NIGHT AFTER NIGHT they slipped out of bed and sneaked into the computer room, sometimes working until daybreak. Nothing kept them away until counselors at the National Computer Camp locked the computer room doors nightly and unplugged the machines.

First thing in the morning they returned --a crowd of youths 10 to 18 years old with a fierce determination to learn at the $345-a-week camp in Simsbury, Connecticut. Last summer one computer whiz was so captivated that a counselor had to force him to go outside for a morning swim. Then he hurried back to the computer, taking time only for meals, until the lights went out at 10 p.m.

Something has caught hold of many fledgling summer campers, these children of a hurried generation accustomed to scheduled lives. In increasing numbers they are leaving home to "vacation" at specialized camps designed to help them become "professionals" before they have started their first job. They are minors with full-time summer majors, and their parents are willing to pay outrageous prices--$800 for two weeks is not uncommon--for the privilege of giving them this chance.

Although no one knows, for sure, how many single-interest camps have sprung up across the country during the last five years, competing with 9,000 to 10,000 traditional camps for the attention of youngsters, camping industry officials estimate there are hundreds. Most of the $2 billion-a-year camping industry is still devoted to instilling some 4 million youngsters with a generalist's grasp of the outdoors. Only time will tell whether the specialty camps are a lasting trend in the 200-year history of this nation's organized summer camps.

Among the most popular of the specialty camps are those devoted to football. Every summer countless 8- to 18-year-olds pull on their shoulder pads and jerseys to play contact football from coast to coast. At the Offense-Defense Football Camp in Fairfield, Connecticut, 700 boys wake up every day to calisthenics at 7:30 a.m. and spend the morning at "motivational" football talks and offense instruction, the afternoon in full pads for contact defense drills and the evening until 9 p.m. listening to "chalk talks" and watching football movies. Each boy spends $275 for a six-day session, highlighted by special clinics featuring such names as Miami Dolphins quarterback David Woodley and Denver Broncos place kicker Fred Steinfort.

Yet, director Mike Meshken hastens to say, "Our camp isn't a place to collect autographs. We don't use these glamorous stars' names and pictures in ads, unless they are under contract and then actually get out there and teach. It isn't a case of, 'Sit back and watch me.' "

According to Meshken, big-name football stars are sometimes only empty promises at sports camps. Parents should beware, he says, of flashy come-ons of stars who don't show or only make brief appearances to throw a few passes to a receiver while campers stand and watch.

Clearly, many youngsters are at football camps more because of pressure from the homefront than from the sideline coach. Meshken remembers a scrawny 10-year-old who once "sided up with the husky linemen on the field. The coach took one look at him and said he was built like a receiver. No, the kid says, my father told me I was a lineman because he was a lineman and captain of your team. He pointed to the coach's shirt with 'Yale' on it."

As surely as the image of camping has changed, the number of traditional camps has declined in the last decade, according to the American Camping Association, a non- profit organization which accredits summer camps. One out of every 10 traditional camps has folded in the last 10 years, forcing most camps to accommodate more than 100 campers to survive economically. The recession has already cut into enrollments at summer camps all over the country, but some specialty camps appear to be escaping the pinch.

"The specialty camps are probably attracting a higher income level than the generalist camps, but I think we are all feeling some of the effects of the poor economy," said Grier, president of the Virginia section of the American Camping Association. "We are hearing a lot more about how people are waiting for word on a furlough or a layoff. They say they just can't afford it this year."

If the depressed economy has slowed enrollments at some Washington area camps, others are thriving. Months ago the roster was filled for a four-week, $845 sports camp at Alexandria's Episcopal High School, a 130-acre boys boarding school. This summer 110 boys from 10 to 13 years old will spend a month learning not just one sport, but nine --softball, football, lacrosse, tennis, basketball, squash, swimming, track and soccer.

"If I encounter a parent who says he wants tennis, tennis, tennis, for his son morning, noon and night, I say the boy is not going to get it here," Nelson McDaniel, Episcopal High's sports camp director, said. "We have the same goals as a nature camp or a hiking camp in that we want to help the boys develop self-confidence and the ability to get along with others. Sportsmanship. We have never felt any pressure to push boys beyond their limits."

But what if a 9-year-old girl wants to become a tournament tennis player? Then she can pay $345 a week and enroll in a tennis camp at Yale University or the University of Virginia. The 4-Star Tennis Academy based in McLean sponsors tournament preparation programs for boys and girls 9-18 at both universities, plus Duke and St. Mary's College in Notre Dame, Indiana. "Only those players who are willing to exert maximum effort should consider signing up," says their brochure.

"Competition has become so fierce that if a youngster doesn't go to a sports camp, whether he is good or bad, another kid will pass him," said Hank Galotta, director of Sports America Basketball Camp in Laurel, Maryland. "But I definitely prefer a day camp situation like ours, as opposed to overnight. That type of thing is far too rigorous for kids 8 to 14. They just can't keep going 14 hours a day."

Yet in some camps the kids demand the right to be overworked or "enriched" around-the-clock and don't have the slightest interest in more ordinary summer camps. They want a structured, sometimes grueling, workout. Or they want to exercise their minds in college-level courses.

"Kids are more demanding," said Dr. Michael Zabinski, director of the National Computer Camp. "They want quality attention and they are very motivated. I mean, they stand out in line to get at the computers even when it is raining. Intellectually they don't want to become bored."

While others were hiking and climbing their way through summer camp last year, David Roe found himself in a Wellesley College classroom listening to an instructor ask, "Is there a god?" and "What will life be like in the next century?" Like thousands of other youngsters at universities across the country, Roe was attending a three-week academic enrichment camp asking himself questions that he had never thought about before.

"It turned a mediocre student into someone interested in learning for learning's sake," said his mother, Gail Roe of Potomac, Maryland. "Even though he loved the one summer when he learned to sail--that was fine when he was 11 or 12-- he was beyond the point where a typical summer camp situation was stimulating."

Looking back on last summer's experience, David Roe, now an 18-year-old high school senior, says, "I found that it was fun learning and getting exposed to people from all over the world. I never got that feeling in school."

But Hilary and Maggie Vaughan of Alexandria reacted differently after spending two weeks last summer at an "enrichment" camp for the gifted and talented at the University of Virginia. "It was too much like school," said Hilary, 13, who is going to a Colorado y outdoor camp this summer. Her sister Maggie, 14, has signed up for a sailing camp.

"Maybe kids just want to spend the summer playing, doing something where they don't have to think or put out or be 'enriched,' " said their mother, Patty Vaughan of Alexandria. "These academic enrichment camps are wonderful experiences, but it is nice to combine them with other camps. I would have been delighted if they wanted to go (to U.Va.) again, but they wanted something different."

This subject of general vs. specialized camps fires up Lloyd Ellings, director of a United Presbyterian summer church camp in Port Deposit, Maryland. Says Ellings, "Historically camp time was a time to relax and have a vacation in the outdoors. We are putting far too much pressure on our kids to be successful. If they are not high-achievers, they haven't made it. Some of these (overnight) camps have every second scheduled morning, afternoon and evening with little time to just relax."

Yet often these specialty camps give youngsters a heavy dose of a subject for the first time in their lives, exciting them into learning more. That happens regularly at the Hood Theatre Resident Camp, a $270, nine-day program sponsored by Montgomery County's Round House Theatre at Hood College in Fredrick.

"We live and breathe and do everything theater and it becomes a community. All 100 adolescents and 13 or 14 staff members are in it together," said Richard Averbuch, educational director of Round House Theatre. "We all share that fantasy, that dream to some degree or another. We entertain the kids and become kids ourselves, and the kids entertain us."

"Children are exposed to so many more extracurricular activities all year, and television has changed their outlook," says Linda Grier, director of Camp Friendship, a 460- acre outdoor camp in Virginia. "It takes a lot to excite and entertain children."

Or perhaps their idea of fun is changing.