johnson, from the ascendance of Kissinger to the fall of Saigon. But the families remember Vietnam differently. Seemingly timeless, their feelings of loss eclipse historic dates and fleeting decades.

"Now I can talk about it," said Rosa Flott, a Rockville resident and widow of a Green Beret. "To me it's like a sad story, a sad book or a sad movie. Once in a while, you really think, 'Did I go through all this?' "

Dulled in the distance of time, their memories suddenly sharpen in the telling of the tale. And many Vietnam families seem to want to tell their tale, despite the anguish that vaults across the years.

Katherine and August Mannion's only son was killed in December 1966, and came home in a coffin on his 21st birthday. "I got up around 6:30," she said in her Baltimore row house home. "I happened to think, I didn't send this person a Christmas card. I was here at this table looking up addresses. It was 18 minutes after seven and the doorbell rang. I didn't see the Army car. I opened the door. I saw this officer. He kept saying to me, 'Are you Mrs. Mannion? Are you Mrs. August Mannion?' . . . . I went back to my kitchen and hollered, 'My son is dead, isn't he?' "

Parents struggle to justify losses suffered in a lost cause. Widows face remarriage, with one eye on the past. The children of lost servicemen discover their peers don't know or care much about Vietnam. All the while, sharp divisions, engendered years ago when the war was on, linger in the hearts and minds of the surviving families.

"There are a lot of commonalities among the feelings of surviving families and the feelings of the combat vets," said Heather Brandon, psychologist and author of "Casualties," an oral history of families who lost someone in Vietnam. "There is a tremendous amount of anger. There is a tremendous sense still 10 years, 15 years later, of loss. There is a lot of confusion about the war. I think you see in families a microcosm of the war."

For some families, there is consolation in the belief that the war was worth waging, or at least that the men who fought it would have won if the military had gone all out.

"My brother definitely believed in it so it had to be right," Tex McNeil said. "He said they could win that war in 30 days if they would just turn them loose. He said there wouldn't be a blade of grass left there." A Sense of Purpose

Medals mounted and hung on parlor walls, assertions that "he took 43 of them with him when he died" and religious faith that God shapes destiny -- these also are the building blocks of consolation. In the home of Robert and Louise Ransom in Williston, Vt., however, there is another kind of consolation, the kind that grows out of a conviction that the war was immoral.

Robert C. (Mike) Ransom Jr., the eldest of their six sons, was wounded by a mine while on night patrol near Quang Ngai and died eight days later. Until then Louise and Robert Ransom were just the anxious parents of another Army lieutenant. His death plunged them into the antiwar movement.

"For us it was a way of bringing something good out of what we lost," Louise Ransom said. "I think that when you are confronted with the death of a young person you try to get something of value out of it. I couldn't see anything of value for the country but I thought maybe if it would help to wake up people that it was worth putting myself on the line."

"When Mike was killed," her husband added, "the only thing that sustained us was our anger. I don't think we would have made it through without that. People would come and see us and say 'at least you have the satisfaction of knowing he died for his country' and we would throw them out of the house."

Just as Vietnam polarized the politics of the '60s and early '70s, so has it polarized the Vietnam families in the postwar period. The antiwar Ransoms disdain their son's medals -- "I believe they bought the silence of American parents with medals," Louise Ransom said -- while Katherine and August Mannion cherish theirs and disdain instead the memory of the antiwar movement.

On March 31, 1968, President Johnson announced that divisions over the war had persuaded him not to run for reelection. That same day, Wayne Hokenson, the adopted and only child of Edith and Carl Hokenson of Louisville, died in a mortar barrage. For Edith Hokenson, everything stopped on March 31, 1968.

"You have hopes for your children," she said, remembering the sudden loss. "You look forward to seeing them grow up and develop and seeing what is going to happen, what they are going to be. It's like stepping off the edge of the Earth because there is nothing there. I had visions of thousands and thousands of dollars of college tuition to be paid. And then all of a sudden I had nothing to save money for. Everything stopped."

The emptiness, for many Vietnam families, didn't start until after the initial shock wore off. It was numbness and a sense of unreality that first overcame Louise Kieffer, an Arlington woman married to an Air Force pilot. She remembered the day two Air Force officers broke the news of her husband's death to her and handed her a teletype describing it.

"I remember then a very strange feeling," she said. " . . . They sat down on the sofa and I sat down on a footstool that was across from a large coffee table. I started reading it and as I did I felt as though, well, I knew what it was saying and I knew that it was very bad and at the same time I felt as though I was up here on the bleachers of a stadium, somewhere from a height, looking down on all this happening. I guess it was a kind of escape mechanism." "I Knew It Was for Me"

Susan Tanfield of Burke, Va., had been shopping for a high chair for her infant daughter the day an Army chaplain came to tell her that her husband, John R. Hagood, was missing in action. The 24 hours that elapsed before he was confirmed dead, she said, were "very strange."

"I had not found the high chair the previous day and the next day I went back out. I felt like I had to do it. I'm not sure how well I was functioning. When I came home . . . there was an Army car parked there and I knew it was for me. I carried the high chair into the house knowing there was something in there I didn't want to hear. Bless my father. He was at the door. He hugged me very tight and I knew."

The grief that followed, in many cases, was extended and unresolved. Kieffer felt at times that grief was "the only thing I had."

"I remember one time being afraid, thinking, 'Oh, gee, what will I do when I am finished with this grief? Then I won't have this -- in a way it's really quite strange -- delightful misery.

"There were times I even enjoyed it. It just seemed to me the only thing I had," she said.

Not until Kieffer joined the local Gold Star Wives of America chapter did she leave some of her grief behind.

"You need to be with people who understand how you feel," she said. A Change in Directions

Many Vietnam families, reacting to their losses, found it necessary to make sharp changes in their lives and move in new directions.

Katherine Mannion became active in American Gold Star Mothers, volunteering her time in Baltimore's VA medical center.

The Ransoms became activists, first working against the war and then for amnesty for war resisters.

Edith Hokenson got a job with a travel agency and saw most of the world -- except Southeast Asia.

George and Helen Shine of Southbury, Ct., enrolled in the POW-MIA movement in the early 1970s and found themselves at odds with a government that never seemed to do enough for the 2,477 missing men.

"It's frustrating," said George Shine, a board member of the National League of Families of American Prisoners and Missing in South East Asia.

"We've been at it for so many years. We don't let the government alone . . . . Over the years, I think our government did very, very little. But the Reagan administration has given it great impetus."

Their youngest son, Jonathan, an Army platoon leader, was killed in a firefight. Their eldest son Anthony's Air Force jet disappeared over Laos without a trace. A third son, Alexander, was wounded in action and their daughter Sarah served in Vietnam with the Red Cross.

"With Jon," Helen Shine said, "I knew he was well and happy in heaven. But with Tony, you don't know. Was he wounded somewhere? Was he struggling to escape?" Defenders of War Effort

Despite their personal losses, the Shines are not embittered.

An officer in World War II and Korea, George Shine vigorously defends the war effort in Southeast Asia and Helen Shine likes to quote Theodore Roosevelt when she discusses her daughter and sons' military devotion.

"If you raised them to be eagles," she said, "you can't expect them to behave like sparrows."

For the widows of the war, a serviceman's death in Vietnam was especially disruptive. Efforts to remarry and establish a second family life, in many cases, failed in the face of old memories and laments for what might have been.

Susan Tanfield, who had been married for just two years when her husband was killed, remarried after the war, then divorced and later felt that perhaps the memory of her slain husband had interfered. "From the very beginning, I said to myself, 'You cannot compare, it's not fair.' I really don't think I did until after the divorce and then I would say, 'Well, this would not have been a problem, that wouldn't have been a problem.' " Unable to Find a Niche

Louise Kieffer had been married for 25 years when her husband was killed. "I couldn't find where I belonged after that," she said. "I had been married for so long. The military had been our life, as well as our bread and butter. I really couldn't find a niche. And really I haven't since then. I found as much as I am going to find."

The children of the Vietnam war dead, in turn, have had to cope with the fact that most of their age group have little interest in or understanding of the Southeast Asian conflict.

Monica Flott, the 14-year-old daughter of Rosa Flott, said her friends at school don't mention Vietnam. "They don't really care," she said. "All my close friends, they never talk about it. I don't really think they are interested in Vietnam . . . . If my father hadn't died in Vietnam, I don't think I would really care about it."

Amy Hagood, 16-year-old daughter of Susan Tanfield, said "nobody else I have ever met" had lost their father over there. Her friends have no way of understanding her experience. "My friends have often said that I'm so lucky that he died when I was only 6 months old, rather than after getting to know him," she said. "They are so wrong. I can't remember him at all. I have no recollection at all. I find myself wondering sometimes why am I crying about a person that I never even knew." Time Boils Down Issues

On Oct. 26, 1972, Henry Kissinger stood before a gathering of reporters at the White House to announce that "peace is at hand." For Keven Z. Goodno, half a world away, a different kind of peace had come. The Army helicopter crew chief was killed that day when his chopper was blown apart on a reconnaissance mission.

In Spring Grove, Minn., his parents are quietly living out their lives in a small town apartment. Vietnam added a dark stroke to the portrait of Alvin and Inga Goodno, a Norwegian American couple who were forced off the farm by Alvin Goodno's debilitating heart disease and driven into sorrow by the death of their son.

For the Goodno family and others as well, the passage of time has boiled down the war. Few families seem to have patience for the complexities of the conflict anymore. Citing "a gap as big as the Civil War," Louise Ransom said, "The division is between the people who say the trouble with the Vietnam War is that we didn't win it and those who say the trouble with the Vietnam War was that we should never have been there in the first place."

In the Goodno family the gap is between Alvin Goodno, who believes the war was "a waste of a lot of young men," and Inga Goodno, who clings to her dead son's enthusiasm for the fight. "I felt that if he felt that way about it, well, it was okay," she said.

If the war teaches different lessons to different people, so, too, does its legacy mix bitterness and pride. Even as the events of the war recede in time, the Vietnam families continue to search for a meaningful purpose in their loss. "What They Had to Do"

Edna McMahon of Woburn, Mass., believes today what she believed on April 29, 1975, when her son Charles was killed in a rocket and artillery attack at the Saigon airport. The very next day, the capital of South Vietnam fell to the northern invaders and the Americans were gone.

"We felt that if [fighting the war] was what this country had to do," she said, "that's what they had to do. I haven't changed my mind . . . . My youngest one joined when the other one got killed."

Robert Ransom sees it very differently. "That war heaped discredit on the United States and our son died perpetrating that folly," he said. "That's hard to take. It's very hard to take."

And Helen Shine finds solace in the words of her surviving son. "Alexander said to me, 'Mother, from the beginning of time, men have lost their lives in wars that they lost. It's just because there are two sides in every war. There are winners and losers.' "