In college dormitories and high school history classes across the country, the thoughts of young Americans suddently shifted yesterday from exams and jobs to the prospect of flighting in faraway lands.

The reactions of 18- to 26-year-olds to President Carter's call for resumed draft registration were as varied as they were plentiful, ranging in tenor from unstinting support to the "Hell no, we won't go" protest of the Vietnam era.

"I was in bed last night listening to Carter, and the first thing I thought was 'Oh, no,'" said 19-year-old Henry Carter of the District of Columbia. "I began to think of all my plans for the future, and it was like they were going down the drain."

But only five miles away, at Montgomery Blair High School in Silver Spring, 17-year-old senior David MacArthur was thinking something quite different. "If you have a right to live in this country," said MacArthur, "then you have a responsibility to fight for it."

While the discussions that blossomed virtually everywhere young people gathered yesterday harkened back to Vietnam, the mood seemed less hostile than it was a decade ago.

"You won't see any riots this time," said Bethesda-Chevy Chase junior Phil Scott. "There's a big split in student opinion.

Indeed for some, the resumption of draft registration had a lighter side, with students "brushing up on their Canadian" or looking for women to marry as a way to get exempted."All my friends said they've gonna get women and get married," laughed Blair High senior William Sublet.

For others, however, the world situation was no laughing matter and the beat of patriotic drums was strong.

Chris Miller, 23, a military veteran and a freshman at Old Dominion University, declared: "America is just a second-rate power now, but we are strong enough to do something about it. We have to stop Russian aggression." s

At Langley High School in McLean, Cliff Hendrix, a student, said, "No one who is sane can say war is nice, but if war has to be fought, then people from all walks of life should be involved.

"A lot of people," he added, "might be resentful because of the Vietnam war, but if they realized Russia is behind a lot of the problems in the world they would realize it's their patriotic duty."

For the most part, it seemed, the prospect of draft registration was met with uncertainty and confusion. Thousands of potential draftees called the national headquarters of the Selective Service System yesterday, seeking information.

At the big brick office building at 600 E. St. NW, the main receptionist lost her voice, television crews roamed the floors, and Selective Service System workers -- whose ranks have dropped from 9,600 at six regional offices during the Vietnam war to about 100 -- tried to reassure anxious callers.

"No one's being registered at this time," repeated records officer Betty Alexander to one caller after another. "We're not issuing draft cards."

The plan to resume draft registration, which Congress will consider next month, forced many young people to reconsider their casually held views on America's role in the world, and rekindled old debates such as the role of women in combat.

"I'm a women's libber but I don't think women can handle combat," said 19-year-old Susan Sherman of Staten Island, N.Y.

At the School Without Walls in Washington, differences of opinion on the role of women led to roughhousing out on the campus lawn, with two ardent supporters of women in combat ganging up on 19-year-old John Hargadon.

"Women shouldn't be in combat," said Hargdon. "No matter how much you train a woman in hand-to-hand combat, a man will come out on top. Except for the Chinese. They got tough women."

"If we don't go and fight we'd blow it all," said 17-year-old Ruth Gutekunst, putting a headlock on Hargadon. "It would totally demolish ERA."

More intellectual exchanges marked much of the debate at colleges around the country, with patriotism, self-sacrifice, and conscience among the issues discussed.

At the University of Michigan in Ann Arbor, junior Dan Solomon dusted off an old "No Draft, No Way" button and pinned it to his lapel, but indecision and uncertainty belied the demonstrative gesture. "To tell you the truth, I'm scared as hell," he said, "I won't be drafted. I'll refuse. But I'll have to decide whether it's hypocritical to register and then not go."

But for every would-be draftee ploting a route to Canade or Mexico, there were college students who stood squarely behind the resumption of the draft. Rich Mitchell, 20, a sophomore at Roanoke (Va.) Western Community College, said, "I think we need the draft now. Ever since we withdrew from Vietnam, the country's confidence has shrunk. We shouldn't go into a war ready to compromise."

The wide range of reactions among college students was paralleled in Washington area high schools. But at schools such as Montgomery Blair in Montgomery County and Ballou in the District, some black students said they had no desire to get involved in what they called a "white man's war."

At Ballou, students in Ronald Floyd's fourth period sociology class talked about the draft all morning, but many, the teacher said, did not understand this country's interplay with other nations. "They live in a separate society," Floyd said. "Although they are aware of things going on in the rest of the world they don't see any direct linkup."

To many of these teen-agers, the draft and the distant machinations of the Soviet Union and Iran were considered unfair interruptions in their lives.

"This is unfair to young people," said Ballou senior Norval Williams. "We're just starting our lives. Our parents tell us they want things to be better for us than they had. And then this draft thing comes. The war would kill our dreams before they ever started."

Some students with no special plans or ambitions said they welcomed the idea of the draft, not for any patriotic principles but for taking the decision with what to do with their lives out of their hands. "A lot of my friends want the easy way out," said 17-year-old Blair senior Richard Pineda. "Seniors have to find a job, make up their minds what to do. The draft takes that off their hands."

With graphic films such as "Apocalypse Now" and "The Deer Hunter" fresh in their minds, some high school students who might have been tempted by the "romance of war" said they had been jolted by its more brutal realities.

"I saw 'Apocalypse Now' and I couldn't believe war was like that," said Henry Carter.

"I saw the movie and decided it's not for me," said 15-year-old Alan During, a sophomore at Bethesda-Chevy Chase. How was During planning to avoid the draft if his time came? "John the Army band," he said, heading for his trombone class.

Already, faced with no more than the threat of registration, some potential draftees are exploring ways to become conscientious objectors.

"If I've answered one call from a CO I've answered a million." Selective Service employe Betty Alexander said.

Her switchboard did light up with several calls from young men wanting to enlist immediately, such as 17-year-old Tom Clifford, who cried out, "I say we take some hostages, I say we go now."