Americans, perhaps as many as 100 million teens and adults, don't get enough sleep - not because they can't sleep but because they are too busy working and playing.

The result, according to an article in the current issue of Esquire, is a lack of alertness that can be dangerous, particularly when compounded by alcohol.The sleep-deprived may suffer lapses of attention and information processing ability while they are driving, caring for children or otherwise affecting someone else's welfare.

Dr. Thomas Roth, who heads the Sleep Disorders and Medicine Division at Detroit's Henry Ford Hospital, said it is not the level of sleep loss that worries him.

"It's the ignorance of the consequences," he said. "People know eating a lot of fats makes them vulnerable to heart disease. But they think the less they sleep, the better they are.

"You have to recognize that if you're studying for exams or making deadlines and quotas, and then you have a drink to celebrate, you're in double trouble. A trivial second drink after meeting a deadline is really dangerous."

Roth's experiments include feeding vodka and tonic at 9 a.m. to volunteers who are sleepy, rested, drunk and sober.

Test results show that sleep loss and alcohol produce similar sedative effects - both make you sleep - but they also interact. Each heightens the effect of the other.

"For a hard worker sleeping five hours a night, one beer might have the same effect as three or four Scotches for someone who sleeps nine hours a night," Roth said.

Age is another factor in sleep problems, according to psychologist Richard Coleman, a specialist in chronobiology and former codirector of the Stanford University Sleep Disorders Clinic who now heads a consulting firm.

"People naturally develop more sleep disorders as they get older," Coleman said, "just as they get more heart disease and so forth. Two reasons interlock, as usual: environment and physiology; nurture and nature."

Environment involves people sacrificing sleep time in favor of work and play. Many rate themselves alert when they are not. The Multiple Sleep Latency Test, which indicates how prone you are to napping, is one way to test how sleepy or alert you are.

"Ten- to 12-year-olds score the best," Coleman said. "They're very alert and zestful. One reason is that normally they have one long, regular sleep period every day, seven days a week."

By college age, people test much sleepier during the day.

Physiology determines that as we reach our 20s, 30s and beyond, we have decreasing amounts of Stage 4 or deep sleep, which seems to have restorative value. It occupies about a quarter of a child's sleep time but only an eighth or less of an adult's.

Mary Carskadon, a professor at E.P. Bradley Hospital at Brown University and a member of the National Commission on Sleep Disorders Research, agreed, saying:

"The ability to consolidate sleep - to have a long period of sleep without arousal - seems to lessen with age. Arousal means coming up from sleep, a change in brain waves that means technically you're no longer asleep. It may be so short you don't realize you're awake - four or five seconds. As people age, we see more and more of what you might call microarousals."

She added that as we age we also sleep worse. Between the ages of 10 and 20 we lose 40 to 50 percent of the Stage 4 sleep we had at 10.

"The rate of decline lessens after age 20," she said, "but the process continues through the rest of life."