At McKinley High School in Washington, a senior who is asked about the war in Vietnam responds in earnest, "Is that the one where they dropped the bomb on Hiroshima?"

That is an extreme example, but visits to four high schools in the Washington metropolitan area, talks with teachers and students and a look at the history textbooks in high schools, show that the Vietnam war as a lesson has faded, almost become lost.

A history text used at Groveton High School in Fairfax County had a separate six-page section on Vietnam in its 1969 edition. The 1975 edition of the same book treats Vietnam in a 2 1/2-page section titled, "Vietnam; The Black Revolt; The Student Protest."

Looking at textbooks used in local high schools, a reader who lived through the Vietnam era is struck and surprised by what is not there. Absent in several books is even passing mention of the Kent State shooting, the May Day demonstration, the My Lai massacre, the 1968 Chicago Democratic convention or even North Vietnamese leader Ho Chi Minh.

Also missing from the books are the photographs that burned themselves into the memory of those who lived through the times - the naked and frightened Vietnamese girl fleeing down the road away from a napalm attack, the suspected Vietcong terrorist having his brains blown out, Buddhist monks burning themselves or American helicopters evacuating troops with soldiers hanging from the skids.

For many students in the area's high schools, Vietnam will be reduced to a couple of paragraphs from these texts. Or it may be a teacher's brief recital of a confusing array of facts in the rapid-fire final weeks of the semester when time catches up with history and students are more apt to be concentrating on the coming summer. Several teachers say they may not even get to the Vietnam era.

There are students who will learn more about the war, but they are the exception. In courses in contemporary issues for sophomores at Walt Whitman High School in Bethesda, for instance, teachers may spend a few days on the war that divided the nation.

In such a class one day last week the words "secret bombing . . . McGovern . . . Vietnamization" bounced off the walls of the sunny classroom like echoes from the past and seemed out of place.

Outside the classroom, students were hanging posters advertising the senior prom and majorette tryouts.

Ashby Bryson, a teacher at Whitman, said he once led his class in antiwar cheers to try to recreate the times and the passion they provoked. "Ho-Ho-Ho Chi Minh; NLF is gonna win," and "Hey hey, LBJ; how many kids did you kill today," they chanted.

But for his students the emotion just was not there.

Nonetheless the students look back on the war with a youthful certainty.

"It was stupid," said Pat Prevo, a junior at Bowie High School in Prince George's County. "We didn't have any reason to go in and we never got anything out of it."

Vietnam comes through to most students in terms that are stark and absolute - that it was all wrong, that it made no sense, that it was a grotesque failure totally at odds with American national purpose.

The students at the four schools used words like stupid, dumb, disaster and mistake to describe the war. They are bemused by what they consider an almost quaint fear of communism that propelled American into Vietnam. They are at a loss to understand how it happened.

"I think the biggest mistake was killing all those innocent people," said Frances A. Pullian, a junior at McKinley. "I don't even know what the war was about."

"With all the movies that have come out this year, 'The Deer Hunter,' ' Friendly Fire,' and all that, they give the impression that our government was wrong," said Larry Greenberg, a student at Whitman. "For those who weren't there, those in our generation, certainly everybody is going to say the government was wrong."

"I feel like we're missing something," he said later. "There's something in the fact that the whole government was for it. We must be missing something if we can only see why we should have been against it."

While the students appear to perceive American motives of North Vietnam and others who fought against South Vietnam.

"Why weren't there protests in North Vietnam?" asked Joseph Wrona, a Whitman teacher, of his class. Wrona was asking generally whether there might have been oppression and suppression of dissent in North Vietnam as well as in South Vietnam.

"Because they were all happy and healthy," said one voice from the class. "Because they were all fighting for the same thing," came a chorus of several others.

The war has bred a generation of isolationists among current high school students, most teachers say. "They don't want us to get involved, and that applies not just militarily but to economic assistance as well," said Stanley Boyd, a teacher at McKinley.

"We should worry more about the problems in the United States than going off to those foreign states," said Sonja Ahmad at McKinley.

"They're learning the lesson of the previous war," said teacher Elizabeth Mark at Groveton High School. Just as feelings that the United States should have intervened sooner in World War II prompted some American actions in the post-World War II period, a feeling that the United States should never have gotten into Vietnam has provoked feelings of isolationism, she said.

But she added: "It may be the wrong lesson."

Whatever the lesson, it is not one that interests high school students particularly.

"The one thing I remember about the war was looking at the TV and seeing a bunch of dead bodies," said Whitman student Henry Strauch, who said the pictures didn't impress him much.

Many students were still in elementrary school when American troops were withdrawn from Vietnam. Their impressions of the war are second hand.

"Ti feels kind of strange, like we're on the outside looking in," said Arjun Chammugam, another Whitman student.

"Students don't get excited about it," said Mark. "It's amazing to me. It's so quick. It's over," she said.

In contrast to the students, the teachers' memories of the war are sharp and often painful. For some, it revives memories of long, cold nights on anti-war marches or combat experience in Vietnam. Only a few teachers said they had not been active on either side of the debate over the war.

Teachers often supplement the texts with other material of their own experience. At Bowie, Mary Lou Mortlock said she invites a former student who served in the war to show slides and talk about his experiences.

Another Bowie teacher, Thomas Boltz, who served as an Army lieutenant in Vietnam and teaches at Bowie, uses photographs he took while he was over there.

"I have a feeling of bitterness," said Boltz. "The thing that makes me so bitter is what I feel is the stigma and unfairness given to the men who went over there." Boltz said he tried to attack myths that have grown up around the war, such as the myth "that everybody in combat was a cold-blooded killer" or "that everybody ran off to Canada."

With all the immediate and historical perspective the teachers say they try to bring to the subject, students are still less interested in Vietnam than World War II or more immediate foreign crises that could curtail gasoline supplies.

"By and large the war's ignored, neglected, not treated," said Boyd, at McKinley. "That's unfortunate because the students are not learning anything from the war." Boyd is a Quaker who went to North Vietnam as part of a four-member teacher delegation sponsored by the American Friends Service Committee in 1975 and was there during "the liberation of South Vietnam."

"Anything that happened 5 years ago could have happened 100 years ago" in terms of student interest, said Jack Hiller, chairman of the social studies department at Groveton High School.

"Perhaps the attitude of our students is like the attitude of German students to World War II," said Hiller, who said he supported the war and still believes the U.S. record in the war is better than generally perceived. "They don't want to think about it."

Later, walking down a hall, Hiller said, "I don't know if the kids feel that. Maybe we feel that and don't tell them about the war.

"Americans don't like losers," he said.